Difference between revisions of "Aging" - New World Encyclopedia

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[[File:Old woman with young baby boy.JPG|thumb|right|300px|95-year-old woman holding a five-month-old boy]]
 
[[File:Old woman with young baby boy.JPG|thumb|right|300px|95-year-old woman holding a five-month-old boy]]
  
'''Aging''' or '''ageing''' is the process of becoming older. The term refers especially to [[human]]s, many other animals, and [[fungi]]. In the broader sense, aging can refer to single cells within an organism which have ceased dividing ([[cellular senescence]]) or to the population of a species ([[population aging]]).
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'''Aging''' or '''ageing''' is the process of becoming older. The term refers especially to [[human]]s, many other [[animal]]s, and [[fungi]]. In the broader sense, aging can refer to single cells within an [[organism]] which have ceased dividing ([[cellular senescence]]) or to the population of a species ([[population aging]]).
 
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In humans, aging represents the accumulation of changes in a human being over time and can encompass [[Human body|physical]], [[psychological]], and social changes. Reaction time, for example, may slow with age, while memories and general knowledge typically increase.  
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This article focuses primarily on humans. Aging represents the accumulation of changes in a [[human being]] over time and can encompass [[Human body|physical]], [[psychological]], and social changes. Reaction time, for example, may slow with age, while memories and general knowledge typically increase. Society's view of aging, for example valuing youth over experience, affects a person's self-perception of their own aging. A belief in an [[afterlife]], the continued existence of an eternal [[spirit]] or [[soul]] after the [[death]] of the physical body, gives a different view to aging and reduces the stress associated with physical deterioration.
 
 
  
 
== Definitions ==
 
== Definitions ==
Mortality can be used to define biological aging, which refers to an organism's increased rate of death as it progresses throughout its lifecycle and increases its chronological age.<ref name=McDonald>Roger B. McDonald, ''Biology of Aging'' (Garland Science, 2019, ISBN 0815345674).</ref> Another possible way to define aging is through functional definitions, of which there are two main types: The first describes how varying types of deteriorative changes that accumulate in the life of a post-maturation organism can leave it vulnerable, leading to a decreased ability of the organism to survive. The second is a senescence-based definition which describes age-related changes in an organism that increase its mortality rate over time by negatively affecting its vitality and functional performance.<ref name=McDonald/>  
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Biological aging refers to an [[organism]]'s increased rate of death as it progresses through its lifecycle and increases its chronological age.<ref name=McDonald>Roger B. McDonald, ''Biology of Aging'' (Garland Science, 2019, ISBN 0815345674).</ref> Another possible way to define aging is through functional definitions, of which there are two main types: The first describes how varying types of deteriorative changes that accumulate in the life of a post-maturation organism can leave it vulnerable, leading to a decreased ability of the organism to survive: "Aging is the progressive accumulation of changes with time that are associated with or responsible for the ever-increasing susceptibility to disease and death which accompanies advancing age."<ref>D. Harman, [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC349208/ The aging process] ''Proc Natl Acad Sci U S A'' 78(11) (November 1981): 7124–7128. Retrieved May 31, 2022.</ref> The second is a senescence-based definition which describes age-related changes in an organism that increase its mortality rate over time by negatively affecting its vitality and functional performance.<ref name=McDonald/>  
 
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{{readout||right|250px|Aging is the natural biological process that all [[animal]] life, including [[human being]]s, go through from conception to [[death]]}}
An important distinction to make is that biological aging is not the same thing as the accumulation of [[disease]]s related to old age; ''disease'' is a blanket term used to describe a process within an organism that causes a decrease in its functional ability.<ref name=McDonald/> Aging is the natural and inevitable biological process that all [[animal]] life, including [[human being]]s go through from conception through birth to [[death]]. While death by other external causes, such as disease, accident, predation, and so forth, is common, it would occur naturally due to aging if such causes were absent.
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An important distinction to make is that biological aging is not the same as the accumulation of [[disease]]s related to old age; ''disease'' is a blanket term used to describe a process within an organism that causes a decrease in its functional ability.<ref name=McDonald/> Aging is the natural and inevitable biological process that all [[animal]] life, including [[human being]]s, go through from conception through birth to [[death]]. While death by other external causes, such as disease, accident, predation, and so forth, is common, nonetheless death would occur naturally due to aging even in the absence of such causes.
  
 
== Biological basis ==
 
== Biological basis ==
The causes of aging are uncertain;<ref>{{Cite journal|last=Liochev|first=Stefan I.|date=2015-12-17|title=Which Is the Most Significant Cause of Aging?|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4712935/|journal=Antioxidants|volume=4|issue=4|pages=793–810|doi=10.3390/antiox4040793|issn=2076-3921|pmc=4712935|pmid=26783959}}</ref> current theories are assigned to the damage concept, whereby the accumulation of damage (such as [[DNA oxidation]]) may cause biological systems to fail, or to the programmed aging concept, whereby problems with the internal processes (epigenomic maintenance such as [[DNA methylation]]<ref>{{Cite journal|last1=Ghosh|first1=Shampa|last2=Sinha|first2=Jitendra Kumar|last3=Raghunath|first3=Manchala|date=2016|title=Epigenomic maintenance through dietary intervention can facilitate DNA repair process to slow down the progress of premature aging|url=https://iubmb.onlinelibrary.wiley.com/doi/abs/10.1002/iub.1532|journal=IUBMB Life|language=en|volume=68|issue=9|pages=717–721|doi=10.1002/iub.1532|pmid=27364681|issn=1521-6551|doi-access=free}}</ref>) may cause aging. Programmed aging should not be confused with programmed cell death ([[apoptosis]]). Additionally, there can be other reasons, which can speed up the rate of aging in organisms including human beings like obesity<ref>{{Cite journal|last1=Ghosh|first1=Shampa|last2=Sinha|first2=Jitendra Kumar|last3=Raghunath|first3=Manchala|date=May 2019|title='Obesageing': Linking obesity & ageing|journal=The Indian Journal of Medical Research|volume=149|issue=5|pages=610–615|doi=10.4103/ijmr.IJMR_2120_18|issn=0971-5916|pmc=6702696|pmid=31417028}}</ref><ref>{{Cite journal|last1=Salvestrini|first1=Valentina|last2=Sell|first2=Christian|last3=Lorenzini|first3=Antonello|date=2019-05-03|title=Obesity May Accelerate the Aging Process|journal=Frontiers in Endocrinology|volume=10|page=266|doi=10.3389/fendo.2019.00266|issn=1664-2392|pmc=6509231|pmid=31130916}}</ref> and compromised [[immune system]].
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The causes of aging are uncertain, but appear to involve a number of factors.<ref>Stefan I. Liochev, [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4712935/ Which Is the Most Significant Cause of Aging?] ''Antioxidants (Basel)'' 4(4) (December 2015): 793–810. Retrieved May 31, 2022.</ref> The factors proposed to influence biological aging fall into two main categories: ''programmed'' and ''damage-related''. They are not necessarily mutually exclusive.  
  
Researchers are only just beginning to understand the biological basis of aging even in relatively simple and short-lived organisms, such as [[yeast]].<ref name="Janssens 2015">{{cite journal | vauthors = Janssens GE, Meinema AC, González J, Wolters JC, Schmidt A, Guryev V, Bischoff R, Wit EC, Veenhoff LM, Heinemann M | display-authors = 6 | title = Protein biogenesis machinery is a driver of replicative aging in yeast | journal = eLife | volume = 4 | pages = e08527 | date = December 2015 | pmid = 26422514 | pmc = 4718733 | doi = 10.7554/eLife.08527 }}</ref> Less still is known of mammalian aging, in part due to the much longer lives of even small mammals such as the mouse (around 3 years). A [[model organism]] for studying of aging is the [[nematode]] ''[[Caenorhabditis elegans|C. elegans]]''. Thanks to its short lifespan of 2–3 weeks, our ability to easily perform genetic manipulations or to suppress gene activity with [[RNA interference]], or other factors.<ref name="RothmanSingson2012">{{cite book| vauthors = Wilkinson DS, Taylor RC, Dillin A | veditors = Rothman JH, Singson A | title = Caenorhabditis Elegans: Cell Biology and Physiology|chapter-url=https://books.google.com/books?id=F-jp8kwcHiAC|year=2012|publisher=Academic Press|isbn=978-0-12-394620-1|pages=353–81|chapter=Analysis of Aging in ''Caenorhabditis elegans''}}</ref> Most known mutations and RNA interference targets that extend lifespan were first discovered in ''C. elegans''.<ref name="Reis2009">{{cite journal | vauthors = Shmookler Reis RJ, Bharill P, Tazearslan C, Ayyadevara S | title = Extreme-longevity mutations orchestrate silencing of multiple signaling pathways | journal = Biochimica et Biophysica Acta (BBA) - General Subjects | volume = 1790 | issue = 10 | pages = 1075–83 | date = October 2009 | pmid = 19465083 | pmc = 2885961 | doi = 10.1016/j.bbagen.2009.05.011 }}</ref>
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The first posits that aging is programmed and therefore follows an inexorable path, a biological timetable, perhaps one that might be a continuation of that which regulates childhood growth and development. This regulation would depend on changes in [[gene]] expression that affect the systems responsible for maintenance, repair, and defense responses. Programmed aging should not be confused with programmed cell death ([[apoptosis]]).  
  
The factors proposed to influence biological aging<ref>{{cite web | title = Mitochondrial Theory of Aging and Other Aging Theories | publisher = 1Vigor | url = http://www.1vigor.com/science/mitochondrial-theory/ | access-date = 4 October 2013 }}</ref> fall into two main categories, ''programmed'' and ''damage-related''. Programmed factors follow a biological timetable, perhaps one that might be a continuation of the one that regulates childhood growth and development. This regulation would depend on changes in gene expression that affect the systems responsible for maintenance, repair and defense responses. Damage-related factors include internal and environmental assaults to living organisms that induce cumulative damage at various levels.<ref name="KunlinJin2010">{{cite journal | vauthors = Jin K | title = Modern Biological Theories of Aging | journal = Aging and Disease | volume = 1 | issue = 2 | pages = 72–74 | date = October 2010 | pmid = 21132086 | pmc = 2995895 }}</ref> A third, novel, concept is that aging is mediated by [[Virtuous circle and vicious circle|vicious cycles]].<ref name="Aleksey V 2018">{{cite journal | vauthors = Belikov AV | title = Age-related diseases as vicious cycles | journal = Ageing Research Reviews | volume = 49 | pages = 11–26 | date = January 2019 | pmid = 30458244 | doi = 10.1016/j.arr.2018.11.002 | s2cid = 53567141 }}</ref>
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The second category of theories suggests various sources and targets of damage that lead to aging. Damage-related factors include internal and environmental assaults to living organisms that induce cumulative damage at various levels.  
  
In a detailed review, Lopez-Otin and colleagues (2013), who discuss ageing through the lens of the damage theory, propose nine metabolic "hallmarks" of ageing in various organisms but especially mammals:<ref name="Lopez-Otin2013">{{cite journal | vauthors = López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G | title = The hallmarks of aging | journal = Cell | volume = 153 | issue = 6 | pages = 1194–217 | date = June 2013 | pmid = 23746838 | pmc = 3836174 | doi = 10.1016/j.cell.2013.05.039 }}</ref>
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A third, novel concept is that aging is mediated by [[Virtuous circle and vicious circle|vicious cycles]].<ref>Aleksey V. Belikov, [https://pubmed.ncbi.nlm.nih.gov/30458244/ Age-related diseases as vicious cycles] ''Ageing Research Reviews'' 49 (January 2019): 11–26. Retrieved May 31, 2022.</ref>
* genomic instability (mutations accumulated in nuclear DNA, in mtDNA, and in the nuclear lamina)
 
* telomere attrition (the authors note that artificial telomerase confers non-cancerous immortality to otherwise mortal cells)
 
* epigenetic alterations (including DNA methylation patterns, post-translational modification of histones, and chromatin remodelling)
 
* loss of [[proteostasis]] (protein folding and proteolysis)
 
* deregulated nutrient sensing (relating to the [[Insulin-like growth factor 1#Aging|Growth hormone/Insulin-like growth factor 1 signalling pathway]], which is the most conserved ageing-controlling pathway in evolution and among its targets are the [[FOXO]]3/[[Sirtuin]] transcription factors and the [[mTOR]] complexes, probably responsive to [[caloric restriction]])
 
* mitochondrial dysfunction (the authors point out however that a causal link between ageing and increased mitochondrial production of reactive oxygen species is no longer supported by recent research)
 
* cellular senescence (accumulation of no longer dividing cells in certain tissues, a process induced especially by [[P16|p16INK4a]]/Rb and p19ARF/[[p53]] to stop cancerous cells from proliferating)
 
* stem cell exhaustion (in the authors' view caused by damage factors such as those listed above)
 
* altered intercellular communication (encompassing especially inflammation but possibly also other intercellular interactions)
 
  
There are three main metabolic pathways which can influence the rate of ageing:
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Additionally, there can be other reasons which can speed up the rate of aging in organisms including human beings, such as obesity and compromised [[immune system]].
* the [[FOXO3]]/[[Sirtuin]] pathway, probably responsive to [[caloric restriction]]
 
* the [[Insulin-like growth factor 1#Aging|Growth hormone/Insulin-like growth factor 1 signalling pathway]]
 
* the activity levels of the [[electron transport chain]] in mitochondria<ref>{{cite journal | vauthors = Berdyshev GD, Korotaev GK, Boiarskikh GV, Vaniushin BF | title = Molecular Biology of Aging | journal = Cell | volume = 96 | issue = 2 | pages = 347–62 | year = 2008 | pmid = 9988222 | doi = 10.1016/s0092-8674(00)80567-x | publisher = Cold Spring Harbor | isbn = 978-0-87969-824-9 | s2cid = 17724023 }}</ref> and (in plants) in chloroplasts.
 
  
It is likely that most of these pathways affect ageing separately, because targeting them simultaneously leads to additive increases in lifespan.<ref name="Taylor2011">{{cite journal | vauthors = Taylor RC, Dillin A | title = Aging as an event of proteostasis collapse | journal = Cold Spring Harbor Perspectives in Biology | volume = 3 | issue = 5 | pages = a004440 | date = May 2011 | pmid = 21441594 | pmc = 3101847 | doi = 10.1101/cshperspect.a004440 }}</ref>
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===Programmed factors===
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The programmed approach suggests three major mechanisms which control aging:<ref name=Jin>Kunlin Jin, [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2995895/ Modern Biological Theories of Aging] ''Aging Dis.'' 1(2) (October 2010): 72–74. Retrieved May 31, 2022.</ref>
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;Programmed Longevity
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Aging is the result of a sequential switching on and off of certain [[gene]]s, with senescence being defined as the time when age-associated deficits are manifested.
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;Endocrine Theory
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Biological clocks act through [[hormone]]s to control the pace of aging.
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;Immunological Theory
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The [[immune system]] is programmed to decline over time, which leads to an increased vulnerability to infectious [[disease]]s and thus aging and death.
  
===Programmed factors===
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The rate of aging varies substantially across different species, and this, to a large extent, is genetically based. For example, numerous [[perennial plant]]s ranging from [[strawberry|strawberries]] and [[potato]]es to [[willow]] trees typically produce [[clone]]s of themselves by [[vegetative reproduction]] and are thus potentially immortal, while [[annual plants]] such as [[wheat]] and [[watermelon]]s die each year and reproduce by sexual reproduction. The oldest [[animal]]s known so far are 15,000-year-old [[Antarctica|Antarctic]] [[sponge]]s,<ref>Marnie Chesterton, [https://www.bbc.com/news/science-environment-40224991 The oldest living thing on Earth] ''BBC News'', June 12, 2017. Retrieved May 31, 2022.</ref> which can reproduce both sexually and clonally.
The rate of ageing varies substantially across different species, and this, to a large extent, is genetically based. For example, numerous [[perennial plant]]s ranging from strawberries and potatoes to [[Willow#Cultivation|willow trees]] typically produce clones of themselves by [[vegetative reproduction]] and are thus potentially immortal, while [[annual plants]] such as wheat and watermelons die each year and reproduce by sexual reproduction. In 2008 it was discovered that inactivation of only two genes in the annual plant ''Arabidopsis thaliana'' leads to its conversion into a potentially immortal perennial plant.<ref>{{cite journal | vauthors = Melzer S, Lens F, Gennen J, Vanneste S, Rohde A, Beeckman T | title = Flowering-time genes modulate meristem determinacy and growth form in Arabidopsis thaliana | journal = Nature Genetics | volume = 40 | issue = 12 | pages = 1489–92 | date = December 2008 | pmid = 18997783 | doi = 10.1038/ng.253 | url = http://www.repository.naturalis.nl/record/429531 | s2cid = 13225884 }}</ref> The oldest animals known so far are 15,000-year-old Antarctic [[sponge]]s,<ref name=BBC2017-OldestLivingThing>{{Cite news|last1=Chesterton|first1=Marnie| name-list-style = vanc |title=The oldest living thing on Earth|url=https://www.bbc.com/news/science-environment-40224991|access-date=16 September 2017|date=12 June 2017|work=BBC News}}</ref> which can reproduce both sexually and clonally.
 
