Caffeine

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Caffeine
Caffeine Caffeine
General
IUPAC nomenclature 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione
Other names 1,3,7-trimethylxanthine
trimethylxanthine
theine
mateine
guaranine
methyltheobromine
Molecular formula C8H10N4O2
SMILES O=C1C2=C(N=CN2C)N(C(=O)N1C)C
Molar mass 194.19 g/mol
Appearance Odorless, white needles or powder
CAS number [58-08-2]
Properties
Density and phase 1.2 g/cm3, solid
Solubility in water Slightly soluble
Melting point 237 °C
Boiling point 178 °C (sublimes)
Acidity (pKa) 10.4
Hazards
MSDS External MSDS
Main hazards May be fatal if inhaled, swallowed
or absorbed through the skin.
NFPA 704

NFPA 704.svg

1
2
0
 
Flash point N/A
RTECS number EV6475000
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Caffeine is a naturally occuring chemical found only in certain plants. At present, there are 63 different types of plants known to contain caffeine[1], which include the plants from which we obtain coffee,tea and cocoa. Historically the most popular source of caffeine in the human diet has been from coffee and tea. Today, beverages containing added caffeine — such as colas and energy drinks — enjoy popularity great enough to make caffeine the world's most popular psychoactive drug.

Other, less commonly used sources of caffeine include the plants yerba mate and guaraná, which are sometimes used in the preparation of teas and, more recently, energy drinks.

Caffeine is classified as a xanthine alkaloid. In its pure form it is a white powder that is odorless with a slightly bitter taste.

The name caffeine is derived apparently from the Italian word caffè for ("coffee") plus the alkaloid suffix -ine. Caffeine is a central nervous system (CNS) stimulant, having the effect of restoring alertness.

In nature, caffeine is found in widely varying concentrations with other xanthine alkaloids such as theophylline and theobromine, which are also cardiac stimulants.

Sources of caffeine

Caffeine is the most widely used psychoactive substance in the world.

The world's primary source of caffeine is the coffee bean (the seed of the coffee plant), from which coffee is brewed. More than 80 species of the genus Coffea are known. Caffeine content in coffee varies widely depending on the variety of coffee bean and the method of preparation used, but in general one 8oz serving of coffee has about 100 mg of caffeine. Generally, dark roast coffee has less caffeine than lighter roasts since the roasting process reduces caffeine content of the bean. Arabica coffee beans average 24 mg/g caffeine wheras the Robusta variety averages 13 mg/g (Casal et al.2000).

Tea is another common source of caffeine ,produced by brewing leaves of the tea plant. There are hundreds of varieties of this single species of tea,Camellia sinensis. The amount of oxidation that each variety undergoes determines whether it is classed as white,green,oolong or black,where white has the least amount of oxidation of the leaf and black tea has the most. More oxidation results in higher levels of caffeine. In black tea caffeine was found to be 25 mg/g of tea leaf whereas in green tea the caffeine level was 15 mg/g of leaf (Khokhar et al.2002).

Guarana beverages are made from seeds that have been ground and dissolved in hot water, similar to the process for brewing coffee. The plant is named after the South American Guarani tribes who are the earliest known consumers of the plant. The guarana seeds contain larger amounts of caffeine than do coffee beans.

Chocolate derived from cocoa is a weak stimulant which contains a small amount of caffeine.[2] However, chocolate contains too few alkaloids for a reasonable serving to create effects in humans that are on par with coffee. A typical serving of a milk chocolate bar (28g) has about 20 mg of caffeine.

Kola nuts are also a natural source of caffeine

Yerba Mate....

Caffeine is also a common additive of soft drink such as colas, which were originally prepared using kola nuts as the sole source of caffeine. Soft drinks like Coca-Cola Classic contain 23 mg per 8oz [3],and Pepsi One contains 36 mg per 8oz.[4] The U.S. Food and Drug Administration (F.D.A.) allows caffeine to be added to cola-type beverages up 0.02 % and it must appear on the label as an ingredient. The European Union requires that a warning be placed on the packaging of any food whose caffeine content exceeds 150 mg per litre.

History of caffeine use

Coffee beans are indigenous to the land of Ethiopia, and by the fourth century AD, were introduced to Arabia and the rest of the East.[5]In the 15th century the Sufis of Yemen used coffee to stay awake during prayers. In the 16th century there were coffee houses in Istanbul, Cairo and Mecca, and in 1573 coffee was introduced to the Europeans.

Tea has been consumed in China for thousands of years, where it has been purported to have been discovered by the Chinese Emperor Shen Nung in 2737 B.C.E. Traditional stories tell that monks drank tea to stay awake during meditation practice.

Cocoa,a beverage made from the seeds of the cacao plant was consumed by the Aztec leader Montezuma.

Milk chocolate was introduced into Switzerland in 1876. [6]

In 1819, relatively pure caffeine was isolated for the first time by the German chemist Friedrich Ferdinand Runge. According to the legend, he did this at the instigation of Johann Wolfgang von Goethe (Weinberg & Bealer 2001).

As of today, global consumption of caffeine has been estimated to be 120,000 tonnes per annum.[7] This is equivalent to every person on the planet consuming 50 mg of caffeine every day of the year.


Caffeine's toxicity to humans

There has been extensive research on caffeine and this drug’s effect on the health of human beings . The Food and Drug Administration (F.D.A.) concluded in 1958 that caffeine is recognized as safe for consumption. A recent review claims to have found no signs or evidence that caffeine’s use in carbonated beverages would produce unhealthy effects on the consumer.

The American Medical Association (AMA) also views caffeine as being safe for consumption. They state that moderate coffee and tea drinkers probably don’t need to have concern for their health in regards to caffeine consumption.[8]

Effects of caffeine

Caffeine has a significant effect on spiders, which is reflected in their web construction.

Caffeine is a central nervous system stimulant, and is used both recreationally and medically to restore mental alertness when unusual weakness or drowsiness occurs. Doses of 100-200 mg result in increased alertness and wakefulness, faster and clearer flow of thought, increased focus, and better general body coordination. It also results in restlessness, a loss of fine motor control, headaches, and dizziness.[9] It is important to note, however, that caffeine cannot replace sleep, and should be used only occasionally as an alertness aid.

Caffeine is sometimes administered in combination with medicines to increase their effectiveness, such as with ergotamine in the treatment of migraine and cluster headaches, or with certain pain relievers such as aspirin or acetaminophen. Caffeine may also be used to overcome the drowsiness caused by antihistamines. Breathing problems (apnea) in premature infants are sometimes treated with citrated caffeine, which is available only by prescription in many countries.

While relatively safe for humans, caffeine is considerably more toxic to some other animals such as dogs, horses and parrots due to a much poorer ability to metabolize this compound. Caffeine has a much more significant effect on spiders, for example, than most other drugs do. [10]

Caffeine metabolism

Caffeine is completely absorbed by the stomach and small intestine within 45 minutes of ingestion. After ingestion