  
Clonal immortality apart, there are certain species whose individual lifespans stand out among Earth's life-forms, including the [[bristlecone pine]] at 5062 years<ref name=oldest>{{cite web|url=http://www.rmtrr.org/oldlist.htm|title=Oldlist|publisher=Rocky Mountain Tree Ring Research|access-date=2016-08-12}}</ref> or 5067 years,<ref name=BBC2017-OldestLivingThing/> invertebrates like the [[hard clam]] (known as ''quahog'' in New England) at 508 years,<ref name="Sosnowska2014">{{cite journal | vauthors = Sosnowska D, Richardson C, Sonntag WE, Csiszar A, Ungvari Z, Ridgway I | title = A heart that beats for 500 years: age-related changes in cardiac proteasome activity, oxidative protein damage and expression of heat shock proteins, inflammatory factors, and mitochondrial complexes in Arctica islandica, the longest-living noncolonial animal | journal = The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences | volume = 69 | issue = 12 | pages = 1448–61 | date = December 2014 | pmid = 24347613 | pmc = 4271020 | doi = 10.1093/gerona/glt201 }}</ref> the [[Greenland shark]] at 400 years,<ref name="Nielsen2016">{{cite journal | vauthors = Nielsen J, Hedeholm RB, Heinemeier J, Bushnell PG, Christiansen JS, Olsen J, Ramsey CB, Brill RW, Simon M, Steffensen KF, Steffensen JF | display-authors = 6 | title = Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus) | journal = Science | volume = 353 | issue = 6300 | pages = 702–4 | date = August 2016 | pmid = 27516602 | doi = 10.1126/science.aaf1703 | url = https://ora.ox.ac.uk/objects/uuid:6c040460-9519-4720-9669-9911bdd03b09 | s2cid = 206647043 | bibcode = 2016Sci...353..702N }}</ref> various deep-sea [[tube worms]] at over 300 years,<ref name="Durkin2017">{{cite journal | vauthors = Durkin A, Fisher CR, Cordes EE | title = Extreme longevity in a deep-sea vestimentiferan tubeworm and its implications for the evolution of life history strategies | journal = Die Naturwissenschaften | volume = 104 | issue = 7–8 | pages = 63 | date = August 2017 | pmid = 28689349 | doi = 10.1007/s00114-017-1479-z | s2cid = 11287549 | bibcode = 2017SciNa.104...63D }}</ref> fish like the [[sturgeon]] and the [[Sebastes|rockfish]], and the [[sea anemone]]<ref>Timiras, Paola S. (2003) ''Physiological Basis of Ageing and Geriatrics''. Informa Health Care. {{ISBN|0-8493-0948-4}}. p. 26.</ref> and [[lobster]].<ref>{{cite web |url=http://animals.howstuffworks.com/marine-life/400-pound-lobster.htm/printable |title=Is there a 400 pound lobster out there? | vauthors = Silverman J |publisher=[[howstuffworks]]|date=2007-07-05 }}</ref><ref>{{cite book |title=Consider the Lobster and Other Essays | vauthors = Wallace DF |publisher=[[Little, Brown & Company]] |year=2005 |isbn=978-0-316-15611-0|title-link=Consider the Lobster }}{{page needed|date=November 2013}}</ref> Such organisms are sometimes said to exhibit [[negligible senescence]].<ref>{{cite journal | vauthors = Guerin JC | title = Emerging area of aging research: long-lived animals with "negligible senescence" | journal = Annals of the New York Academy of Sciences | volume = 1019 | issue = 1 | pages = 518–20 | date = June 2004 | pmid = 15247078 | doi = 10.1196/annals.1297.096 | bibcode = 2004NYASA1019..518G | s2cid = 6418634 }}</ref> The genetic aspect has also been demonstrated in studies of human [[Research into centenarians|centenarians]].
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Clonal immortality apart, there are certain species whose individual lifespans stand out among Earth's life-forms, including the [[bristlecone pine]] at around 5,000 years<ref>[http://www.rmtrr.org/oldlist.htm Oldlist] ''Rocky Mountain Tree Ring Research''. Retrieved May 31, 2022.</ref> invertebrates like the [[hard clam]] (known as ''quahog'' in New England) at 508 years,<ref>Danuta Sosnowska, Chris Richardson, William E. Sonntag, Anna Csiszar, Zoltan Ungvari, and Iain Ridgway, [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4271020/ A heart that beats for 500 years] ''The Journals of Gerontology Series A, Biological Sciences and Medical Sciences'' 69(12) (December 2014): 1448–1461. Retrieved May 31, 2022. </ref> the [[Greenland shark]] at 400 years,<ref>J. Nielsen, ''et al'', [https://ora.ox.ac.uk/objects/uuid:6c040460-9519-4720-9669-9911bdd03b09 Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus)] ''Science'' 353(6300) (August 2016): 702–704. Retrieved May 31, 2022.</ref> various deep-sea [[tube worms]] at over 300 years,<ref>Alanna Durkin, Charles R. Fisher, Erik E. Cordes, [https://link.springer.com/article/10.1007/s00114-017-1479-z Extreme longevity in a deep-sea vestimentiferan tubeworm and its implications for the evolution of life history strategies] ''The Science of Nature'' 104(7–8) (August 2017): 63. Retrieved May 31, 2022. </ref> and [[lobster]]s.<ref>Jacob Silverman, [https://animals.howstuffworks.com/marine-life/400-pound-lobster.htm Is there a 400 pound lobster out there?] ''How Stuff Works''. Retrieved May 31, 2022. </ref> Such organisms are sometimes said to exhibit [[negligible senescence]].<ref>John C. Guerin, [https://pubmed.ncbi.nlm.nih.gov/15247078/ Emerging area of aging research: long-lived animals with "negligible senescence"] ''Annals of the New York Academy of Sciences'' 1019(1) (June 2004): 518–520. Retrieved May 31, 2022. </ref>  
  
* [[Evolution of aging|Evolution of ageing]]: Many have argued that life span, like other [[phenotypes]], is [[natural selection|selected]]. Traits that benefit early survival and reproduction will be [[natural selection|selected]] for even if they contribute to an earlier death. Such a genetic effect is called the [[Antagonistic pleiotropy hypothesis|antagonistic pleiotropy]] effect when referring to a gene (pleiotropy signifying the gene has a double function – enabling reproduction at a young age but costing the organism life expectancy in old age) and is called the [[Evolution of aging|disposable soma]] effect when referring to an entire genetic programme (the organism diverting limited resources from maintenance to reproduction).<ref name="Williams1957"/> The biological mechanisms which regulate lifespan evolved several hundred million years ago.<ref name="Reis2009" />
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[[File:Habibaadansalat.jpg|thumb|right|350px|An elderly [[Somali people|Somali]] woman]]
** Some evidence is provided by oxygen-deprived bacterial cultures.<ref>{{cite journal | vauthors = Nyström T | title = The free-radical hypothesis of aging goes prokaryotic | journal = Cellular and Molecular Life Sciences | volume = 60 | issue = 7 | pages = 1333–41 | date = July 2003 | pmid = 12943222 | doi = 10.1007/s00018-003-2310-X | s2cid = 8406111 }}</ref>
 
** The theory would explain why the [[Dominance (genetics)|autosomal dominant]] disease, [[Huntington's disease]], can persist even though it is inexorably lethal. Also, it has been suggested that some of the genetic variants that increase fertility in the young increase cancer risk in the old.  Such variants occur in genes p53<ref name="Kang 2009">{{cite journal | vauthors = Kang HJ, Feng Z, Sun Y, Atwal G, Murphy ME, Rebbeck TR, Rosenwaks Z, Levine AJ, Hu W | display-authors = 6 | title = Single-nucleotide polymorphisms in the p53 pathway regulate fertility in humans | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 106 | issue = 24 | pages = 9761–6 | date = June 2009 | pmid = 19470478 | pmc = 2700980 | doi = 10.1073/pnas.0904280106 | bibcode = 2009PNAS..106.9761K }}</ref> and BRCA1.<ref name="Smith 2012">{{cite journal | vauthors = Smith KR, Hanson HA, Mineau GP, Buys SS | title = Effects of BRCA1 and BRCA2 mutations on female fertility | journal = Proceedings. Biological Sciences | volume = 279 | issue = 1732 | pages = 1389–95 | date = April 2012 | pmid = 21993507 | pmc = 3282366 | doi = 10.1098/rspb.2011.1697 }}</ref>
 
** The [[reproductive-cell cycle theory]] argues that ageing is regulated specifically by reproductive hormones that act in an antagonistic [[pleiotropic]] manner via cell cycle signalling, promoting growth and development early in life to achieve reproduction, but becoming dysregulated later in life, driving senescence (dyosis) in a futile attempt to maintain reproductive ability.<ref name="Bowen 2004">{{cite journal | vauthors = Bowen RL, Atwood CS | title = Living and dying for sex. A theory of aging based on the modulation of cell cycle signaling by reproductive hormones | journal = Gerontology | volume = 50 | issue = 5 | pages = 265–90 | year = 2004 | pmid = 15331856 | doi = 10.1159/000079125 | s2cid = 18109386 }}</ref><ref name="pmid20851172">{{cite journal | vauthors = Atwood CS, Bowen RL | title = The reproductive-cell cycle theory of aging: an update | journal = Experimental Gerontology | volume = 46 | issue = 2–3 | pages = 100–7 | year = 2011 | pmid = 20851172 | doi = 10.1016/j.exger.2010.09.007 | s2cid = 20998909 }}</ref> The endocrine dyscrasia that follows the loss of follicles with menopause, and the loss of Leydig and Sertoli cells during andropause, drive aberrant cell cycle signalling that leads to cell death and dysfunction, tissue dysfunction (disease) and ultimately death. Moreover, the hormones that regulate reproduction also regulate cellular metabolism, explaining the increases in fat deposition during pregnancy through to the deposition of centralised adiposity with the dysregulation of the HPG axis following menopause and during andropause (Atwood and Bowen, 2004). This theory, which introduced a new definition of ageing, has facilitated the conceptualisation of why and how ageing occurs at the evolutionary, physiological and molecular levels.<ref name="Bowen 2004"/>
 
* Autoimmunity: The idea that ageing results from an increase in [[autoantibodies]] that attack the body's tissues. A number of diseases associated with ageing, such as [[atrophic gastritis]] and [[Hashimoto's thyroiditis]], are probably autoimmune in this way. However, while inflammation is very much evident in old mammals, even completely [[Severe combined immunodeficiency#SCID in animals|immunodeficient]] mice raised in [[Specific-pathogen-free|pathogen-free]] laboratory conditions still experience senescence.{{citation needed|date=August 2016}}
 
[[File:Habibaadansalat.jpg|thumb|right|300px|An elderly [[Somali people|Somali]] woman]]
 
* The cellular balance between energy generation and consumption (energy homeostasis) requires tight regulation during ageing. In 2011, it was demonstrated that acetylation levels of [[AMP-activated protein kinase]] change with age in yeast and that preventing this change slows yeast ageing.<ref name="Mair2011">{{cite journal | vauthors = Mair W, Steffen KK, Dillin A | title = SIP-ing the elixir of youth | journal = Cell | volume = 146 | issue = 6 | pages = 859–60 | date = September 2011 | pmid = 21925309 | doi = 10.1016/j.cell.2011.08.026 | doi-access = free }}</ref>
 
* Skin ageing is caused in part by [[TGF-β]], which reduces the subcutaneous fat that gives skin a pleasant appearance and texture.  [[TGF-β]] does this by blocking the conversion of [[dermal fibroblasts]] into [[fat cells]]; with fewer fat cells underneath to provide support, the skin becomes saggy and wrinkled.  Subcutaneous fat also produces [[cathelicidin]], which is a [[peptide]] that fights bacterial infections.<ref>{{Cite press release |title = UC San Diego Researchers Identify How Skin Ages, Loses Fat and Immunity |url = https://ucsdnews.ucsd.edu/pressrelease/uc_san_diego_researchers_identify_how_skin_ages_loses_fat_and_immunity |date = 2018-12-26 |first = Yadira | last = Galindo | publisher = University of California San Diego}}</ref><ref>{{cite journal | vauthors = Zhang LJ, Chen SX, Guerrero-Juarez CF, Li F, Tong Y, Liang Y, Liggins M, Chen X, Chen H, Li M, Hata T, Zheng Y, Plikus MV, Gallo RL | display-authors = 6 | title = Age-Related Loss of Innate Immune Antimicrobial Function of Dermal Fat Is Mediated by Transforming Growth Factor Beta | journal = Immunity | volume = 50 | issue = 1 | pages = 121–136.e5 | date = January 2019 | pmid = 30594464 | pmc = 7191997 | doi = 10.1016/j.immuni.2018.11.003 | url = | doi-access = free }}</ref>
 
  
 
===Damage-related factors===
 
===Damage-related factors===
* [[DNA damage theory of aging|DNA damage theory of ageing]]: DNA damage is thought to be the common basis of both cancer and ageing, and it has been argued that intrinsic causes of [[DNA damage (naturally occurring)|DNA damage]] are the most important drivers of ageing.<ref>{{cite journal | vauthors = Gensler HL, Bernstein H | title = DNA damage as the primary cause of aging | journal = The Quarterly Review of Biology | volume = 56 | issue = 3 | pages = 279–303 | date = September 1981 | pmid = 7031747 | doi = 10.1086/412317 | jstor = 2826464 | s2cid = 20822805 }}</ref><ref>{{cite journal | vauthors = Sinha JK, Ghosh S, Swain U, Giridharan NV, Raghunath M | title = Increased macromolecular damage due to oxidative stress in the neocortex and hippocampus of WNIN/Ob, a novel rat model of premature aging | journal = Neuroscience | volume = 269 | pages = 256–64 | date = June 2014 | pmid = 24709042 | doi = 10.1016/j.neuroscience.2014.03.040 | s2cid = 9934178 }}</ref><ref>{{cite journal | vauthors = Freitas AA, de Magalhães JP | title = A review and appraisal of the DNA damage theory of ageing | journal = Mutation Research | volume = 728 | issue = 1–2 | pages = 12–22 | year = 2011 | pmid = 21600302 | doi = 10.1016/j.mrrev.2011.05.001 }}</ref> Genetic damage (aberrant structural alterations of the DNA), [[mutation]]s (changes in the DNA sequence), and epimutations ([[Cancer epigenetics#DNA methylation|methylation of gene promoter regions]] or alterations of the [[Cancer epigenetics#Histone modification|DNA scaffolding]] which [[Regulation of gene expression|regulate gene expression]]), can cause abnormal gene expression. DNA damage causes the cells to stop dividing or induces [[apoptosis]], often [[Stem cell theory of aging|affecting stem cell pools]] and hence hindering regeneration. However, lifelong studies of mice suggest that most mutations happen during embryonic and childhood development, when cells divide often, as each cell division is a chance for errors in DNA replication.<ref>{{cite journal | vauthors = Robert L, Labat-Robert J, Robert AM | title = Genetic, epigenetic and posttranslational mechanisms of aging | journal = Biogerontology | volume = 11 | issue = 4 | pages = 387–99 | date = August 2010 | pmid = 20157779 | doi = 10.1007/s10522-010-9262-y | s2cid = 21455794 }}</ref>
+
Numerous damage-related factors have been proposed that lead to aging, including the following:<ref name=Jin/>
* [[Genetic instability]]: Dogs annually lose approximately 3.3% of the DNA in their heart muscle cells while humans lose approximately 0.6% of their heart muscle DNA each year.  These numbers are close to the ratio of the maximum longevities of the two species (120 years vs. 20 years, a 6/1 ratio).  The comparative percentage is also similar between the dog and human for yearly DNA loss in the brain and lymphocytes.  As stated by lead author, [[Bernard L. Strehler]], "...&nbsp;genetic damage (particularly gene loss) is almost certainly (or probably the) central cause of ageing."<ref>{{cite journal | vauthors = Strehler BL | title = Genetic instability as the primary cause of human aging | journal = Experimental Gerontology | volume = 21 | issue = 4–5 | pages = 283–319 | year = 1986 | pmid = 3545872 | doi = 10.1016/0531-5565(86)90038-0 | s2cid = 34431271 }}</ref>
+
;Wear and tear theory  
* Accumulation of waste:
+
Cells and tissues have vital parts that wear out resulting in aging. Like components of an aging machine, parts of the body eventually wear out from repeated use, leading to cell death and inability to function.  
** A buildup of waste products in cells presumably interferes with metabolism. For example, a waste product called [[lipofuscin]] is formed by a complex reaction in cells that binds fat to proteins. This waste accumulates in the cells as small granules, which increase in size as a person ages.<ref>{{cite book | vauthors = Gavrilov LA, Gavrilova NA | date = 2006 | chapter = Reliability Theory of Aging and Longevity | pages = 3–42 | title = Handbook of the Biology of Aging | veditors = Masoro EJ, Austad SN | publisher = Academic Press | location = San Diego, CA }}</ref>
 
** The hallmark of ageing yeast cells appears to be overproduction of certain proteins.<ref name="Janssens 2015"/>
 
** [[Autophagy]] induction can enhance clearance of toxic intracellular waste associated with neurodegenerative diseases and has been comprehensively demonstrated to improve lifespan in yeast, worms, flies, rodents and primates. The situation, however, has been complicated by the identification that autophagy up-regulation can also occur during ageing.<ref name="Carroll 2013">{{cite journal | vauthors = Carroll B, Hewitt G, Korolchuk VI | title = Autophagy and ageing: implications for age-related neurodegenerative diseases | journal = Essays in Biochemistry | volume = 55 | pages = 119–31 | year = 2013 | pmid = 24070476 | doi = 10.1042/bse0550119 | s2cid = 1603760 }}</ref> Autophagy is enhanced in obese mice by caloric restriction, exercise, and a low fat diet (but in these mice is evidently not related with the activation of [[AMP-activated protein kinase]], see above).<ref name="Cui 2013">{{cite journal | vauthors = Cui M, Yu H, Wang J, Gao J, Li J | title = Chronic caloric restriction and exercise improve metabolic conditions of dietary-induced obese mice in autophagy correlated manner without involving AMPK | journal = Journal of Diabetes Research | volume = 2013 | pages = 852754 | year = 2013 | pmid = 23762877 | pmc = 3671310 | doi = 10.1155/2013/852754 }}</ref>
 
* Wear-and-tear theory: The very general idea that changes associated with ageing are the result of chance damage that accumulates over time.<ref name="KunlinJin2010"/>
 
* Accumulation of errors: The idea that ageing results from chance events that escape proof reading mechanisms, which gradually damages the genetic code.
 
* [[Heterochromatin]] loss, model of ageing.<ref>{{cite journal | vauthors = Lee JH, Kim EW, Croteau DL, Bohr VA | title = Heterochromatin: an epigenetic point of view in aging | journal = Experimental & Molecular Medicine | pages = 1466–1474 | date = September 2020 | volume = 52 | issue = 9 | pmid = 32887933 | doi = 10.1038/s12276-020-00497-4 | url = https://www.nature.com/articles/s12276-020-00497-4 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Villeponteau B | title = The heterochromatin loss model of aging | journal = Experimental Gerontology | volume = 32 | issue = 4–5 | pages = 383–94 | date = 1997-07-01 | pmid = 9315443 | doi = 10.1016/S0531-5565(96)00155-6 | url = http://www.sciencedirect.com/science/article/pii/S0531556596001556 | series = Proceedings of the Third International Symposium on the Neurobiology and Neuroendocrinology of Aging | s2cid = 29375335 }}</ref><ref>{{cite journal | vauthors = Tsurumi A, Li WX | title = Global heterochromatin loss: a unifying theory of aging? | journal = Epigenetics | volume = 7 | issue = 7 | pages = 680–8 | date = July 2012 | pmid = 22647267 | pmc = 3414389 | doi = 10.4161/epi.20540 }}</ref>
 
* [[Transposable elements]] in genome disintegration as the primary role in the mechanism of ageing.<ref>{{cite journal | vauthors = Sturm Á, Ivics Z, Vellai T | title = The mechanism of ageing: primary role of transposable elements in genome disintegration | journal = Cellular and Molecular Life Sciences | volume = 72 | issue = 10 | pages = 1839–47 | date = May 2015 | pmid = 25837999 | doi = 10.1007/s00018-015-1896-0 | s2cid = 13241098 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Elsner D, Meusemann K, Korb J | title = Longevity and transposon defense, the case of termite reproductives | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 115 | issue = 21 | pages = 5504–5509 | date = May 2018 | pmid = 29735660 | pmc = 6003524 | doi = 10.1073/pnas.1804046115 }}</ref><ref>{{cite journal | vauthors = Sturm Á, Perczel A, Ivics Z, Vellai T | title = The Piwi-piRNA pathway: road to immortality | journal = Aging Cell | volume = 16 | issue = 5 | pages = 906–911 | date = October 2017 | pmid = 28653810 | pmc = 5595689 | doi = 10.1111/acel.12630 }}</ref>
 
* Cross-linkage: The idea that ageing results from accumulation of [[cross-linked]] compounds that interfere with normal cell function.<ref name="Bernstein book" /><ref>{{cite journal | vauthors = Bjorksten J, Tenhu H | title = The crosslinking theory of aging—added evidence | journal = Experimental Gerontology | volume = 25 | issue = 2 | pages = 91–5 | year = 1990 | pmid = 2115005 | doi = 10.1016/0531-5565(90)90039-5 | s2cid = 19115146 }}</ref>
 
* Studies of mtDNA mutator mice have shown that increased levels of somatic mtDNA mutations directly can cause a variety of ageing phenotypes. The authors propose that mtDNA mutations lead to respiratory-chain-deficient cells and thence to apoptosis and cell loss. They cast doubt experimentally however on the common assumption that mitochondrial mutations and dysfunction lead to increased generation of reactive oxygen species (ROS).<ref>{{cite journal | vauthors = Trifunovic A, Larsson NG | title = Mitochondrial dysfunction as a cause of ageing | journal = Journal of Internal Medicine | volume = 263 | issue = 2 | pages = 167–78 | date = February 2008 | pmid = 18226094 | doi = 10.1111/j.1365-2796.2007.01905.x | s2cid = 28396237 | doi-access = free }}</ref>
 
* [[Free-radical theory]]: Damage by [[free radical]]s, or more generally [[reactive oxygen species]] or [[oxidative stress]], create damage that may give rise to the symptoms we recognise as ageing.<ref name="Bernstein book" /><ref>{{cite journal | vauthors = Harman D | title = The aging process | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 78 | issue = 11 | pages = 7124–8 | date = November 1981 | pmid = 6947277 | pmc = 349208 | doi = 10.1073/pnas.78.11.7124 | bibcode = 1981PNAS...78.7124H }}</ref> [[Michael Ristow]]'s group has provided evidence that the effect of calorie restriction may be due to increased formation of [[free radicals]] within the [[mitochondria]], causing a secondary induction of increased [[antioxidant]] defence capacity.<ref>{{cite journal | vauthors = Schulz TJ, Zarse K, Voigt A, Urban N, Birringer M, Ristow M | title = Glucose restriction extends Caenorhabditis elegans life span by inducing mitochondrial respiration and increasing oxidative stress | journal = Cell Metabolism | volume = 6 | issue = 4 | pages = 280–93 | date = October 2007 | pmid = 17908557 | doi = 10.1016/j.cmet.2007.08.011 }}</ref>
 
*[[Mitochondrial theory of ageing]]: [[free radicals]] produced by [[mitochondria]]l activity damage cellular components, leading to ageing.
 
* [[8-Oxo-2'-deoxyguanosine|DNA oxidation]] and caloric restriction: Caloric restriction reduces [[8-Oxo-2'-deoxyguanosine|8-OH-dG]] DNA damage in organs of ageing rats and mice.<ref name="pmid11517304">{{cite journal | vauthors = Hamilton ML, Van Remmen H, Drake JA, Yang H, Guo ZM, Kewitt K, Walter CA, Richardson A | display-authors = 6 | title = Does oxidative damage to DNA increase with age? | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 98 | issue = 18 | pages = 10469–74 | date = August 2001 | pmid = 11517304 | pmc = 56984 | doi = 10.1073/pnas.171202698 | bibcode = 2001PNAS...9810469H }}</ref><ref name="pmid15763395">{{cite journal | vauthors = Wolf FI, Fasanella S, Tedesco B, Cavallini G, Donati A, Bergamini E, Cittadini A | title = Peripheral lymphocyte 8-OHdG levels correlate with age-associated increase of tissue oxidative DNA damage in Sprague-Dawley rats. Protective effects of caloric restriction | journal = Experimental Gerontology | volume = 40 | issue = 3 | pages = 181–8 | date = March 2005 | pmid = 15763395 | doi = 10.1016/j.exger.2004.11.002 | s2cid = 23752647 }}</ref> Thus, reduction of oxidative DNA damage is associated with a slower rate of ageing and increased lifespan.<ref>{{cite journal | vauthors = Anson RM, Bohr VA | title = Mitochondria, oxidative DNA damage, and aging | journal = Journal of the American Aging Association | volume = 23 | issue = 4 | pages = 199–218 | date = October 2000 | pmid = 23604866 | pmc = 3455271 | doi = 10.1007/s11357-000-0020-y }}</ref>  In a 2021 review article, Vijg stated that “Based on an abundance of evidence, [[DNA damage (naturally occurring)|DNA damage]] is now considered as the single most important driver of the degenerative processes that collectively cause aging.”<ref>Vijg J. From DNA damage to mutations: All roads lead to aging. Ageing Res Rev. 2021 Mar 9;68:101316. doi: 10.1016/j.arr.2021.101316. Epub ahead of print. PMID 33711511</ref>
 
  
== Effects ==
+
;Rate of living theory
[[File:Senescence.JPG|thumb|300px|Enlarged ears and noses of old humans are sometimes blamed on continual cartilage growth, but the cause is more probably gravity.<ref name=Guardian2013>{{Cite news|title=Big ears: they really do grow as we age |url=https://www.theguardian.com/lifeandstyle/shortcuts/2013/jul/17/big-ears-grow-as-we-age|access-date=9 September 2016|date=July 2013|id=MeshID:D000375; OMIM:502000| vauthors = Moss S |newspaper=The Guardian}}</ref>]]
+
This suggests that the greater an organism’s rate of [[oxygen]] basal [[metabolism]], the shorter its life span. While helpful, this does not explain maximum life span.  
 +
 
 +
;Cross-linking theory
 +
According to this theory, an accumulation of cross-linked [[protein]]s damages cells and tissues, slowing down bodily processes and resulting in aging.
  
[[File: Age dynamics of the body mass.png|thumb|400px|Age dynamics of the body mass (1, 2) and mass normalized to height (3, 4) of men (1, 3) and women (2, 4).<ref name="Age dynamics">{{cite journal| vauthors = Gerasimov IG, Ignatov DY |title=Age Dynamics of Body Mass and Human Lifespan| journal = Journal of Evolutionary Biochemistry and Physiology | volume = 40 | issue = 3| pages = 343–349|year=2004| doi = 10.1023/B:JOEY.0000042639.72529.e1|s2cid=9070790|url=https://www.researchgate.net/publication/226729610}}</ref>]]
+
;Free radical theory
 +
This proposes that [[free radical]]s cause damage to the macromolecular components of the cell, giving rise to accumulated damage causing cells, and eventually organs, to stop functioning. Macromolecules, such as [[nucleic acid]]s, [[lipid]]s, [[sugar]]s, and [[proteins]], are susceptible to free radical attack. [[Enzyme]]s, which are natural antioxidants, are found in the body and function to curb build-up of free radicals.  
  
[[File:Alzheimer's disease brain comparison.jpg|thumb|400px|Comparison of a normal aged brain (left) and a brain affected by [[Alzheimer's disease]] (right).]]
+
;Somatic DNA damage theory
Ageing increases the [[risk factor|risk]] of [[diseas]]es.
+
[[DNA]] damage occurs continuously in cells of living organisms. While most of the damage is repaired naturally, some accumulates as the repair mechanisms cannot correct defects as fast as they are produced. Thus, aging results from damage to the genetic integrity of the body’s cells.
  
A number of characteristic ageing symptoms are experienced by a majority or by a significant proportion of humans during their lifetimes.
+
Other suggested factors include: progressive loss of physiological integrity through genomic instability (mutations accumulated in nuclear DNA, in mtDNA, and in the nuclear lamina) and [[telomere]] attrition.<ref>Carlos López-Otín, Maria A. Blasco, Linda Partridge, Manuel Serrano, and Guido Kroemer, [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3836174/ The Hallmarks of Aging] ''Cell'' 153(6) (June 2013): 1194–1217. Retrieved May 31, 2022.</ref> Also, accumulation of waste products in cells presumably interferes with [[metabolism]]. For example, a waste product called [[lipofuscin]] is formed by a complex reaction in cells that binds fat to proteins. This waste accumulates in the cells as small granules, which increase in size as a person ages.<ref> Edward J. Masoro  and Steven N. Austad (eds.), ''Handbook of the Biology of Aging'' (Academic Press, 2006, ISBN  0120883872).</ref>
* Teenagers lose the young child's ability to [[Presbycusis|hear]] high-frequency sounds above 20&nbsp;kHz.<ref name=HiFreqAudiometry2014>{{cite journal | vauthors = Rodríguez Valiente A, Trinidad A, García Berrocal JR, Górriz C, Ramírez Camacho R | title = Extended high-frequency (9-20 kHz) audiometry reference thresholds in 645 healthy subjects | journal = International Journal of Audiology | volume = 53 | issue = 8 | pages = 531–45 | date = August 2014 | pmid = 24749665 | doi = 10.3109/14992027.2014.893375 | s2cid = 30960789 }}</ref>
 
* [[Wrinkle]]s develop mainly due to [[photoaging|photoageing]], particularly affecting sun-exposed areas (face).<ref name="Thurstan 2012">{{cite journal | vauthors = Thurstan SA, Gibbs NK, Langton AK, Griffiths CE, Watson RE, Sherratt MJ | title = Chemical consequences of cutaneous photoageing | journal = Chemistry Central Journal | volume = 6 | issue = 1 | pages = 34 | date = April 2012 | pmid = 22534143 | pmc = 3410765 | doi = 10.1186/1752-153X-6-34 }}</ref>
 
* After [[Age and female fertility|peaking in the mid-20s, female fertility]] declines.<ref>{{cite journal|url=https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0076677/|title=Infertility: Overview|last=pmhdev|date=25 March 2015|publisher=Institute for Quality and Efficiency in Health Care (IQWiG)|via=www.ncbi.nlm.nih.gov}}</ref>
 
* After age 30 the mass of human body is decreased until 70 years and then shows damping oscillations.<ref name="Age dynamics"/>
 
* Muscles have reduced capacity of responding to exercise or injury and loss of muscle mass and strength ([[sarcopenia]]) is common.<ref>{{cite journal | vauthors = Ryall JG, Schertzer JD, Lynch GS | title = Cellular and molecular mechanisms underlying age-related skeletal muscle wasting and weakness | journal = Biogerontology | volume = 9 | issue = 4 | pages = 213–28 | date = August 2008 | pmid = 18299960 | doi = 10.1007/s10522-008-9131-0 | s2cid = 8576449 }}</ref> VO2 max and maximum heart rate decline.<ref>{{cite journal | vauthors = Betik AC, Hepple RT | title = Determinants of VO2 max decline with aging: an integrated perspective | journal = Applied Physiology, Nutrition, and Metabolism | volume = 33 | issue = 1 | pages = 130–40 | date = February 2008 | pmid = 18347663 | doi = 10.1139/H07-174 | s2cid = 24468921 }}</ref>
 
*Hand strength and mobility are decreased during the aging process. These things include, "hand and finger strength and ability to control submaximal pinch force and maintain a steady precision pinch posture, manual speed, and hand sensation"<ref>{{Cite journal|last1=Ranganathan|first1=Vinoth K.|last2=Siemionow|first2=Vlodek|last3=Sahgal|first3=Vinod|last4=Yue|first4=Guang H.|date=November 2001|title=Effects of Aging on Hand Function|url=http://dx.doi.org/10.1046/j.1532-5415.2001.4911240.x|journal=Journal of the American Geriatrics Society|volume=49|issue=11|pages=1478–1484|doi=10.1046/j.1532-5415.2001.4911240.x|pmid=11890586|s2cid=22988219|issn=0002-8614}}</ref>
 
* People over 35 years of age are at increasing risk for losing strength in the [[ciliary muscle]] of the eyes which leads to difficulty focusing on close objects, or [[presbyopia]].<ref>{{cite web|title=Facts About Presbyopia|url=https://nei.nih.gov/health/errors/presbyopia|publisher=National Eye Institute|access-date=11 September 2016|location=Last Reviewed October 2010}}</ref><ref name="Weale 2003">{{cite journal | vauthors = Weale RA | title = Epidemiology of refractive errors and presbyopia | journal = Survey of Ophthalmology | volume = 48 | issue = 5 | pages = 515–43 | year = 2003 | pmid = 14499819 | doi = 10.1016/S0039-6257(03)00086-9 }}</ref> Most people experience [[presbyopia]] by age 45–50.<ref name="Truscott 2009">{{cite journal | vauthors = Truscott RJ | title = Presbyopia. Emerging from a blur towards an understanding of the molecular basis for this most common eye condition | journal = Experimental Eye Research | volume = 88 | issue = 2 | pages = 241–7 | date = February 2009 | pmid = 18675268 | doi = 10.1016/j.exer.2008.07.003 }}</ref> The cause is lens hardening by decreasing levels of [[alpha-crystallin]], a process which may be sped up by higher temperatures.<ref name="Truscott 2009"/><ref>{{cite journal | vauthors = Pathai S, Shiels PG, Lawn SD, Cook C, Gilbert C | title = The eye as a model of ageing in translational research—molecular, epigenetic and clinical aspects | journal = Ageing Research Reviews | volume = 12 | issue = 2 | pages = 490–508 | date = March 2013 | pmid = 23274270 | doi = 10.1016/j.arr.2012.11.002 | s2cid = 26015190 }}</ref>
 
* Around age 50, [[Human hair color#Aging or achromotrichia|hair turns grey]].<ref>{{cite journal | vauthors = Pandhi D, Khanna D | title = Premature graying of hair | journal = Indian Journal of Dermatology, Venereology and Leprology | volume = 79 | issue = 5 | pages = 641–53 | date = 2013 | pmid = 23974581 | doi = 10.4103/0378-6323.116733 | doi-access = free }}</ref> [[Pattern hair loss]] by the age of 50 affects about 30–50% of males<ref>{{cite journal | vauthors = Hamilton JB | title = Patterned loss of hair in man; types and incidence | journal = Annals of the New York Academy of Sciences | volume = 53 | issue = 3 | pages = 708–28 | date = March 1951 | pmid = 14819896 | doi = 10.1111/j.1749-6632.1951.tb31971.x | bibcode = 1951NYASA..53..708H | s2cid = 32685699 }}</ref> and a quarter of females.<ref name=Var2015>{{cite journal | vauthors = Vary JC | title = Selected Disorders of Skin Appendages—Acne, Alopecia, Hyperhidrosis | journal = The Medical Clinics of North America | volume = 99 | issue = 6 | pages = 1195–211 | date = November 2015 | pmid = 26476248 | doi = 10.1016/j.mcna.2015.07.003 }}</ref>
 
* [[Menopause]] typically occurs between 44 and 58 years of age.<ref>{{cite journal | vauthors = Morabia A, Costanza MC | title = International variability in ages at menarche, first livebirth, and menopause. World Health Organization Collaborative Study of Neoplasia and Steroid Contraceptives | journal = American Journal of Epidemiology | volume = 148 | issue = 12 | pages = 1195–205 | date = December 1998 | pmid = 9867266 | doi = 10.1093/oxfordjournals.aje.a009609 | doi-access = free }}</ref>
 
*  In the 60–64 age cohort, the incidence of [[osteoarthritis]] rises to 53%. Only 20% however report disabling osteoarthritis at this age.<ref name="Thomas2014">{{cite journal | vauthors = Thomas E, Peat G, Croft P | title = Defining and mapping the person with osteoarthritis for population studies and public health | journal = Rheumatology | volume = 53 | issue = 2 | pages = 338–45 | date = February 2014 | pmid = 24173433 | pmc = 3894672 | doi = 10.1093/rheumatology/ket346 }}</ref>
 
*  Almost half of people older than 75 have [[hearing loss]] (presbycusis) inhibiting spoken communication.<ref>{{cite web|title=Hearing Loss and Older Adults|url=https://www.nidcd.nih.gov/health/hearing-loss-older-adults|publisher=National Institute on Deafness and Other Communication Disorders|access-date=11 September 2016|format=Last Updated 3 June 2016|date=2016-01-26}}</ref> Many vertebrates such as fish, birds and amphibians do not suffer presbycusis in old age as they are able to regenerate their [[cochlea]]r sensory cells, whereas mammals including humans have genetically lost this ability.<ref name="Rubel2013">{{cite journal | vauthors = Rubel EW, Furrer SA, Stone JS | title = A brief history of hair cell regeneration research and speculations on the future | journal = Hearing Research | volume = 297 | pages = 42–51 | date = March 2013 | pmid = 23321648 | pmc = 3657556 | doi = 10.1016/j.heares.2012.12.014 }}</ref>
 
*  By age 80, more than half of all Americans either have a [[cataract]] or have had [[cataract surgery]].<ref name=NIH2009>{{cite web|title=Facts About Cataract|url=https://www.nei.nih.gov/health/cataract/cataract_facts|access-date=14 August 2016|date=September 2015}}</ref>
 
* [[Frailty syndrome|Frailty]], a syndrome of decreased strength, physical activity, physical performance and energy, affects 25% of those over 85.<ref name=Fried_2001>{{cite journal | vauthors = Fried LP, Tangen CM, Walston J, Newman AB, Hirsch C, Gottdiener J, Seeman T, Tracy R, Kop WJ, Burke G, McBurnie MA | display-authors = 6 | title = Frailty in older adults: evidence for a phenotype | journal = The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences | volume = 56 | issue = 3 | pages = M146-56 | date = March 2001 | pmid = 11253156 | doi = 10.1093/gerona/56.3.m146 | citeseerx = 10.1.1.456.139 }}</ref><ref>Percentage derived from Table 2 in Fried et al. 2001</ref>
 
* [[Atherosclerosis]] is classified as an ageing disease.<ref name="Wang 2012">{{cite journal | vauthors = Wang JC, Bennett M | title = Aging and atherosclerosis: mechanisms, functional consequences, and potential therapeutics for cellular senescence | journal = Circulation Research | volume = 111 | issue = 2 | pages = 245–59 | date = July 2012 | pmid = 22773427 | doi = 10.1161/CIRCRESAHA.111.261388 | doi-access = free }}</ref> It leads to cardiovascular disease (for example [[stroke]] and [[Myocardial infarction|heart attack]])<ref name="Wang 2016">{{cite journal | vauthors = Herrington W, Lacey B, Sherliker P, Armitage J, Lewington S | title = Epidemiology of Atherosclerosis and the Potential to Reduce the Global Burden of Atherothrombotic Disease | journal = Circulation Research | volume = 118 | issue = 4 | pages = 535–46 | date = February 2016 | pmid = 26892956 | doi = 10.1161/CIRCRESAHA.115.307611 | doi-access = free }}</ref> which globally is the most common cause of death.<ref>{{cite web |url=https://www.who.int/news-room/fact-sheets/detail/the-top-10-causes-of-death |title=The top 10 causes of death |author=<!--Not stated—> |date=9 December 2020 |publisher=WHO |access-date=11 March 2021}}</ref> Vessel ageing causes vascular remodeling and loss of arterial elasticity and as a result causes the stiffness of the vasculature.<ref name="Wang 2012"/>
 
* Recent evidence suggests that age-related risk of death plateaus after age 105.<ref>{{cite web |url=https://www.webmd.com/healthy-aging/news/20180628/does-human-life-span-really-have-a-limit#1|title=Does Human Life Span Really Have a Limit?|website=WebMD|date=28 June 2018}}</ref> The maximum human lifespan is suggested to be [[Old age|115 years]].<ref name="NYT-20161005">{{cite news |last=Zimmer |first=Carl |author-link=Carl Zimmer |title=What's the Longest Humans Can Live? 115 Years, New Study Says |url=https://www.nytimes.com/2016/10/06/science/maximum-life-span-study.html |date=5 October 2016 |work=[[The New York Times]] |access-date=6 October 2016 }}</ref><ref name="NAT-20151005">{{cite journal | vauthors = Dong X, Milholland B, Vijg J | title = Evidence for a limit to human lifespan | journal = Nature | volume = 538 | issue = 7624 | pages = 257–259 | date = October 2016 | pmid = 27706136 | doi = 10.1038/nature19793 | s2cid = 3623127 | bibcode = 2016Natur.538..257D }}</ref> The oldest reliably recorded human was [[Jeanne Calment]] who died in 1997 at 122.
 
  
[[Dementia]] becomes more common with age.<ref name=Larson2013>{{cite journal | vauthors = Larson EB, Yaffe K, Langa KM | title = New insights into the dementia epidemic | journal = The New England Journal of Medicine | volume = 369 | issue = 24 | pages = 2275–7 | date = December 2013 | pmid = 24283198 | pmc = 4130738 | doi = 10.1056/nejmp1311405 }}</ref> About 3% of people between the ages of 65 and 74, 19% between 75 and 84, and nearly half of those over 85 years of age have dementia.<ref>{{cite book|last1=Umphred|first1=Darcy| name-list-style = vanc |title=Neurological rehabilitation|date=2012|publisher=Elsevier Mosby|location=St. Louis, MO|isbn=978-0-323-07586-2|page=838|edition=6th|url=https://books.google.com/books?id=I9ltC-ZrNOMC&pg=PA838}}</ref> The spectrum ranges from [[mild cognitive impairment]] to the neurodegenerative diseases of [[Alzheimer's disease]], [[cerebrovascular disease]], [[Parkinson's disease]] and [[Lou Gehrig's disease]]. Furthermore, many types of [[Memory and aging|memory decline with ageing]], but not [[semantic memory]] or general knowledge such as vocabulary definitions, which typically increases or remains steady until late adulthood<ref name="Schaie2005">{{cite book|last1=Schaie|first1=K. Warner v|year=2005|doi=10.1093/acprof:oso/9780195156737.001.0001|title=Developmental Influences on Adult Intelligence|isbn=978-0-19-515673-7}}{{page needed|date=November 2013}}</ref> (see [[Aging brain|Ageing brain]]). [[Intelligence]] declines with age, though the rate varies depending on the [[Theory of multiple intelligences|type]] and may in fact remain steady throughout most of the lifespan, dropping suddenly only as people near the end of their lives. Individual variations in rate of cognitive decline may therefore be explained in terms of people having different lengths of life.<ref name=Stuart>{{cite book| vauthors = Stuart-Hamilton I |title=The Psychology of Ageing: An Introduction|publisher=Jessica Kingsley Publishers|location=London|year=2006|isbn=978-1-84310-426-1}}</ref> There are changes to the brain: after 20 years of age there is a 10% reduction each decade in the total length of the brain's [[myelinated]] [[axons]].<ref name="Marner">{{cite journal | vauthors = Marner L, Nyengaard JR, Tang Y, Pakkenberg B | title = Marked loss of myelinated nerve fibers in the human brain with age | journal = The Journal of Comparative Neurology | volume = 462 | issue = 2 | pages = 144–52 | date = July 2003 | pmid = 12794739 | doi = 10.1002/cne.10714 | s2cid = 35293796 }}</ref><ref>{{cite book|chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK3873/|title=Brain Aging: Models, Methods, and Mechanisms| vauthors = Peters A | veditors = Riddle DR |date=1 January 2007|publisher=CRC Press/Taylor & Francis|pmid=21204349|isbn=978-0-8493-3818-2|chapter=The Effects of Normal Aging on Nerve Fibers and Neuroglia in the Central Nervous System|series=Frontiers in Neuroscience}}</ref>
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== Effects ==
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[[File:Senescence.JPG|thumb|300px|Enlarged ears and noses of old humans are sometimes blamed on continual cartilage growth, but the cause is more probably gravity.<ref>Stephen Moss, [https://www.theguardian.com/lifeandstyle/shortcuts/2013/jul/17/big-ears-grow-as-we-age Big ears: they really do grow as we age] ''The Guardian'', July 17, 2013. Retrieved May 31, 2022. </ref>]]
  
Age can result in [[visual impairment]], whereby [[non-verbal communication]] is reduced,<ref>{{cite book | vauthors = Worrall L, Hickson LM | date = 2003 | chapter = Theoretical foundations of communication disability in aging | title = Communication disability in aging: from prevention to intervention | pages = 32–33 | veditors  = Worrall L, Hickson LM | location = Clifton Park, NY | publisher = Delmar Learning }}</ref> which can lead to isolation and possible depression. Older adults, however, may not suffer depression as much as younger adults, and were paradoxically found to have improved mood despite declining physical health.<ref>{{cite journal | vauthors = Lys R, Belanger E, Phillips SP | title = Improved mood despite worsening physical health in older adults: Findings from the International Mobility in Aging Study (IMIAS) | journal = PLOS ONE | volume = 14 | issue = 4 | pages = e0214988 | date = April 2019 | pmid = 30958861 | pmc = 6453471 | doi = 10.1371/journal.pone.0214988 | bibcode = 2019PLoSO..1414988L }}</ref> [[Macular degeneration]] causes vision loss and increases with age, affecting nearly 12% of those above the age of 80.<ref name="Meh2015">{{cite journal | vauthors = Mehta S | title = Age-Related Macular Degeneration | journal = Primary Care | volume = 42 | issue = 3 | pages = 377–91 | date = September 2015 | pmid = 26319344 | doi = 10.1016/j.pop.2015.05.009 }}</ref> This degeneration is caused by systemic changes in the circulation of waste products and by growth of abnormal vessels around the retina.<ref name="Nussbaum, J. F. 1989">{{cite book | vauthors = Nussbaum JF, Thompson TL, Robinson JD | date = 1989 | chapter = Barriers to conversation | pages = 234–53 | veditors = Nussbaum JF, Thompson TL, Robinson JD | title = Communication and aging | location = New York | publisher = Harper & Row }}</ref>
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[[File: Age dynamics of the body mass.png|thumb|400px|Age dynamics of the body mass (1, 2) and mass normalized to height (3, 4) of men (1, 3) and women (2, 4).<ref name="Age dynamics">I. G. Gerasimov and Dmitry Yu Ignatov, [https://www.researchgate.net/publication/226729610_Age_Dynamics_of_Body_Mass_and_Human_Lifespan Age Dynamics of Body Mass and Human Lifespan] ''Journal of Evolutionary Biochemistry and Physiology'' 40(3) (2004):343–349. Retrieved May 31, 2022.</ref>]]
  
Other visual diseases that often appear with age would be cataracts and glaucoma. A cataract occurs when the lens of the eye becomes cloudy making vision blurry and eventually causing blindness if untreated.<ref>{{Cite web|title=Cataracts {{!}} National Eye Institute|url=https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/cataracts|access-date=2021-07-03|website=www.nei.nih.gov}}</ref> They develop over time and are seen most often with those that are older. Cataracts can be treated through surgery. Glaucoma is another common visual disease that appears in older adults. Glaucoma is caused by damage to the optic nerve causing vision loss.<ref>{{Cite web|title=Glaucoma {{!}} National Eye Institute|url=https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/glaucoma|access-date=2021-07-03|website=www.nei.nih.gov}}</ref> Glaucoma usually develops over time but there are variations to glaucoma, and some have sudden onset. There are a few procedures for glaucoma but there is no cure or fix for the damage once it has happened. Prevention is the best measure in the case of glaucoma.<ref>{{Cite web|title=Glaucoma {{!}} National Eye Institute|url=https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/glaucoma|access-date=2021-07-03|website=www.nei.nih.gov}}</ref>
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[[File:Alzheimer's disease brain comparison.jpg|thumb|400px|Comparison of a normal aged brain (left) and a brain affected by [[Alzheimer's disease]] (right).]]
  
A distinction can be made between "proximal ageing" (age-based effects that come about because of factors in the recent past) and "distal ageing" (age-based differences that can be traced to a cause in a person's early life, such as childhood [[poliomyelitis]]).<ref name=Stuart/>
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In humans, aging represents the accumulation of changes in a [[human being]] over time and can encompass [[Human body|physical]], [[psychological]], and social changes. Reaction time, for example, may slow with age, while memories and general knowledge typically increase. Aging also increases the [[risk factor|risk]] of [[disease]]s.
  
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A number of characteristic aging symptoms are experienced by a significant proportion of human beings during their lifetimes, including the following:
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* After peaking in the mid-20s, female [[fertility]] declines.<ref>[https://www.ncbi.nlm.nih.gov/books/NBK293711/ Infertility: Overview] ''Institute for Quality and Efficiency in Health Care'', March 25, 2015. Retrieved May 31, 2022.</ref>
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* After age 30 the mass of human body is decreased until 70 years and then shows damping oscillations.<ref name="Age dynamics"/>
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* Muscles have reduced capacity of responding to exercise or injury and loss of muscle mass and strength ([[sarcopenia]]) is common.<ref>James G. Ryall, Jonathan D. Schertzer, and Gordon S. Lynch, [https://pubmed.ncbi.nlm.nih.gov/18299960/ Cellular and molecular mechanisms underlying age-related skeletal muscle wasting and weakness] ''Biogerontology'' 9(4) (August 2008): 213–228. Retrieved May 31, 2022. </ref>
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*Hand strength and mobility are decreased during the aging process. These things include "hand and finger strength and ability to control submaximal pinch force and maintain a steady precision pinch posture, manual speed, and hand sensation."<ref>Vinoth K. Ranganathan, Vlodek Siemionow, Vinod Sahgal, and Guang H. Yue, [https://agsjournals.onlinelibrary.wiley.com/doi/abs/10.1046/j.1532-5415.2001.4911240.x Effects of Aging on Hand Function] ''Journal of the American Geriatrics Society'' 49(11) (November 2001):1478–1484. Retrieved May 31, 2022.</ref>
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* People over 35 years of age are at increasing risk for losing strength in the [[ciliary muscle]] of the [[eye]]s which leads to difficulty focusing on close objects, or [[presbyopia]].<ref>[https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/refractive-errors Refractive Errors] ''National Eye Institute''. Retrieved May 31, 2022.</ref> Most people experience [[presbyopia]] by age 45–50.
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* Around age 50, [[hair]] turns grey. [[Pattern hair loss]] or [[baldness]] by the age of 50 affects about 50 percent of men and 25 percent of women.
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* [[Menopause]] typically occurs between 44 and 58 years of age.
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* In the 60–64 age cohort, the incidence of [[osteoarthritis]] rises.
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* [[Wrinkle]]s develop mainly due to [[photoaging|photoageing]], particularly affecting sun-exposed areas (face).
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*  Almost half of people older than 75 have [[hearing loss]] (presbycusis) inhibiting spoken communication.<ref>[https://www.nidcd.nih.gov/health/hearing-loss-older-adults Hearing Loss and Older Adults] ''National Institute on Deafness and Other Communication Disorders''. Retrieved May 31, 2022.</ref>
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*  By age 80, more than half of all Americans either have a [[cataract]] or have had [[cataract surgery]].<ref>[https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/cataracts Cataracts] ''National Eye Institute''. Retrieved May 31, 2022.</ref>
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* [[Frailty syndrome|Frailty]], a syndrome of decreased strength, physical activity, physical performance and energy, affects 25 percent of those over 85.<ref>L.P. Fried, C.M. Tangen, J. Walston, A.B. Newman, C. Hirsch, J. Gottdiener, T. Seeman, R. Tracy, W.J. Kop, G. Burke, and M.A. McBurnie, [https://pubmed.ncbi.nlm.nih.gov/11253156/ Frailty in older adults: evidence for a phenotype] ''The Journals of Gerontology Series A, Biological Sciences and Medical Sciences'' 56(3) (March 2001): M146-156. Retrieved May 31, 2022. </ref>
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* [[Atherosclerosis]] is classified as an aging disease, which leads to cardiovascular disease (for example [[stroke]] and [[Myocardial infarction|heart attack]]), globally the most common causes of death.<ref>[https://www.who.int/news-room/fact-sheets/detail/the-top-10-causes-of-death The top 10 causes of death] ''World Health Organization'', December 9, 2020. Retrieved May 31, 2022.</ref>
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*[[Dementia]] becomes more common with age. The spectrum ranges from [[mild cognitive impairment]] to the neurodegenerative diseases of [[Alzheimer's disease]], [[cerebrovascular disease]], [[Parkinson's disease]] and [[Lou Gehrig's disease]].  bout 3 percent of people between the ages of 65 and 74, 19 percent between 75 and 84, and nearly half of those over 85 years of age have dementia.<ref> Rolando T. Lazaro, Sandra G. Reina-Guerra, and Myla Quiben, ''Umphred's Neurological Rehabilitation'' (Mosby, 2019, ISBN 0323611176).</ref> Furthermore, many types of [[Memory and aging|memory decline with aging]], but not [[semantic memory]] or general knowledge such as vocabulary definitions, which typically increases or remains steady until late adulthood.<ref>K. Warner Schaie, ''Developmental Influences on Adult Intelligence'' (Oxford University Press, 2012, ISBN 0195386132). </ref> Individual variations in rate of cognitive decline may be explained in terms of people having different lengths of life.<ref>Ian Stuart-Hamilton, ''The Psychology of Ageing: An Introduction'' (Jessica Kingsley Publishers, 2012, ISBN 184905245X).</ref>
  
 
== Prevention and delay ==
 
== Prevention and delay ==
 
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Human beings who do not have a belief in an [[afterlife]], the continued existence of an eternal [[spirit]] or [[soul]] after the [[death]] of their physical body, have sought ways to prevent aging and death, or at least to delay the process. Such research supports each individual's likelihood of living their full lifespan in good [[health]]. The following are factors which have been found to increase the length and quality of life.
  
 
===Lifestyle===
 
===Lifestyle===
[[Caloric restriction]] substantially affects lifespan in many animals, including the ability to delay or prevent many age-related diseases.<ref name="Guarente2005">{{cite journal | vauthors = Guarente L, Picard F | title = Calorie restriction—the SIR2 connection | journal = Cell | volume = 120 | issue = 4 | pages = 473–82 | date = February 2005 | pmid = 15734680 | doi = 10.1016/j.cell.2005.01.029 | s2cid = 14245512 }}</ref> Typically, this involves caloric intake of 60–70% of what an ''[[ad libitum#Biology|ad libitum]]'' animal would consume, while still maintaining proper nutrient intake.<ref name="Guarente2005"/> In rodents, this has been shown to increase lifespan by up to 50%;<ref name="Agarwal2011">{{cite journal | vauthors = Agarwal B, Baur JA | title = Resveratrol and life extension | journal = Annals of the New York Academy of Sciences | volume = 1215 | issue = 1 | pages = 138–43 | date = January 2011 | pmid = 21261652 | doi = 10.1111/j.1749-6632.2010.05850.x | bibcode = 2011NYASA1215..138A | s2cid = 41701458 | doi-access = free }}</ref> similar effects occur for yeast and ''Drosophila''.<ref name="Guarente2005"/> No lifespan data exist for humans on a calorie-restricted diet,<ref name="Junnila2013"/> but several reports support protection from age-related diseases.<ref>{{cite journal | vauthors = Larson-Meyer DE, Newcomer BR, Heilbronn LK, [[Júlia Volaufová|Volaufova J]], Smith SR, Alfonso AJ, Lefevre M, Rood JC, Williamson DA, Ravussin E | display-authors = 6 | title = Effect of 6-month calorie restriction and exercise on serum and liver lipids and markers of liver function | journal = Obesity | volume = 16 | issue = 6 | pages = 1355–62 | date = June 2008 | pmid = 18421281 | pmc = 2748341 | doi = 10.1038/oby.2008.201 }}</ref><ref>{{cite journal | vauthors = Heilbronn LK, de Jonge L, Frisard MI, DeLany JP, Larson-Meyer DE, Rood J, Nguyen T, Martin CK, Volaufova J, Most MM, Greenway FL, Smith SR, Deutsch WA, Williamson DA, Ravussin E | display-authors = 6 | title = Effect of 6-month calorie restriction on biomarkers of longevity, metabolic adaptation, and oxidative stress in overweight individuals: a randomized controlled trial | journal = JAMA | volume = 295 | issue = 13 | pages = 1539–48 | date = April 2006 | pmid = 16595757 | pmc = 2692623 | doi = 10.1001/jama.295.13.1539 }}</ref> Two major ongoing studies on [[Rhesus macaque|rhesus monkeys]] initially revealed disparate results; while one study, by the University of Wisconsin, showed that caloric restriction does extend lifespan,<ref name = "Colman2009">{{cite journal | vauthors = Colman RJ, Anderson RM, Johnson SC, Kastman EK, Kosmatka KJ, Beasley TM, Allison DB, Cruzen C, Simmons HA, Kemnitz JW, Weindruch R | display-authors = 6 | title = Caloric restriction delays disease onset and mortality in rhesus monkeys | journal = Science | volume = 325 | issue = 5937 | pages = 201–4 | date = July 2009 | pmid = 19590001 | pmc = 2812811 | doi = 10.1126/science.1173635 | bibcode = 2009Sci...325..201C }}</ref> the second study, by the National Institute on Aging (NIA), found no effects of caloric restriction on longevity.<ref>{{cite journal | vauthors = Mattison JA, Roth GS, Beasley TM, Tilmont EM, Handy AM, Herbert RL, Longo DL, Allison DB, Young JE, Bryant M, Barnard D, Ward WF, Qi W, Ingram DK, de Cabo R | display-authors = 6 | title = Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study | journal = Nature | volume = 489 | issue = 7415 | pages = 318–21 | date = September 2012 | pmid = 22932268 | pmc = 3832985 | doi = 10.1038/nature11432 | bibcode = 2012Natur.489..318M }}</ref> Both studies nevertheless showed improvement in a number of health parameters. Notwithstanding the similarly low calorie intake, the diet composition differed between the two studies (notably a high [[sucrose]] content in the Wisconsin study), and the monkeys have different origins (India, China), initially suggesting that genetics and dietary composition, not merely a decrease in calories, are factors in longevity.<ref name="Junnila2013"/> However, in a comparative analysis in 2014, the Wisconsin researchers found that the allegedly non-starved NIA control monkeys in fact are moderately underweight when compared with other monkey populations, and argued this was due to the NIA's apportioned feeding protocol in contrast to Wisconsin's truly unrestricted ''ad libitum'' feeding protocol.<ref name=Colman2014>{{cite journal | vauthors = Colman RJ, Beasley TM, Kemnitz JW, Johnson SC, Weindruch R, Anderson RM | title = Caloric restriction reduces age-related and all-cause mortality in rhesus monkeys | journal = Nature Communications | volume = 5 | pages = 3557 | date = April 2014 | pmid = 24691430 | pmc = 3988801 | doi = 10.1038/ncomms4557 | bibcode = 2014NatCo...5.3557C }}</ref> They conclude that moderate calorie restriction rather than extreme calorie restriction is sufficient to produce the observed health and longevity benefits in the studied rhesus monkeys.<ref>"There may be little advantage of moderate CR over modest CR—this would be an extremely important discovery and one that merits further investigation."</ref>
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A healthy [[diet]] may reduce the effects of aging. For example, the [[Mediterranean diet]] is credited with lowering the risk of heart disease and early death. The major contributors to mortality risk reduction appear to be a higher consumption of vegetables, fish, fruits, nuts, and monounsaturated fatty acids ([[olive]] oil).<ref name>[https://www.sciencedaily.com/releases/2016/08/160829094040.htm Mediterranean diet associated with lower risk of early death in cardiovascular disease patients] ''European Society of Cardiology'', August 29, 2016. Retrieved May 31, 2022. </ref>
 
 
In his book ''How and Why We Age'', Hayflick says that caloric restriction may not be effective in humans, citing data from the Baltimore Longitudinal Study of Aging which shows that being thin does not favour longevity.{{Request quotation|date=February 2013}}<ref name="Hayflick 1994">{{Cite book| last1=Hayflick| first1=Leonard | name-list-style = vanc | title=How and why we age| year=1994| publisher=Ballantine Books| location=New York| isbn=978-0-345-33918-8| oclc=29908633| page=[https://archive.org/details/howwhyweage00hayf/page/261 261]| url-access=registration| url=https://archive.org/details/howwhyweage00hayf/page/261}}</ref> However, there may be confounders, e.g. smoking reduces both appetite and lifespan. Similarly, it is sometimes claimed that moderate ''obesity'' in later life may improve survival, but newer research has identified confounding factors such as weight loss due to terminal disease. Once these factors are accounted for, the optimal body weight above age 65 corresponds to a leaner [[body mass index]] of 23 to 27.<ref name=Bowman2016>{{cite journal | vauthors = Bowman K, Delgado J, Henley WE, Masoli JA, Kos K, Brayne C, Thokala P, Lafortune L, Kuchel GA, Ble A, Melzer D | display-authors = 6 | title = Obesity in Older People With and Without Conditions Associated With Weight Loss: Follow-up of 955,000 Primary Care Patients | journal = The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences | volume = 72 | issue = 2 | pages = 203–209 | date = February 2017 | pmid = 27492450 | pmc = 5233914 | doi = 10.1093/gerona/glw147 }}</ref>
 
 
 
Alternatively, the benefits of dietary restriction can also be found by changing the [[Nutrient|macro nutrient]] profile to reduce protein intake without any changes to calorie level, resulting in similar increases in longevity.<ref>{{cite journal | vauthors = Nakagawa S, Lagisz M, Hector KL, Spencer HG | title = Comparative and meta-analytic insights into life extension via dietary restriction | journal = Aging Cell | volume = 11 | issue = 3 | pages = 401–9 | date = June 2012 | pmid = 22268691 | doi = 10.1111/j.1474-9726.2012.00798.x | s2cid = 19043668 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Simpson SJ, Raubenheimer D | title = Macronutrient balance and lifespan | journal = Aging | volume = 1 | issue = 10 | pages = 875–80 | date = October 2009 | pmid = 20157561 | pmc = 2815731 | doi = 10.18632/aging.100098 }}</ref> Dietary protein restriction not only inhibits mTOR activity but also IGF-1, two mechanisms implicated in ageing.<ref name="Fontana2010">{{cite journal | vauthors = Fontana L, Partridge L, Longo VD | title = Extending healthy life span—from yeast to humans | journal = Science | volume = 328 | issue = 5976 | pages = 321–6 | date = April 2010 | pmid = 20395504 | pmc = 3607354 | doi = 10.1126/science.1172539 | bibcode = 2010Sci...328..321F }}</ref> Specifically, reducing [[leucine]] intake is sufficient to inhibit mTOR activity, achievable through reducing animal food consumption.<ref name=":1">{{cite journal | vauthors = Melnik BC | title = Leucine signaling in the pathogenesis of type 2 diabetes and obesity | journal = World Journal of Diabetes | volume = 3 | issue = 3 | pages = 38–53 | date = March 2012 | pmid = 22442749 | pmc = 3310004 | doi = 10.4239/wjd.v3.i3.38 }}</ref><ref name=":2">{{cite journal | vauthors = Yan L, Lamb RF | title = Amino acid sensing and regulation of mTORC1 | journal = Seminars in Cell & Developmental Biology | volume = 23 | issue = 6 | pages = 621–5 | date = August 2012 | pmid = 22342805 | doi = 10.1016/j.semcdb.2012.02.001 }}</ref>
 
 
 
The [[Mediterranean diet]] is credited with lowering the risk of heart disease and early death.<ref>{{cite journal | vauthors = Rees K, Takeda A, Martin N, Ellis L, Wijesekara D, Vepa A, Das A, Hartley L, Stranges S | display-authors = 6 | title = Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease | journal = The Cochrane Database of Systematic Reviews | volume = 3 | pages = CD009825 | date = March 2019 | pmid = 30864165 | pmc = 6414510 | doi = 10.1002/14651858.CD009825.pub3 | collaboration = Cochrane Heart Group }}</ref><ref name="pmid18786971">{{cite journal | vauthors = Sofi F, Cesari F, Abbate R, Gensini GF, Casini A | title = Adherence to Mediterranean diet and health status: meta-analysis | journal = BMJ | volume = 337 | issue = sep11 2 | pages = a1344 | date = September 2008 | pmid = 18786971 | pmc = 2533524 | doi = 10.1136/bmj.a1344 }}</ref> The major contributors to mortality risk reduction appear to be a higher consumption of vegetables, fish, fruits, nuts and monounsaturated fatty acids, i.e., olive oil.<ref name="deGaetano2016">{{Cite journal|title = Mediterranean diet associated with lower risk of early death in cardiovascular disease patients. ''European Society of Cardiology''|url = https://www.sciencedaily.com/releases/2016/08/160829094040.htm|journal = ScienceDaily|date = 2016-08-29|first = Giovanni|last = de Gaetano}}</ref>
 
  
The amount of [[sleep]] has an impact on mortality. People who live the longest report sleeping for six to seven hours each night.<ref>{{cite news | vauthors = Rowland R |title=Experts challenge study linking sleep, life span |date=15 February 2002 |url=http://edition.cnn.com/2002/HEALTH/02/14/sleep.study/index.html |access-date=29 October 2013 |work=CNN}}</ref><ref>{{cite journal | vauthors = Patel SR, Ayas NT, Malhotra MR, White DP, Schernhammer ES, Speizer FE, Stampfer MJ, Hu FB | display-authors = 6 | title = A prospective study of sleep duration and mortality risk in women | journal = Sleep | volume = 27 | issue = 3 | pages = 440–4 | date = May 2004 | pmid = 15164896 | doi = 10.1093/sleep/27.3.440 | doi-access = free }}</ref> Lack of sleep (<5 hours) more than doubles the risk of death from [[cardiovascular disease]], but too much sleep (>9 hours) is associated with a doubling of the risk of death, though not primarily from cardiovascular disease.<ref>{{cite journal | vauthors = Ferrie JE, Shipley MJ, Cappuccio FP, Brunner E, Miller MA, Kumari M, Marmot MG | title = A prospective study of change in sleep duration: associations with mortality in the Whitehall II cohort | journal = Sleep | volume = 30 | issue = 12 | pages = 1659–66 | date = December 2007 | pmid = 18246975 | pmc = 2276139 | doi = 10.1093/sleep/30.12.1659 | lay-url = http://www2.warwick.ac.uk/newsandevents/pressreleases/researchers_say_lack/ | lay-source = University of Warwick }}</ref> Sleeping more than 7 to 8 hours per day has been consistently associated with increased mortality, though the cause is probably other factors such as depression and socioeconomic status, which would correlate statistically.<ref>{{cite journal | vauthors = Patel SR, Malhotra A, Gottlieb DJ, White DP, Hu FB | title = Correlates of long sleep duration | journal = Sleep | volume = 29 | issue = 7 | pages = 881–9 | date = July 2006 | pmid = 16895254 | pmc = 3500381 | doi = 10.1093/sleep/29.7.881 }}; cf. {{cite journal | vauthors = Irwin MR, Ziegler M | title = Sleep deprivation potentiates activation of cardiovascular and catecholamine responses in abstinent alcoholics | journal = Hypertension | volume = 45 | issue = 2 | pages = 252–7 | date = February 2005 | pmid = 15642774 | doi = 10.1161/01.HYP.0000153517.44295.07 | doi-access = free }}</ref> Sleep monitoring of hunter-gatherer tribes from Africa and from South America has shown similar sleep patterns across continents: their average sleeping duration is 6.4 hours (with a summer/winter difference of 1 hour), afternoon naps ([[siesta]]s) are uncommon, and [[insomnia]] is very rare (tenfold less than in industrial societies).<ref>{{cite journal | vauthors = Yetish G, Kaplan H, Gurven M, Wood B, Pontzer H, Manger PR, Wilson C, McGregor R, Siegel JM | display-authors = 6 | title = Natural sleep and its seasonal variations in three pre-industrial societies | journal = Current Biology | volume = 25 | issue = 21 | pages = 2862–2868 | date = November 2015 | pmid = 26480842 | pmc = 4720388 | doi = 10.1016/j.cub.2015.09.046 }}</ref>
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Amount of [[sleep]] is related to mortality. People who live the longest report sleeping for six to seven hours each night, while the National Sleep Foundation recommends eight hours of sleep per night for optimal health. However, this range of sleep has not been shown to be causal in increasing life span, merely correlated with longer life which may be affected by various other factors. Studies linking longer or shorter sleep patterns to increased mortality do not necessarily imply that people should change their existing, and comfortable, sleep patterns. <ref> Rhonda Rowland, [https://edition.cnn.com/2002/HEALTH/02/14/sleep.study/index.html Experts challenge study linking sleep, life span] ''CNN'', February 15, 2002. Retrieved May 31, 2022.</ref>
  
[[Physical exercise]] may increase life expectancy.<ref>{{cite journal | vauthors = Gremeaux V, Gayda M, Lepers R, Sosner P, Juneau M, Nigam A | title = Exercise and longevity | journal = Maturitas | volume = 73 | issue = 4 | pages = 312–7 | date = December 2012 | pmid = 23063021 | doi = 10.1016/j.maturitas.2012.09.012 }}</ref> People who participate in moderate to high levels of physical exercise have a lower mortality rate compared to individuals who are not physically active.<ref>{{Cite book|title=Physical Activity and Health|url=https://books.google.com/books?id=WZZPc1FmL7QC&q=+United+States.+Department+of+Health.+Physical+activity+and+health:+a+report+of+the+Surgeon+General.+diane+Publishing,+1996.&pg=PA3|journal=United States Department of Health |isbn=978-1-4289-2794-0|last1=Department of Health And Human Services|first1=United States|year=1996}}</ref> Moderate levels of exercise have been correlated with preventing ageing and improving quality of life by reducing inflammatory potential.<ref>{{cite journal | vauthors = Woods JA, Wilund KR, Martin SA, Kistler BM | title = Exercise, inflammation and aging | journal = Aging and Disease | volume = 3 | issue = 1 | pages = 130–40 | date = February 2012 | pmid = 22500274 | pmc = 3320801 }}</ref> The majority of the benefits from exercise are achieved with around 3500 [[metabolic equivalent]] (MET) minutes per week.<ref name=BMJ2016/> For example, climbing stairs 10 minutes, vacuuming 15 minutes, gardening 20 minutes, running 20 minutes, and walking or bicycling for 25 minutes on a daily basis would ''together'' achieve about 3000 MET minutes a week.<ref name=BMJ2016>{{cite journal | vauthors = Kyu HH, Bachman VF, Alexander LT, Mumford JE, Afshin A, Estep K, Veerman JL, Delwiche K, Iannarone ML, Moyer ML, Cercy K, Vos T, Murray CJ, Forouzanfar MH | display-authors = 6 | title = Physical activity and risk of breast cancer, colon cancer, diabetes, ischemic heart disease, and ischemic stroke events: systematic review and dose-response meta-analysis for the Global Burden of Disease Study 2013 | journal = BMJ | volume = 354 | pages = i3857 | date = August 2016 | pmid = 27510511 | pmc = 4979358 | doi = 10.1136/bmj.i3857 }}</ref> Other research seems to suggest a relationship between regular physical exercise and cognitive functioning in old age.<ref>{{Cite journal|last1=Kramer|first1=Arthur F.|last2=Erickson|first2=Kirk I.|date=2007-08-01|title=Capitalizing on cortical plasticity: influence of physical activity on cognition and brain function|url=http://www.sciencedirect.com/science/article/pii/S1364661307001581|journal=Trends in Cognitive Sciences|language=en|volume=11|issue=8|pages=342–348|doi=10.1016/j.tics.2007.06.009|pmid=17629545|s2cid=14669210|issn=1364-6613}}</ref>
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[[Physical exercise]] may increase life expectancy. People who participate in moderate to high levels of physical exercise have a lower mortality rate compared to individuals who are not physically active.<ref> Claude Bouchard, Steven N. Blair, and William L. Haskell (eds.), ''Physical Activity and Health'' (Human Kinetics, 2012, ISBN 0736095411).</ref> Moderate levels of exercise have been correlated with preventing aging and improving quality of life by reducing inflammatory potential.<ref>Jeffrey A. Woods, Kenneth R. Wilund, Stephen A. Martin, and Brandon M. Kistler, [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3320801/ Exercise, inflammation and aging] ''Aging and Disease'' 3(1) (February 2012): 130–140. Retrieved May 31, 2022. </ref> Regular physical exercise has also been shown to have restorative properties for cognitive and brain function in old age.<ref>Arthur F. Kramer and Kirk I. Erickson, [https://www.sciencedirect.com/science/article/abs/pii/S1364661307001581 Capitalizing on cortical plasticity: influence of physical activity on cognition and brain function] ''Trends in Cognitive Sciences'' 11(8) (August 2007):342-348. Retrieved May 31, 2022.</ref>
  
Avoidance of [[chronic stress]] (as opposed to acute stress) is associated with a slower loss of [[telomere]]s in most but not all studies,<ref name="pmid26318949">{{cite journal | vauthors = Notterman DA, Mitchell C | title = Epigenetics and Understanding the Impact of Social Determinants of Health | journal = Pediatric Clinics of North America | volume = 62 | issue = 5 | pages = 1227–40 | date = October 2015 | pmid = 26318949 | pmc = 4555996 | doi = 10.1016/j.pcl.2015.05.012 | type = Review }}</ref><ref name="Quinlan2014">{{cite journal | vauthors = Quinlan J, Tu MT, Langlois EV, Kapoor M, Ziegler D, Fahmi H, Zunzunegui MV | title = Protocol for a systematic review of the association between chronic stress during the life course and telomere length | journal = Systematic Reviews | volume = 3 | issue = 40 | pages = 40 | date = April 2014 | pmid = 24886862 | pmc = 4022427 | doi = 10.1186/2046-4053-3-40 | type = Review }}</ref> and with decreased [[cortisol]] levels. A chronically high cortisol level compromises the immune system, causes cardiac damage/[[arterosclerosis]] and is associated with facial ageing, and the latter in turn is a marker for increased morbidity and mortality.<ref name="Noordam2012">{{cite journal | vauthors = Noordam R, Gunn DA, Tomlin CC, Rozing MP, Maier AB, Slagboom PE, Westendorp RG, van Heemst D, de Craen AJ | display-authors = 6 | title = Cortisol serum levels in familial longevity and perceived age: the Leiden longevity study | journal = Psychoneuroendocrinology | volume = 37 | issue = 10 | pages = 1669–75 | date = October 2012 | pmid = 22429748 | doi = 10.1016/j.psyneuen.2012.02.013 | s2cid = 16189194 }}</ref><ref name="Lazzarino2013">{{cite journal | vauthors = Lazzarino AI, Hamer M, Gaze D, Collinson P, Steptoe A | title = The association between cortisol response to mental stress and high-sensitivity cardiac troponin T plasma concentration in healthy adults | journal = Journal of the American College of Cardiology | volume = 62 | issue = 18 | pages = 1694–1701 | date = October 2013 | pmid = 23810896 | pmc = 3807660 | doi = 10.1016/j.jacc.2013.05.070 }}</ref> A meta-analysis shows that loneliness carries a higher mortality risk than smoking.<ref name="HoltLunstad2010">{{cite journal | vauthors = Holt-Lunstad J, Smith TB, Layton JB | title = Social relationships and mortality risk: a meta-analytic review | journal = PLOS Medicine | volume = 7 | issue = 7 | pages = e1000316 | date = July 2010 | pmid = 20668659 | pmc = 2910600 | doi = 10.1371/journal.pmed.1000316 }}</ref> Stress can be countered by social connection, spirituality, and (for men more clearly than for women) married life, all of which are associated with longevity.<ref>{{cite web|url=https://bewell.stanford.edu/features/social-ties-good-health|title=Social ties are good for your health |work=stanford.edu|url-status=dead|archive-url=https://web.archive.org/web/20160911082609/http://bewell.stanford.edu/features/social-ties-good-health|archive-date=11 September 2016}}</ref><ref>{{cite book | vauthors = Koenig HG, King DE, Carson VB | date = 2012 | title = Handbook of religion and health | edition = 2nd | location = New York | publisher = Oxford University Press | pages = 476 }}</ref><ref>{{cite web|url=http://www.medicaldaily.com/married-vs-single-what-science-says-better-your-health-327878|title=Married Vs Single: What Science Says Is Better For Your Health|date=2 April 2015|work=medicaldaily.com}}</ref><ref name="Shor2012">{{cite journal | vauthors = Shor E, Roelfs DJ, Bugyi P, Schwartz JE | title = Meta-analysis of marital dissolution and mortality: reevaluating the intersection of gender and age | journal = Social Science & Medicine | volume = 75 | issue = 1 | pages = 46–59 | date = July 2012 | pmid = 22534377 | pmc = 3881174 | doi = 10.1016/j.socscimed.2012.03.010 }}</ref>
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Avoidance of [[chronic stress]] (as opposed to acute stress) is associated with a slower loss of [[telomere]]s in most but not all studies, and with decreased [[cortisol]] levels, both of which are factors in increasing morbidity and mortality.   Stress can be countered by social connection, [[spirituality]], and (for men more clearly than for women) [[married]] life, all of which are associated with longevity.<ref> Harold Koenig, Dana King, and Verna B. Carson, ''Handbook of Religion and Health'' (Oxford University Press, 2012, ISBN 0195335953). </ref><ref> Lecia Bushak, [https://www.medicaldaily.com/married-vs-single-what-science-says-better-your-health-327878 Married Vs Single: What Science Says Is Better For Your Health] ''Medical Daily'', April 2, 2015. Retrieved May 31, 2022.</ref>
  
 
===Medical intervention===
 
===Medical intervention===
The following drugs and interventions have been shown to slow or reverse the biological effects of ageing in animal models, but none has yet been proven to do so in humans.
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Theoretically, extension of maximum lifespan in humans could be achieved by reducing the rate of aging damage by periodic replacement of damaged tissues, molecular repair or rejuvenation of deteriorated cells and tissues, reversal of harmful epigenetic changes, or the enhancement of enzyme telomerase activity. Research geared towards life extension strategies in various organisms is currently under way at a number of academic and private institutions. Various drugs and interventions have been shown to slow or reverse the biological effects of aging in animal models, but none has yet been proven to do so in humans.
 
 
Evidence in both animals and humans suggests that [[resveratrol]] may be a caloric restriction mimetic.<ref name="Lam2013">{{cite journal | vauthors = Lam YY, Peterson CM, Ravussin E | title = Resveratrol vs. calorie restriction: data from rodents to humans | journal = Experimental Gerontology | volume = 48 | issue = 10 | pages = 1018–24 | date = October 2013 | pmid = 23624181 | doi = 10.1016/j.exger.2013.04.005 | s2cid = 5392374 }}</ref>
 
 
 
{{as of|2015}}, [[metformin]] was under study for its potential effect on slowing ageing in the worm [[Caenorhabditis elegans|''C.elegans'']] and the [[Acheta domesticus|cricket]].<ref name=Pry2015/> Its effect on otherwise healthy humans is unknown.<ref name=Pry2015>{{cite journal | vauthors = Pryor R, Cabreiro F | title = Repurposing metformin: an old drug with new tricks in its binding pockets | journal = The Biochemical Journal | volume = 471 | issue = 3 | pages = 307–22 | date = November 2015 | pmid = 26475449 | pmc = 4613459 | doi = 10.1042/bj20150497 }}</ref>
 
 
 
[[Sirolimus|Rapamycin]] was first shown to extend lifespan in eukaryotes in 2006 by Powers ''et al.'' who showed a dose-responsive effect of rapamycin on lifespan extension in yeast cells.<ref name="pmid16418483">{{cite journal | vauthors = Powers RW, Kaeberlein M, Caldwell SD, Kennedy BK, Fields S | title = Extension of chronological life span in yeast by decreased TOR pathway signaling | journal = Genes & Development | volume = 20 | issue = 2 | pages = 174–84 | date = January 2006 | pmid = 16418483 | pmc = 1356109 | doi = 10.1101/gad.1381406 }}</ref> In a 2009 study, the lifespans of [[mice]] fed rapamycin were increased between 28 and 38% from the beginning of treatment, or 9 to 14% in total increased maximum lifespan. Of particular note, the treatment began in mice aged 20 months, the equivalent of 60 human years.<ref name="pmid19587680">{{cite journal | vauthors = Harrison DE, Strong R, Sharp ZD, Nelson JF, Astle CM, Flurkey K, Nadon NL, Wilkinson JE, Frenkel K, Carter CS, Pahor M, Javors MA, Fernandez E, Miller RA | display-authors = 6 | title = Rapamycin fed late in life extends lifespan in genetically heterogeneous mice | journal = Nature | volume = 460 | issue = 7253 | pages = 392–5 | date = July 2009 | pmid = 19587680 | pmc = 2786175 | doi = 10.1038/nature08221 | lay-url = http://www.timesonline.co.uk/tol/life_and_style/health/article6669805.ece | lay-source = The Times | bibcode = 2009Natur.460..392H | lay-date = 8 July 2009 }}</ref> Rapamycin has subsequently been shown to extend mouse lifespan in several separate experiments,<ref name="Miller2010">{{cite journal | vauthors = Miller RA, Harrison DE, Astle CM, Baur JA, Boyd AR, de Cabo R, Fernandez E, Flurkey K, Javors MA, Nelson JF, Orihuela CJ, Pletcher S, Sharp ZD, Sinclair D, Starnes JW, Wilkinson JE, Nadon NL, Strong R | display-authors = 6 | title = Rapamycin, but not resveratrol or simvastatin, extends life span of genetically heterogeneous mice | journal = The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences | volume = 66 | issue = 2 | pages = 191–201 | date = February 2011 | pmid = 20974732 | pmc = 3021372 | doi = 10.1093/gerona/glq178 }}</ref><ref name="Ingram&Roth2011">{{cite journal | vauthors = Ingram DK, Roth GS | title = Glycolytic inhibition as a strategy for developing calorie restriction mimetics | journal = Experimental Gerontology | volume = 46 | issue = 2–3 | pages = 148–54 | date = March 2011 | pmid = 21167272 | doi = 10.1016/j.exger.2010.12.001 | type = review | s2cid = 5634847 }}</ref> and is now being tested for this purpose in nonhuman primates (the [[marmoset]] monkey).<ref name=Tardif2015>{{cite journal | vauthors = Tardif S, Ross C, Bergman P, Fernandez E, Javors M, Salmon A, Spross J, Strong R, Richardson A | display-authors = 6 | title = Testing efficacy of administration of the antiaging drug rapamycin in a nonhuman primate, the common marmoset | journal = The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences | volume = 70 | issue = 5 | pages = 577–87 | date = May 2015 | pmid = 25038772 | pmc = 4400395 | doi = 10.1093/gerona/glu101 }}</ref>
 
 
 
Cancer geneticist [[Ronald A. DePinho]] and his colleagues published research on mice where [[telomerase]] activity was first genetically removed. Then, after the mice had prematurely aged, they restored telomerase activity by reactivating the telomerase gene. As a result, the mice were rejuvenated: Shrivelled testes grew back to normal and the animals regained their fertility. Other organs, such as the spleen, liver, intestines and brain, recuperated from their degenerated state. "[The finding] offers the possibility that normal human ageing could be slowed by reawakening the enzyme in cells where it has stopped working" says Ronald DePinho. However, activating telomerase in humans could potentially encourage the growth of tumours.<ref>{{cite journal |doi=10.1038/news.2010.635 |title=Telomerase reverses ageing process |year=2010 |last1=Callaway |first1=Ewen | name-list-style = vanc |journal=Nature}}</ref>
 
 
 
<!--The Bartke2011 reference has a lot of information on specific mutations which could be discussed here.—>
 
Most known genetic interventions in ''C. elegans'' increase lifespan by 1.5 to 2.5-fold. {{as of|2009}}, the record for lifespan extension in C. ''elegans'' is a single-gene mutation which increases adult survival by tenfold.<ref name="Reis2009"/> The strong conservation of some of the mechanisms of ageing discovered in model organisms imply that they may be useful in the enhancement of human survival. However, the benefits may not be proportional; longevity gains are typically greater in ''C. elegans'' than fruit flies, and greater in fruit flies than in mammals. One explanation for this is that mammals, being much longer-lived, already have many traits which promote lifespan.<ref name="Reis2009"/>
 
  
 
== Society and culture ==
 
== Society and culture ==
 
[[File:003 p4 dd.JPG|thumb|right|350px|An elderly man]]
 
[[File:003 p4 dd.JPG|thumb|right|350px|An elderly man]]
 
Different cultures express age in different ways. Most legal systems define a specific age for when an individual is allowed or obliged to do particular activities. These age specifications include [[voting age]], [[Legal drinking age|drinking age]], [[age of consent]], [[age of majority]], [[age of criminal responsibility]], [[marriageable age]], [[age of candidacy]], and [[mandatory retirement age]]. In other words, [[Chronology|chronological]] aging may be distinguished from "social aging" (cultural age-expectations of how people should act as they grow older) and "biological aging" (an organism's physical state as it ages).<ref>Judith Phillips, Kristine Ajrouch, and Sarah Hillcoat-Nallétamby, ''Key Concepts in Social Gerontology'' (SAGE Publications, 2010, ISBN 1412922720). </ref>
 
Different cultures express age in different ways. Most legal systems define a specific age for when an individual is allowed or obliged to do particular activities. These age specifications include [[voting age]], [[Legal drinking age|drinking age]], [[age of consent]], [[age of majority]], [[age of criminal responsibility]], [[marriageable age]], [[age of candidacy]], and [[mandatory retirement age]]. In other words, [[Chronology|chronological]] aging may be distinguished from "social aging" (cultural age-expectations of how people should act as they grow older) and "biological aging" (an organism's physical state as it ages).<ref>Judith Phillips, Kristine Ajrouch, and Sarah Hillcoat-Nallétamby, ''Key Concepts in Social Gerontology'' (SAGE Publications, 2010, ISBN 1412922720). </ref>
 
  
 
===Sociology===
 
===Sociology===
[[File:Menneske Aldrene (C. W. Eckersberg).png|thumb|400px|[[Christoffer Wilhelm Eckersberg]]: ''Ages of Man'']]  
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[[File:Menneske Aldrene (C. W. Eckersberg).png|thumb|350px|[[Christoffer Wilhelm Eckersberg]]: ''Ages of Man'']]  
In the field of sociology and mental health, ageing is seen in five different views: ageing as [[Maturity (psychological)|maturity]], ageing as decline, ageing as a life-cycle event, ageing as generation, and ageing as survival.<ref>{{cite book| vauthors = Scheid TL, Brown TN |title=A Handbook for the Study of Mental Health|date=2010|publisher=Cambridge University Press|location=New York|edition=Second}}</ref> Positive correlates with ageing often include economics, employment, marriage, children, education, and sense of control, as well as many others. The [[social science of aging|social science of ageing]] includes disengagement theory, activity theory, selectivity theory, and continuity theory. [[Retirement]], a common transition faced by the elderly, may have both positive and negative consequences.<ref>{{cite book| vauthors = Panek PE, Hayslip B |title=Adult development and aging|publisher=Harper & Row|location=San Francisco|year=1989|isbn=978-0-06-045012-0}}{{page needed|date=November 2013}}</ref> As cyborgs currently are on the rise some theorists argue there is a need to develop new definitions of ageing and for instance a bio-techno-social definition of ageing has been suggested.<ref name="pmid25456627">{{cite journal | vauthors = Wejbrandt A | title = Defining aging in cyborgs: a bio-techno-social definition of aging | journal = Journal of Aging Studies | volume = 31 | pages = 104–9 | date = December 2014 | pmid = 25456627 | doi = 10.1016/j.jaging.2014.09.003 }}</ref>
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In the fielda of [[sociology]] and [[mental health]], ageing is seen in five different views: aging as [[Maturity (psychological)|maturity]], aging as decline, aging as a life-cycle event, aging as generation, and aging as survival.<ref>Teresa L. Scheid and Eric R. Wright (eds.), ''A Handbook for the Study of Mental Health'' (Cambridge University Press, 2017, ISBN 9781316500965).</ref> Positive correlates with aging often include economics, employment, marriage, children, education, and sense of control. [[Retirement]], a common transition faced by the elderly, may have both positive and negative consequences.<ref>Susan K. Whitbourne and Stacey B. Whitbourne, ''Adult Development and Aging'' (Wiley, 2020, ISBN 1119667453).</ref>  
  
There is a current debate as to whether or not the pursuit of [[longevity]] and the postponement of senescence are cost-effective health care goals given finite health care resources. Because of the accumulated infirmities of old age, bioethicist [[Ezekiel Emanuel]], opines that the pursuit of longevity via the [[compression of morbidity]] hypothesis is a "fantasy" and that human life is not worth living after age 75; longevity then should not be a goal of health care policy.<ref name=Emmanuel>{{Cite journal|last1=Emmanuel EJ|title=Why I hope to die at 75: An argument that society and families – and you – will be better off if nature takes its course swiftly and promptly|journal=The Atlantic|url=https://www.theatlantic.com/features/archive/2014/09/why-i-hope-to-die-at-75/379329/|access-date=7 April 2015|date=October 2014 }}</ref> This opinion has been contested by neurosurgeon and medical ethicist [[Miguel Faria]], who states that life can be worthwhile during old age, and that longevity should be pursued in association with the attainment of quality of life.<ref name="Faria 75">{{cite journal | vauthors = Faria MA | title = Bioethics and why I hope to live beyond age 75 attaining wisdom!: A rebuttal to Dr. Ezekiel Emanuel's 75 age limit | journal = Surgical Neurology International | year = 2015 | volume = 6 | pages = 35 | pmid = 25789197 | doi = 10.4103/2152-7806.152733 | pmc = 4360549 }}</ref> Faria claims that postponement of senescence as well as happiness and wisdom can be attained in old age in a large proportion of those who lead healthy lifestyles and remain intellectually active.<ref name="Faria longevity">{{cite journal | vauthors = Faria MA | title = Longevity and compression of morbidity from a neuroscience perspective: Do we have a duty to die by a certain age? | journal = Surgical Neurology International | volume = 6 | pages = 49 | date = 2015 | pmid = 25883841 | pmc = 4392568 | doi = 10.4103/2152-7806.154273 }}</ref>
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Population aging is the increase in the number and proportion of older people in society. Population aging occurs through [[human migration|migration]], longer [[life expectancy]] (decreased death rate), and decreased birth rate. As a population ages, it has a significant impact on society. Young people tend to have fewer legal privileges (if they are below the [[age of majority]]), they are more likely to push for political and social change, to develop and adopt new technologies, and to need education. Older people have different requirements from society and government, and frequently have differing values as well, such as for property and pension rights.<ref>John A. Vincent, [https://pubmed.ncbi.nlm.nih.gov/16309437/ Understanding generations: political economy and culture in an ageing society] ''The British Journal of Sociology'' 56(4) (December 2005): 579–599. Retrieved May 31, 2022.</ref>
  
 
=== Economics ===
 
=== Economics ===
Population ageing is the increase in the number and proportion of older people in society. Population ageing has three possible causes: migration, longer [[life expectancy]] (decreased death rate) and decreased birth rate. Ageing has a significant impact on society. Young people tend to have fewer legal privileges (if they are below the [[age of majority]]), they are more likely to push for political and social change, to develop and adopt new technologies, and to need education. Older people have different requirements from society and government, and frequently have differing values as well, such as for property and pension rights.<ref name="Vincent 2005">{{cite journal | vauthors = Vincent JA | title = Understanding generations: political economy and culture in an ageing society | journal = The British Journal of Sociology | volume = 56 | issue = 4 | pages = 579–99 | date = December 2005 | pmid = 16309437 | doi = 10.1111/j.1468-4446.2005.00084.x | s2cid = 1775770 }}</ref>
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Among the most urgent concerns of older persons worldwide is income security. This poses challenges for governments with aging populations to ensure that investment in pension systems is sufficient to provide economic independence and reduce poverty in old age. These challenges vary for developing and developed countries:
 
+
<blockquote>Sustainability of these systems is of particular concern, particularly in developed countries, while social protection and old-age pension coverage remain a challenge for developing countries, where a large proportion of the labour force is found in the informal sector.<ref name=UNPF> Jose Miguel Guzman, Ann Pawliczko, Sylvia Beales, Celia Till, and Ina Voelcker (ed.), ''Ageing in the Twenty-First Century: A Celebration and a Challenge'' (United Nations Population Fund, HelpAge International, 2012, ISBN 0897149815).</ref></blockquote>
In the 21st century, one of the most significant population trends is ageing.<ref>{{cite web |url=http://www.unfpa.org/publications/population-ageing-and-development-0 |title=Population Ageing and Development |year=2002 |publisher= UNFPA}}</ref> Currently, over 11% of the world's current population are people aged 60 and older and the [[United Nations Population Fund]] (UNFPA) estimates that by 2050 that number will rise to approximately 22%.<ref name="Ageing in the Twenty-First Century">{{cite web |url=http://www.unfpa.org/publications/ageing-twenty-first-century |title=Ageing in the Twenty-First Century |year=2012 |publisher= UNFPA}}</ref> Ageing has occurred due to development which has enabled better nutrition, sanitation, health care, education and economic well-being. Consequently, fertility rates have continued to decline and life expectancy has risen. Life expectancy at birth is over 80 now in 33 countries. Ageing is a "global phenomenon", that is occurring fastest in developing countries, including those with large youth populations, and poses social and economic challenges to the work which can be overcome with "the right set of policies to equip individuals, families and societies to address these challenges and to reap its benefits".<ref name="unfpa.org">{{cite web|url=http://www.unfpa.org/ageing|title=Ageing |publisher= UNFPA – United Nations Population Fund|work=unfpa.org}}</ref>
 
 
 
As life expectancy rises and [[birth rates]] decline in developed countries, the [[median]] age rises accordingly. According to the [[United Nations]], this process is taking place in nearly every country in the world.<ref name="devrep05">{{Cite web|url=http://hdr.undp.org/en/media/HDR05_complete.pdf
 
|title=UN Human Development Report 2005|access-date=7 October 2010|publisher=United Nations Development Programme |archive-url = https://web.archive.org/web/20080527203423/http://hdr.undp.org/en/media/hdr05_complete.pdf |archive-date = 27 May 2008}}</ref> A rising median age can have significant social and economic implications, as the workforce gets progressively older and the number of old workers and retirees grows relative to the number of young workers. Older people generally incur more health-related costs than do younger people in the workplace and can also cost more in worker's compensation and pension liabilities.<ref name="aging-workforce">{{cite web|last=Chosewood|first=L. Casey|title=Safer and Healthier at Any Age: Strategies for an Aging Workforce|url=http://blogs.cdc.gov/niosh-science-blog/2012/07/agingworkforce/|work=NIOSH Science Blog|publisher=National Institute for Occupational Safety and Health|access-date=6 August 2012}}</ref> In most developed countries an older workforce is somewhat inevitable. In the United States for instance, the [[Bureau of Labor Statistics]] estimates that one in four American workers will be 55 or older by 2020.<ref name = aging-workforce/>
 
 
 
Among the most urgent concerns of older persons worldwide is income security. This poses challenges for governments with ageing populations to ensure investments in pension systems continues in order to provide economic independence and reduce poverty in old age. These challenges vary for developing and developed countries. UNFPA stated that, "Sustainability of these systems is of particular concern, particularly in developed countries, while social protection and old-age pension coverage remain a challenge for developing countries, where a large proportion of the labour force is found in the informal sector."<ref name="Ageing in the Twenty-First Century"/>
 
 
 
The global economic crisis has increased financial pressure to ensure economic security and access to health care in old age. In order to elevate this pressure "social protection floors must be implemented in order to guarantee income security and access to essential health and social services for all older persons and provide a safety net that contributes to the postponement of disability and prevention of impoverishment in old age".<ref name="Ageing in the Twenty-First Century"/>
 
 
 
It has been argued that population ageing has undermined economic development.<ref name="Basakha 2015">{{cite journal| vauthors = Basakha M, Yavari K, Sadeghi H, Naseri A |title=Population Aging And Iran's Non-Oil Economic Growth|journal= Payavard Salamat |year=2015|volume= 9 |issue=2|pages= 131–46|url=http://payavard.tums.ac.ir/browse.php?a_code=A-10-1-113&sid=1&slc_lang=en}}</ref> Evidence suggests that pensions, while making a difference to the well-being of older persons, also benefit entire families especially in times of crisis when there may be a shortage or loss of employment within households. A study by the Australian Government in 2003 estimated that "women between the ages of 65 and 74 years contribute A$16 billion per year in unpaid caregiving and voluntary work. Similarly, men in the same age group contributed A$10 billion per year."<ref name="Ageing in the Twenty-First Century"/>
 
 
 
Due to increasing share of the elderly in the population, health care expenditures will continue to grow relative to the economy in coming decades. This has been considered as a negative phenomenon and effective strategies like labour productivity enhancement should be considered to deal with negative consequences of ageing.<ref name="Basakha 2014">{{cite journal | vauthors = Basakha M, Yavari K, Sadeghi H, Naseri A | title = Health care cost disease as a threat to Iranian aging society | journal = Journal of Research in Health Sciences | volume = 14 | issue = 2 | pages = 152–6 | year = 2014 | pmid = 24728752 | url = http://jrhs.umsha.ac.ir/index.php/JRHS/article/view/1109/pdf }}</ref>
 
 
 
 
 
=== Health care demand ===
 
 
 
With age inevitable biological changes occur that increase the risk of illness and disability. UNFPA states that,<ref name="unfpa.org"/>
 
  
"A life-cycle approach to health care – one that starts early, continues through the reproductive years and lasts into old age – is essential for the physical and emotional well-being of older persons, and, indeed, all people. Public policies and programmes should additionally address the needs of older impoverished people who cannot afford health care."
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=== Health care ===
 +
With age inevitable biological changes occur that increase the risk of illness and disability. A number of health problems become more prevalent as people get older. These include [[mental health]] problems as well as physical health problems, especially [[dementia]].  
  
Many societies in Western Europe and Japan have ageing populations. While the effects on society are complex, there is a concern about the impact on health care demand. The large number of suggestions in the literature for specific interventions to cope with the expected increase in demand for long-term care in ageing societies can be organised under four headings: improve system performance; redesign service delivery; support informal caregivers; and shift demographic parameters.<ref name=Saltman2006>{{cite journal | vauthors = Saltman RB, Dubois HF, Chawla M | title = The impact of aging on long-term care in Europe and some potential policy responses | journal = International Journal of Health Services | volume = 36 | issue = 4 | pages = 719–46 | year = 2006 | pmid = 17175843 | doi = 10.2190/AUL1-4LAM-4VNB-3YH0 | s2cid = 45396303 }}</ref>
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While the effects on society of population aging are multidimensional, there is no doubt about its impact on health care demand:
 
+
<blockquote>A life-cycle approach to health care – one that starts early, continues through the reproductive years and lasts into old age – is essential for the physical and emotional well-being of older persons, and, indeed, all people. Public policies and programmes should additionally address the needs of older impoverished people who cannot afford health care.<ref name=UNPF/></blockquote>
However, the annual growth in national health spending is not mainly due to increasing demand from ageing populations, but rather has been driven by rising incomes, costly new medical technology, a shortage of health care workers and informational asymmetries between providers and patients.<ref name=Rheinhardt2003>{{cite journal | vauthors = Reinhardt UE | title = Does the aging of the population really drive the demand for health care? | journal = Health Affairs | volume = 22 | issue = 6 | pages = 27–39 | year = 2003 | pmid = 14649430 | doi = 10.1377/hlthaff.22.6.27 | doi-access = free }}</ref> A number of health problems become more prevalent as people get older. These include mental health problems as well as physical health problems, especially [[dementia]].
 
 
 
It has been estimated that population ageing only explains 0.2 percentage points of the annual growth rate in medical spending of 4.3% since 1970. In addition, certain reforms to the Medicare system in the United States decreased elderly spending on home health care by 12.5% per year between 1996 and 2000.<ref name="Meara2004.">{{cite journal | vauthors = Meara E, White C, Cutler DM | title = Trends in medical spending by age, 1963-2000 | journal = Health Affairs | volume = 23 | issue = 4 | pages = 176–83 | year = 2004 | pmid = 15318578 | doi = 10.1377/hlthaff.23.4.176 | doi-access = free }}</ref>
 
  
 
===Self-perception===
 
===Self-perception===
As humans age, their bodies begin to break down and their skin begins to look different, but people do not always welcome these changes to their appearance.<ref>{{Cite web|date=2014-02-20|title=Here's Everything That's Wrong With Our 'Under 30' Obsession|url=https://www.huffpost.com/entry/why-30-under-30-lists-mis_n_4791178|access-date=2021-03-12|website=HuffPost|language=en}}</ref>
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As humans age, their bodies begin to break down, and among other changes their skin begins to look different. However, especially in Western culture, these changes are not always appreciated and being young, or at least youthful, is celebrated especially when young people are successful.<ref>Carolyn Gregoire, [https://www.huffpost.com/entry/why-30-under-30-lists-mis_n_4791178 Here's Everything That's Wrong With Our 'Under 30' Obsession] ''Huffington Post'', February 25, 2014. Retrieved May 31, 2022.</ref>
 
 
[[Beauty standards]] have evolved over time, and as scientific research in cosmeceuticals has increased, the industry has also expanded; the kinds of products they produce (such as serums and creams) have gradually gained popularity and become a part of many people's personal care routine.<ref>{{cite journal | vauthors = Kattimani V, Tiwari RV, Gufran K, Wasan B, Shilpa PH, Khader AA | title = Botulinum Toxin Application in Facial Esthetics and Recent Treatment Indications (2013-2018) | journal = Journal of International Society of Preventive & Community Dentistry | volume = 9 | issue = 2 | pages = 99–105 | date = March 2019 | pmid = 31058058 | pmc = 6489509 | doi = 10.4103/jispcd.JISPCD_430_18 | quote = Standards of beauty have changed through centuries with increased awareness about esthetics. }}</ref> The cosmeceutical industry is currently the fastest growing beauty industry, with a market size of $49.5 billion for the year 2018.<ref>{{Cite web|title=Global Cosmeceutical Market Size & Share Report, 2019-2025|url=https://www.grandviewresearch.com/industry-analysis/cosmeceutical-market|access-date=2021-03-12|website=www.grandviewresearch.com|language=en}}</ref>
 
 
 
The increase in demand for cosmeceuticals has led scientists to find ingredients for these products in unorthodox places. For example, cryptomphalus aspersa secretion (or brown garden snail secretion) has been found to have antioxidant properties, increase skin cell proliferation, as well as increase extracellular proteins such as collagen and fibronectin (important proteins for cell proliferation).<ref>{{cite journal | vauthors = Juhász ML, Levin MK, Marmur ES | title = The use of natural ingredients in innovative Korean cosmeceuticals | journal = Journal of Cosmetic Dermatology | volume = 17 | issue = 3 | pages = 305–312 | date = June 2018 | pmid = 29363245 | doi = 10.1111/jocd.12492 | s2cid = 25982162 }} {{verify source |date=August 2019 |reason=This ref was deleted ([[Special:Diff/909069547]]) by a bug in VisualEditor and later restored by a bot from the original cite at [[Special:Permalink/909069468]] cite #3 - please verify the cite's accuracy and remove this {verify source} template. [[User:GreenC bot/Job 18]]}}</ref> Another substance used to prevent the physical manifestations of aging is onobotulinumtoxinA, the toxin injected for Botox.<ref>{{Cite web|title=Botox injections - Mayo Clinic|url=https://www.mayoclinic.org/tests-procedures/botox/about/pac-20384658#:~:text=Botox%20injections%20are%20relatively%20safe,Headache%20or%20flu-like%20symptoms|access-date=2021-03-12|website=www.mayoclinic.org}}</ref>
 
 
 
Generally, aversion to ageing is a Western attitude. However, in other places around the world, old age is celebrated and honored. In Korea, for example, a special party called [[hwangap]] is held to celebrate and congratulate an individual for turning 60 years old.<ref>{{Cite web|title=Korea - Birthday Celebrations|url=http://www.asianinfo.org/asianinfo/korea/cel/birthday_celebrations.htm|access-date=2021-03-12|website=www.asianinfo.org}}</ref>
 
  
Positive self-perceptions of aging are associated with better mental and physical health and well-being.<ref name="Sabatini2019">{{cite journal | vauthors = Sabatini S, Silarova B, Martyr A, Collins R, Ballard C, Anstey KJ, Kim S, Clare L | display-authors = 6 | title = Associations of Awareness of Age-Related Change With Emotional and Physical Well-being: A Systematic Review and Meta-analysis | journal = The Gerontologist | volume = 60 | issue = 6 | pages = e477–e490 | date = August 2020 | pmid = 31350849 | pmc = 7427487 | doi = 10.1093/geront/gnz101 | doi-access = free }}</ref> Positive [[Self-rated health|self-perception of health]] has been correlated with higher well-being and reduced mortality among the elderly.<ref name=Idler2003>{{cite journal |doi=10.1093/geront/43.3.372 |title=Discussion: Gender Differences in Self-Rated Health, in Mortality, and in the Relationship Between the Two |year=2003 | vauthors = Idler EL |journal=The Gerontologist |volume=43 |issue=3 |pages=372–75|doi-access=free }}</ref><ref name=Deeg2003>{{cite journal | vauthors = Deeg DJ, Bath PA | title = Self-rated health, gender, and mortality in older persons: introduction to a special section | journal = The Gerontologist | volume = 43 | issue = 3 | pages = 369–71 | date = June 2003 | pmid = 12810900 | doi = 10.1093/geront/43.3.369 | doi-access = free }}</ref> Various reasons have been proposed for this association; people who are objectively healthy may naturally rate their health better as than that of their ill counterparts, though this link has been observed even in studies which have controlled for [[socioeconomic status]], psychological functioning and health status.<ref name=Benyamini2003>{{cite journal | vauthors = Benyamini Y, Blumstein T, Lusky A, Modan B | title = Gender differences in the self-rated health-mortality association: is it poor self-rated health that predicts mortality or excellent self-rated health that predicts survival? | journal = The Gerontologist | volume = 43 | issue = 3 | pages = 396–405; discussion 372–5 | date = June 2003 | pmid = 12810904 | doi = 10.1093/geront/43.3.396 | doi-access = free }}</ref> This finding is generally stronger for men than women,<ref name=Deeg2003/> though this relationship is not universal across all studies and may only be true in some circumstances.<ref name=Benyamini2003/>
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Generally, aversion to aging and its effects is primarily a Western attitude. In other places around the world, old age is celebrated and honored. In Korea, for example, a special party called ''[[hwangap]]'' is held to celebrate and congratulate an individual for turning 60 years old.<ref>[http://www.asianinfo.org/asianinfo/korea/cel/birthday_celebrations.htm Korea - Birthday Celebrations] ''Asian Info''. Retrieved May 31, 2022.</ref>
  
As people age, subjective health remains relatively stable, even though objective health worsens.<ref name=Kunz2000>{{cite journal | vauthors = Kunzmann U, Little TD, Smith J | title = Is age-related stability of subjective well-being a paradox? Cross-sectional and longitudinal evidence from the Berlin Aging Study | journal = Psychology and Aging | volume = 15 | issue = 3 | pages = 511–26 | date = September 2000 | pmid = 11014714 | doi = 10.1037/0882-7974.15.3.511 }}</ref> In fact, perceived health improves with age when objective health is controlled in the equation.<ref>{{cite journal | vauthors = Jylhä M, Guralnik JM, Balfour J, Fried LP | title = Walking difficulty, walking speed, and age as predictors of self-rated health: the women's health and aging study | journal = The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences | volume = 56 | issue = 10 | pages = M609-17 | date = October 2001 | pmid = 11584033 | doi = 10.1093/gerona/56.10.m609 | doi-access = free }}</ref> This phenomenon is known as the "paradox of ageing". This may be a result of [[social comparison]];<ref>{{cite book|last1=Heckhausen|first1=Jutta | name-list-style = vanc |title=Developmental Regulation in Adulthood: Age-Normative and Sociostructural Constraints as Adaptive Challenges|url=https://archive.org/details/developmentalreg0000heck|url-access=registration|isbn=978-0-521-02713-7|date=1999|publisher=Cambridge University Press}}</ref> for instance, the older people get, the more they may consider themselves in better health than their same-aged peers.<ref>{{cite journal | vauthors = Sargent-Cox KA, Anstey KJ, Luszcz MA | title = Determinants of self-rated health items with different points of reference: implications for health measurement of older adults | journal = Journal of Aging and Health | volume = 20 | issue = 6 | pages = 739–61 | date = September 2008 | pmid = 18625760 | doi = 10.1177/0898264308321035 | s2cid = 34866893 }}</ref> Elderly people often associate their functional and physical decline with the normal ageing process.<ref>{{cite journal | vauthors = Idler EL | title = Age differences in self-assessments of health: age changes, cohort differences, or survivorship? | journal = Journal of Gerontology | volume = 48 | issue = 6 | pages = S289-300 | date = November 1993 | pmid = 8228003 | doi = 10.1093/geronj/48.6.s289 }}</ref><ref>{{cite journal | vauthors = Williamson JD, Fried LP | title = Characterization of older adults who attribute functional decrements to "old age" | journal = Journal of the American Geriatrics Society | volume = 44 | issue = 12 | pages = 1429–34 | date = December 1996 | pmid = 8951311 | doi = 10.1111/j.1532-5415.1996.tb04066.x | s2cid = 21027678 }}</ref>
+
Positive self-perceptions of aging are associated with better mental and physical health and well-being.<ref>Serena Sabatini, Barbora Silarova, Anthony Martyr, Rachel Collins, Clive Ballard, Kaarin J. Anstey, Sarang Kim, and Linda Clare, [https://pubmed.ncbi.nlm.nih.gov/31350849/ Associations of Awareness of Age-Related Change With Emotional and Physical Well-being: A Systematic Review and Meta-analysis] ''The Gerontologist'' 60(6) (August 2020): e477–e490. Retrieved May 31, 2022.</ref> Positive self-perception of [[health]] has been correlated with higher well-being and reduced mortality among the elderly. Various reasons have been proposed for this association; people who are objectively healthy may naturally rate their health better as than that of their ill counterparts.
  
One way to help younger people experience what it feels like to be older is through an [[ageing suit]]. There are several different kinds of suits including the GERT (named as a reference to [[gerontology]]), the R70i exoskeleton, and the AGNES (Age Gain Now Empathy Suit) suits.<ref name=":0">{{Cite web|title=40 Years In 5 Minutes: Age Simulation Suit Aims To Increase Empathy In Building Design|url=https://www.wbur.org/hereandnow/2019/06/03/age-simulation-suit|access-date=2021-03-12|website=www.wbur.org|language=en}}</ref><ref>{{Cite web|last=Prindle|first=Drew|date=7 January 2016|title=Hands on: Genworth R70i Exoskeleton|url=https://www.digitaltrends.com/cool-tech/genworth-r70i-exoskeleton/|url-status=live|access-date=12 March 2021|website=digitaltrends}}</ref><ref name=":3">{{Cite web|title=AGNES (Age Gain Now Empathy System) {{!}} MIT AgeLab|url=https://agelab.mit.edu/agnes-age-gain-now-empathy-system#:~:text=AGNES%20is%20a%20suit%20worn,physical%20challenges%20associated%20with%20aging|access-date=2021-03-12|website=agelab.mit.edu}}</ref> These suits create the feelings of the effects of aging by adding extra weight and increased pressure in certain points like the wrists, ankles and other joints. In addition, the various suits have different ways to impair vision and hearing to simulate the loss of these senses. To create the loss of feeling in hands that the elderly experience, special gloves are a part of the uniforms.
+
As people age, subjective health remains relatively stable, even though objective health worsens. In fact, perceived health improves with age when objective health is controlled in the equation. This phenomenon is known as the "paradox of aging," and may be a result of [[social comparison]]; for instance, the older people get, the more they may consider themselves in better health than their same-aged peers. Elderly people often associate their functional and physical decline with the normal aging process.<ref>Jutta Heckhausen, ''Developmental Regulation in Adulthood: Age-Normative and Sociostructural Constraints as Adaptive Challenges'' (Cambridge University Press, 2006, ISBN 0521027136). </ref>
  
Use of these suits may help to increase the amount of empathy felt for the elderly and could be considered particularly useful for those who are either learning about aging, or those who work with the elderly, such as nurses or care center staff.
+
===Successful aging===
 
+
Traditional definitions of successful aging have emphasized absence of physical and cognitive disabilities.<ref>Paul B. Baltes and Margaret M. Baltes, ''Successful Aging'' (Cambridge University Press, 1993, ISBN 052143582X). </ref> Successful aging has been characterized as involving three components: a) freedom from disease and disability, b) high cognitive and physical functioning, and c) social and productive engagement.<ref>J.W. Rowe and R.L. Kahn, [https://pubmed.ncbi.nlm.nih.gov/3299702/ Human aging: usual and successful] ''Science'' 237(4811) (July 1987): 143–149. Retrieved May 31, 2022.</ref>
Empathy is another field that could benefit from the empathy these suits may cause.<ref name=":0" /><ref name=":3" /> When designers understand what it feels like to have the impairments of old age, they can better design buildings, packaging, or even tools to help with the simple day-to-day tasks that are more difficult with less dexterity. Designing with the elderly in mind may help to reduce the negative feelings that are associated with the loss of abilities that the elderly face.
 
 
 
===Successful ageing===
 
The concept of ''successful ageing'' can be traced back to the 1950s and was popularised in the 1980s. Traditional definitions of successful ageing have emphasised absence of physical and cognitive disabilities.<ref>{{cite book |doi=10.1017/CBO9780511665684.003 |chapter=Psychological perspectives on successful aging: The model of selective optimization with compensation |title=Successful Aging |year=1990 | vauthors = Baltes PB, Baltes MM | veditors = Baltes PB, Baltes MM |isbn=978-0-511-66568-4 |pages=1–34}}</ref> In their 1987 article, Rowe and Kahn characterised successful ageing as involving three components: a) freedom from disease and disability, b) high cognitive and physical functioning, and c) social and productive engagement.<ref name="Human aging: Usual and successful">{{cite journal | vauthors = Rowe JW, Kahn RL | title = Human aging: usual and successful | journal = Science | volume = 237 | issue = 4811 | pages = 143–9 | date = July 1987 | pmid = 3299702 | doi = 10.1126/science.3299702 | bibcode = 1987Sci...237..143R }}</ref>
 
  
 
== Notes ==
 
== Notes ==
Line 201: Line 134:
  
 
==References==
 
==References==
 +
*Baltes, Paul B., and Margaret M. Baltes. ''Successful Aging''. Cambridge University Press, 1993. ISBN 052143582X
 +
*Bouchard, Claude, Steven N. Blair, and William L. Haskell (eds.). ''Physical Activity and Health''. Human Kinetics, 2012. ISBN 0736095411
 +
*Guzman, Jose Miguel, Ann Pawliczko, Sylvia Beales, Celia Till, and Ina Voelcker (eds.). ''Ageing in the Twenty-First Century: A Celebration and a Challenge''. United Nations Population Fund, HelpAge International, 2012. ISBN 0897149815
 +
*Heckhausen, Jutta. ''Developmental Regulation in Adulthood: Age-Normative and Sociostructural Constraints as Adaptive Challenges''. Cambridge University Press, 2006. ISBN 0521027136
 +
*Koenig, Harold, Dana King, and Verna B. Carson. ''Handbook of Religion and Health''. Oxford University Press, 2012. ISBN 0195335953
 +
*Lazaro, Rolando T., Sandra G. Reina-Guerra, and Myla Quiben. ''Umphred's Neurological Rehabilitation''. Mosby, 2019. ISBN 0323611176
 +
*Masoro, Edward J., and Steven N. Austad (eds.). ''Handbook of the Biology of Aging''. Academic Press, 2006. ISBN  0120883872
 
*McDonald, Roger B. ''Biology of Aging''. Garland Science, 2019. ISBN 0815345674
 
*McDonald, Roger B. ''Biology of Aging''. Garland Science, 2019. ISBN 0815345674
 +
*Phillips, Judith, Kristine Ajrouch, and Sarah Hillcoat-Nallétamby. ''Key Concepts in Social Gerontology''. SAGE Publications, 2010. ISBN 1412922720
 +
*Schaie, K. Warner. ''Developmental Influences on Adult Intelligence''. Oxford University Press, 2012. ISBN 0195386132
 +
*Scheid, Teresa L., and Eric R. Wright (eds.). ''A Handbook for the Study of Mental Health''. Cambridge University Press, 2017. ISBN 9781316500965
 +
*Stuart-Hamilton, Ian. ''The Psychology of Ageing: An Introduction''. Jessica Kingsley Publishers, 2012. ISBN 184905245X
 +
*Whitbourne, Susan K., and Stacey B. Whitbourne. ''Adult Development and Aging''. Wiley, 2020. ISBN 1119667453
  
 
== External links ==
 
== External links ==
All links retrieved  
+
All links retrieved June 16, 2023.
 
* [https://sites.pitt.edu/~dash/aging.html Aging and Death in Folklore]
 
* [https://sites.pitt.edu/~dash/aging.html Aging and Death in Folklore]
 
* [https://www.helpage.org/global-agewatch/ Global AgeWatch]  
 
* [https://www.helpage.org/global-agewatch/ Global AgeWatch]  
 
* [https://www.helpage.org/resources/ageing-in-the-21st-century-a-celebration-and-a-challenge/ Ageing in the 21st Century] ''HelpAge International''
 
* [https://www.helpage.org/resources/ageing-in-the-21st-century-a-celebration-and-a-challenge/ Ageing in the 21st Century] ''HelpAge International''
 
+
* [https://www.nia.nih.gov/ National Institute on Aging]
 
+
* [https://www.mayoclinic.org/healthy-lifestyle/healthy-aging/in-depth/aging/art-20046070 Healthy aging] ''Mayo Clinic''
  
 
[[Category:Life sciences]]
 
[[Category:Life sciences]]
 
[[Category:Social sciences]]
 
[[Category:Social sciences]]
 
{{Credits|Ageing|1023559864}}
 
{{Credits|Ageing|1023559864}}

Latest revision as of 06:45, 16 June 2023


95-year-old woman holding a five-month-old boy

Aging or ageing is the process of becoming older. The term refers especially to humans, many other animals, and fungi. In the broader sense, aging can refer to single cells within an organism which have ceased dividing (cellular senescence) or to the population of a species (population aging).

This article focuses primarily on humans. Aging represents the accumulation of changes in a human being over time and can encompass physical, psychological, and social changes. Reaction time, for example, may slow with age, while memories and general knowledge typically increase. Society's view of aging, for example valuing youth over experience, affects a person's self-perception of their own aging. A belief in an afterlife, the continued existence of an eternal spirit or soul after the death of the physical body, gives a different view to aging and reduces the stress associated with physical deterioration.

Definitions

Biological aging refers to an organism's increased rate of death as it progresses through its lifecycle and increases its chronological age.[1] Another possible way to define aging is through functional definitions, of which there are two main types: The first describes how varying types of deteriorative changes that accumulate in the life of a post-maturation organism can leave it vulnerable, leading to a decreased ability of the organism to survive: "Aging is the progressive accumulation of changes with time that are associated with or responsible for the ever-increasing susceptibility to disease and death which accompanies advancing age."[2] The second is a senescence-based definition which describes age-related changes in an organism that increase its mortality rate over time by negatively affecting its vitality and functional performance.[1]

Did you know?
Aging is the natural biological process that all animal life, including human beings, go through from conception to death

An important distinction to make is that biological aging is not the same as the accumulation of diseases related to old age; disease is a blanket term used to describe a process within an organism that causes a decrease in its functional ability.[1] Aging is the natural and inevitable biological process that all animal life, including human beings, go through from conception through birth to death. While death by other external causes, such as disease, accident, predation, and so forth, is common, nonetheless death would occur naturally due to aging even in the absence of such causes.

Biological basis

The causes of aging are uncertain, but appear to involve a number of factors.[3] The factors proposed to influence biological aging fall into two main categories: programmed and damage-related. They are not necessarily mutually exclusive.

The first posits that aging is programmed and therefore follows an inexorable path, a biological timetable, perhaps one that might be a continuation of that which regulates childhood growth and development. This regulation would depend on changes in gene expression that affect the systems responsible for maintenance, repair, and defense responses. Programmed aging should not be confused with programmed cell death (apoptosis).

The second category of theories suggests various sources and targets of damage that lead to aging. Damage-related factors include internal and environmental assaults to living organisms that induce cumulative damage at various levels.

A third, novel concept is that aging is mediated by vicious cycles.[4]

Additionally, there can be other reasons which can speed up the rate of aging in organisms including human beings, such as obesity and compromised immune system.

Programmed factors

The programmed approach suggests three major mechanisms which control aging:[5]

Programmed Longevity

Aging is the result of a sequential switching on and off of certain genes, with senescence being defined as the time when age-associated deficits are manifested.

Endocrine Theory

Biological clocks act through hormones to control the pace of aging.

Immunological Theory

The immune system is programmed to decline over time, which leads to an increased vulnerability to infectious diseases and thus aging and death.

The rate of aging varies substantially across different species, and this, to a large extent, is genetically based. For example, numerous perennial plants ranging from strawberries and potatoes to willow trees typically produce clones of themselves by vegetative reproduction and are thus potentially immortal, while annual plants such as wheat and watermelons die each year and reproduce by sexual reproduction. The oldest animals known so far are 15,000-year-old Antarctic sponges,[6] which can reproduce both sexually and clonally.

Clonal immortality apart, there are certain species whose individual lifespans stand out among Earth's life-forms, including the bristlecone pine at around 5,000 years[7] invertebrates like the hard clam (known as quahog in New England) at 508 years,[8] the Greenland shark at 400 years,[9] various deep-sea tube worms at over 300 years,[10] and lobsters.[11] Such organisms are sometimes said to exhibit negligible senescence.[12]

An elderly Somali woman

Damage-related factors

Numerous damage-related factors have been proposed that lead to aging, including the following:[5]

Wear and tear theory

Cells and tissues have vital parts that wear out resulting in aging. Like components of an aging machine, parts of the body eventually wear out from repeated use, leading to cell death and inability to function.

Rate of living theory

This suggests that the greater an organism’s rate of oxygen basal metabolism, the shorter its life span. While helpful, this does not explain maximum life span.

Cross-linking theory

According to this theory, an accumulation of cross-linked proteins damages cells and tissues, slowing down bodily processes and resulting in aging.

Free radical theory

This proposes that free radicals cause damage to the macromolecular components of the cell, giving rise to accumulated damage causing cells, and eventually organs, to stop functioning. Macromolecules, such as nucleic acids, lipids, sugars, and proteins, are susceptible to free radical attack. Enzymes, which are natural antioxidants, are found in the body and function to curb build-up of free radicals.

Somatic DNA damage theory

DNA damage occurs continuously in cells of living organisms. While most of the damage is repaired naturally, some accumulates as the repair mechanisms cannot correct defects as fast as they are produced. Thus, aging results from damage to the genetic integrity of the body’s cells.

Other suggested factors include: progressive loss of physiological integrity through genomic instability (mutations accumulated in nuclear DNA, in mtDNA, and in the nuclear lamina) and telomere attrition.[13] Also, accumulation of waste products in cells presumably interferes with metabolism. For example, a waste product called lipofuscin is formed by a complex reaction in cells that binds fat to proteins. This waste accumulates in the cells as small granules, which increase in size as a person ages.[14]

Effects

Enlarged ears and noses of old humans are sometimes blamed on continual cartilage growth, but the cause is more probably gravity.[15]
Age dynamics of the body mass (1, 2) and mass normalized to height (3, 4) of men (1, 3) and women (2, 4).[16]
Comparison of a normal aged brain (left) and a brain affected by Alzheimer's disease (right).

In humans, aging represents the accumulation of changes in a human being over time and can encompass physical, psychological, and social changes. Reaction time, for example, may slow with age, while memories and general knowledge typically increase. Aging also increases the risk of diseases.

A number of characteristic aging symptoms are experienced by a significant proportion of human beings during their lifetimes, including the following:

  • After peaking in the mid-20s, female fertility declines.[17]
  • After age 30 the mass of human body is decreased until 70 years and then shows damping oscillations.[16]
  • Muscles have reduced capacity of responding to exercise or injury and loss of muscle mass and strength (sarcopenia) is common.[18]
  • Hand strength and mobility are decreased during the aging process. These things include "hand and finger strength and ability to control submaximal pinch force and maintain a steady precision pinch posture, manual speed, and hand sensation."[19]
  • People over 35 years of age are at increasing risk for losing strength in the ciliary muscle of the eyes which leads to difficulty focusing on close objects, or presbyopia.[20] Most people experience presbyopia by age 45–50.
  • Around age 50, hair turns grey. Pattern hair loss or baldness by the age of 50 affects about 50 percent of men and 25 percent of women.
  • Menopause typically occurs between 44 and 58 years of age.
  • In the 60–64 age cohort, the incidence of osteoarthritis rises.
  • Wrinkles develop mainly due to photoageing, particularly affecting sun-exposed areas (face).
  • Almost half of people older than 75 have hearing loss (presbycusis) inhibiting spoken communication.[21]
  • By age 80, more than half of all Americans either have a cataract or have had cataract surgery.[22]
  • Frailty, a syndrome of decreased strength, physical activity, physical performance and energy, affects 25 percent of those over 85.[23]
  • Atherosclerosis is classified as an aging disease, which leads to cardiovascular disease (for example stroke and heart attack), globally the most common causes of death.[24]
  • Dementia becomes more common with age. The spectrum ranges from mild cognitive impairment to the neurodegenerative diseases of Alzheimer's disease, cerebrovascular disease, Parkinson's disease and Lou Gehrig's disease. bout 3 percent of people between the ages of 65 and 74, 19 percent between 75 and 84, and nearly half of those over 85 years of age have dementia.[25] Furthermore, many types of memory decline with aging, but not semantic memory or general knowledge such as vocabulary definitions, which typically increases or remains steady until late adulthood.[26] Individual variations in rate of cognitive decline may be explained in terms of people having different lengths of life.[27]

Prevention and delay

Human beings who do not have a belief in an afterlife, the continued existence of an eternal spirit or soul after the death of their physical body, have sought ways to prevent aging and death, or at least to delay the process. Such research supports each individual's likelihood of living their full lifespan in good health. The following are factors which have been found to increase the length and quality of life.

Lifestyle

A healthy diet may reduce the effects of aging. For example, the Mediterranean diet is credited with lowering the risk of heart disease and early death. The major contributors to mortality risk reduction appear to be a higher consumption of vegetables, fish, fruits, nuts, and monounsaturated fatty acids (olive oil).[28]

Amount of sleep is related to mortality. People who live the longest report sleeping for six to seven hours each night, while the National Sleep Foundation recommends eight hours of sleep per night for optimal health. However, this range of sleep has not been shown to be causal in increasing life span, merely correlated with longer life which may be affected by various other factors. Studies linking longer or shorter sleep patterns to increased mortality do not necessarily imply that people should change their existing, and comfortable, sleep patterns. [29]

Physical exercise may increase life expectancy. People who participate in moderate to high levels of physical exercise have a lower mortality rate compared to individuals who are not physically active.[30] Moderate levels of exercise have been correlated with preventing aging and improving quality of life by reducing inflammatory potential.[31] Regular physical exercise has also been shown to have restorative properties for cognitive and brain function in old age.[32]

Avoidance of chronic stress (as opposed to acute stress) is associated with a slower loss of telomeres in most but not all studies, and with decreased cortisol levels, both of which are factors in increasing morbidity and mortality. Stress can be countered by social connection, spirituality, and (for men more clearly than for women) married life, all of which are associated with longevity.[33][34]

Medical intervention

Theoretically, extension of maximum lifespan in humans could be achieved by reducing the rate of aging damage by periodic replacement of damaged tissues, molecular repair or rejuvenation of deteriorated cells and tissues, reversal of harmful epigenetic changes, or the enhancement of enzyme telomerase activity. Research geared towards life extension strategies in various organisms is currently under way at a number of academic and private institutions. Various drugs and interventions have been shown to slow or reverse the biological effects of aging in animal models, but none has yet been proven to do so in humans.

Society and culture

An elderly man

Different cultures express age in different ways. Most legal systems define a specific age for when an individual is allowed or obliged to do particular activities. These age specifications include voting age, drinking age, age of consent, age of majority, age of criminal responsibility, marriageable age, age of candidacy, and mandatory retirement age. In other words, chronological aging may be distinguished from "social aging" (cultural age-expectations of how people should act as they grow older) and "biological aging" (an organism's physical state as it ages).[35]

Sociology

Christoffer Wilhelm Eckersberg: Ages of Man

In the fielda of sociology and mental health, ageing is seen in five different views: aging as maturity, aging as decline, aging as a life-cycle event, aging as generation, and aging as survival.[36] Positive correlates with aging often include economics, employment, marriage, children, education, and sense of control. Retirement, a common transition faced by the elderly, may have both positive and negative consequences.[37]

Population aging is the increase in the number and proportion of older people in society. Population aging occurs through migration, longer life expectancy (decreased death rate), and decreased birth rate. As a population ages, it has a significant impact on society. Young people tend to have fewer legal privileges (if they are below the age of majority), they are more likely to push for political and social change, to develop and adopt new technologies, and to need education. Older people have different requirements from society and government, and frequently have differing values as well, such as for property and pension rights.[38]

Economics

Among the most urgent concerns of older persons worldwide is income security. This poses challenges for governments with aging populations to ensure that investment in pension systems is sufficient to provide economic independence and reduce poverty in old age. These challenges vary for developing and developed countries:

Sustainability of these systems is of particular concern, particularly in developed countries, while social protection and old-age pension coverage remain a challenge for developing countries, where a large proportion of the labour force is found in the informal sector.[39]

Health care

With age inevitable biological changes occur that increase the risk of illness and disability. A number of health problems become more prevalent as people get older. These include mental health problems as well as physical health problems, especially dementia.

While the effects on society of population aging are multidimensional, there is no doubt about its impact on health care demand:

A life-cycle approach to health care – one that starts early, continues through the reproductive years and lasts into old age – is essential for the physical and emotional well-being of older persons, and, indeed, all people. Public policies and programmes should additionally address the needs of older impoverished people who cannot afford health care.[39]

Self-perception

As humans age, their bodies begin to break down, and among other changes their skin begins to look different. However, especially in Western culture, these changes are not always appreciated and being young, or at least youthful, is celebrated especially when young people are successful.[40]

Generally, aversion to aging and its effects is primarily a Western attitude. In other places around the world, old age is celebrated and honored. In Korea, for example, a special party called hwangap is held to celebrate and congratulate an individual for turning 60 years old.[41]

Positive self-perceptions of aging are associated with better mental and physical health and well-being.[42] Positive self-perception of health has been correlated with higher well-being and reduced mortality among the elderly. Various reasons have been proposed for this association; people who are objectively healthy may naturally rate their health better as than that of their ill counterparts.

As people age, subjective health remains relatively stable, even though objective health worsens. In fact, perceived health improves with age when objective health is controlled in the equation. This phenomenon is known as the "paradox of aging," and may be a result of social comparison; for instance, the older people get, the more they may consider themselves in better health than their same-aged peers. Elderly people often associate their functional and physical decline with the normal aging process.[43]

Successful aging

Traditional definitions of successful aging have emphasized absence of physical and cognitive disabilities.[44] Successful aging has been characterized as involving three components: a) freedom from disease and disability, b) high cognitive and physical functioning, and c) social and productive engagement.[45]

Notes

  1. 1.0 1.1 1.2 Roger B. McDonald, Biology of Aging (Garland Science, 2019, ISBN 0815345674).
  2. D. Harman, The aging process Proc Natl Acad Sci U S A 78(11) (November 1981): 7124–7128. Retrieved May 31, 2022.
  3. Stefan I. Liochev, Which Is the Most Significant Cause of Aging? Antioxidants (Basel) 4(4) (December 2015): 793–810. Retrieved May 31, 2022.
  4. Aleksey V. Belikov, Age-related diseases as vicious cycles Ageing Research Reviews 49 (January 2019): 11–26. Retrieved May 31, 2022.
  5. 5.0 5.1 Kunlin Jin, Modern Biological Theories of Aging Aging Dis. 1(2) (October 2010): 72–74. Retrieved May 31, 2022.
  6. Marnie Chesterton, The oldest living thing on Earth BBC News, June 12, 2017. Retrieved May 31, 2022.
  7. Oldlist Rocky Mountain Tree Ring Research. Retrieved May 31, 2022.
  8. Danuta Sosnowska, Chris Richardson, William E. Sonntag, Anna Csiszar, Zoltan Ungvari, and Iain Ridgway, A heart that beats for 500 years The Journals of Gerontology Series A, Biological Sciences and Medical Sciences 69(12) (December 2014): 1448–1461. Retrieved May 31, 2022.
  9. J. Nielsen, et al, Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus) Science 353(6300) (August 2016): 702–704. Retrieved May 31, 2022.
  10. Alanna Durkin, Charles R. Fisher, Erik E. Cordes, Extreme longevity in a deep-sea vestimentiferan tubeworm and its implications for the evolution of life history strategies The Science of Nature 104(7–8) (August 2017): 63. Retrieved May 31, 2022.
  11. Jacob Silverman, Is there a 400 pound lobster out there? How Stuff Works. Retrieved May 31, 2022.
  12. John C. Guerin, Emerging area of aging research: long-lived animals with "negligible senescence" Annals of the New York Academy of Sciences 1019(1) (June 2004): 518–520. Retrieved May 31, 2022.
  13. Carlos López-Otín, Maria A. Blasco, Linda Partridge, Manuel Serrano, and Guido Kroemer, The Hallmarks of Aging Cell 153(6) (June 2013): 1194–1217. Retrieved May 31, 2022.
  14. Edward J. Masoro and Steven N. Austad (eds.), Handbook of the Biology of Aging (Academic Press, 2006, ISBN 0120883872).
  15. Stephen Moss, Big ears: they really do grow as we age The Guardian, July 17, 2013. Retrieved May 31, 2022.
  16. 16.0 16.1 I. G. Gerasimov and Dmitry Yu Ignatov, Age Dynamics of Body Mass and Human Lifespan Journal of Evolutionary Biochemistry and Physiology 40(3) (2004):343–349. Retrieved May 31, 2022.
  17. Infertility: Overview Institute for Quality and Efficiency in Health Care, March 25, 2015. Retrieved May 31, 2022.
  18. James G. Ryall, Jonathan D. Schertzer, and Gordon S. Lynch, Cellular and molecular mechanisms underlying age-related skeletal muscle wasting and weakness Biogerontology 9(4) (August 2008): 213–228. Retrieved May 31, 2022.
  19. Vinoth K. Ranganathan, Vlodek Siemionow, Vinod Sahgal, and Guang H. Yue, Effects of Aging on Hand Function Journal of the American Geriatrics Society 49(11) (November 2001):1478–1484. Retrieved May 31, 2022.
  20. Refractive Errors National Eye Institute. Retrieved May 31, 2022.
  21. Hearing Loss and Older Adults National Institute on Deafness and Other Communication Disorders. Retrieved May 31, 2022.
  22. Cataracts National Eye Institute. Retrieved May 31, 2022.
  23. L.P. Fried, C.M. Tangen, J. Walston, A.B. Newman, C. Hirsch, J. Gottdiener, T. Seeman, R. Tracy, W.J. Kop, G. Burke, and M.A. McBurnie, Frailty in older adults: evidence for a phenotype The Journals of Gerontology Series A, Biological Sciences and Medical Sciences 56(3) (March 2001): M146-156. Retrieved May 31, 2022.
  24. The top 10 causes of death World Health Organization, December 9, 2020. Retrieved May 31, 2022.
  25. Rolando T. Lazaro, Sandra G. Reina-Guerra, and Myla Quiben, Umphred's Neurological Rehabilitation (Mosby, 2019, ISBN 0323611176).
  26. K. Warner Schaie, Developmental Influences on Adult Intelligence (Oxford University Press, 2012, ISBN 0195386132).
  27. Ian Stuart-Hamilton, The Psychology of Ageing: An Introduction (Jessica Kingsley Publishers, 2012, ISBN 184905245X).
  28. Mediterranean diet associated with lower risk of early death in cardiovascular disease patients European Society of Cardiology, August 29, 2016. Retrieved May 31, 2022.
  29. Rhonda Rowland, Experts challenge study linking sleep, life span CNN, February 15, 2002. Retrieved May 31, 2022.
  30. Claude Bouchard, Steven N. Blair, and William L. Haskell (eds.), Physical Activity and Health (Human Kinetics, 2012, ISBN 0736095411).
  31. Jeffrey A. Woods, Kenneth R. Wilund, Stephen A. Martin, and Brandon M. Kistler, Exercise, inflammation and aging Aging and Disease 3(1) (February 2012): 130–140. Retrieved May 31, 2022.
  32. Arthur F. Kramer and Kirk I. Erickson, Capitalizing on cortical plasticity: influence of physical activity on cognition and brain function Trends in Cognitive Sciences 11(8) (August 2007):342-348. Retrieved May 31, 2022.
  33. Harold Koenig, Dana King, and Verna B. Carson, Handbook of Religion and Health (Oxford University Press, 2012, ISBN 0195335953).
  34. Lecia Bushak, Married Vs Single: What Science Says Is Better For Your Health Medical Daily, April 2, 2015. Retrieved May 31, 2022.
  35. Judith Phillips, Kristine Ajrouch, and Sarah Hillcoat-Nallétamby, Key Concepts in Social Gerontology (SAGE Publications, 2010, ISBN 1412922720).
  36. Teresa L. Scheid and Eric R. Wright (eds.), A Handbook for the Study of Mental Health (Cambridge University Press, 2017, ISBN 9781316500965).
  37. Susan K. Whitbourne and Stacey B. Whitbourne, Adult Development and Aging (Wiley, 2020, ISBN 1119667453).
  38. John A. Vincent, Understanding generations: political economy and culture in an ageing society The British Journal of Sociology 56(4) (December 2005): 579–599. Retrieved May 31, 2022.
  39. 39.0 39.1 Jose Miguel Guzman, Ann Pawliczko, Sylvia Beales, Celia Till, and Ina Voelcker (ed.), Ageing in the Twenty-First Century: A Celebration and a Challenge (United Nations Population Fund, HelpAge International, 2012, ISBN 0897149815).
  40. Carolyn Gregoire, Here's Everything That's Wrong With Our 'Under 30' Obsession Huffington Post, February 25, 2014. Retrieved May 31, 2022.
  41. Korea - Birthday Celebrations Asian Info. Retrieved May 31, 2022.
  42. Serena Sabatini, Barbora Silarova, Anthony Martyr, Rachel Collins, Clive Ballard, Kaarin J. Anstey, Sarang Kim, and Linda Clare, Associations of Awareness of Age-Related Change With Emotional and Physical Well-being: A Systematic Review and Meta-analysis The Gerontologist 60(6) (August 2020): e477–e490. Retrieved May 31, 2022.
  43. Jutta Heckhausen, Developmental Regulation in Adulthood: Age-Normative and Sociostructural Constraints as Adaptive Challenges (Cambridge University Press, 2006, ISBN 0521027136).
  44. Paul B. Baltes and Margaret M. Baltes, Successful Aging (Cambridge University Press, 1993, ISBN 052143582X).
  45. J.W. Rowe and R.L. Kahn, Human aging: usual and successful Science 237(4811) (July 1987): 143–149. Retrieved May 31, 2022.

References
ISBN links support NWE through referral fees

  • Baltes, Paul B., and Margaret M. Baltes. Successful Aging. Cambridge University Press, 1993. ISBN 052143582X
  • Bouchard, Claude, Steven N. Blair, and William L. Haskell (eds.). Physical Activity and Health. Human Kinetics, 2012. ISBN 0736095411
  • Guzman, Jose Miguel, Ann Pawliczko, Sylvia Beales, Celia Till, and Ina Voelcker (eds.). Ageing in the Twenty-First Century: A Celebration and a Challenge. United Nations Population Fund, HelpAge International, 2012. ISBN 0897149815
  • Heckhausen, Jutta. Developmental Regulation in Adulthood: Age-Normative and Sociostructural Constraints as Adaptive Challenges. Cambridge University Press, 2006. ISBN 0521027136
  • Koenig, Harold, Dana King, and Verna B. Carson. Handbook of Religion and Health. Oxford University Press, 2012. ISBN 0195335953
  • Lazaro, Rolando T., Sandra G. Reina-Guerra, and Myla Quiben. Umphred's Neurological Rehabilitation. Mosby, 2019. ISBN 0323611176
  • Masoro, Edward J., and Steven N. Austad (eds.). Handbook of the Biology of Aging. Academic Press, 2006. ISBN 0120883872
  • McDonald, Roger B. Biology of Aging. Garland Science, 2019. ISBN 0815345674
  • Phillips, Judith, Kristine Ajrouch, and Sarah Hillcoat-Nallétamby. Key Concepts in Social Gerontology. SAGE Publications, 2010. ISBN 1412922720
  • Schaie, K. Warner. Developmental Influences on Adult Intelligence. Oxford University Press, 2012. ISBN 0195386132
  • Scheid, Teresa L., and Eric R. Wright (eds.). A Handbook for the Study of Mental Health. Cambridge University Press, 2017. ISBN 9781316500965
  • Stuart-Hamilton, Ian. The Psychology of Ageing: An Introduction. Jessica Kingsley Publishers, 2012. ISBN 184905245X
  • Whitbourne, Susan K., and Stacey B. Whitbourne. Adult Development and Aging. Wiley, 2020. ISBN 1119667453

External links

All links retrieved June 16, 2023.

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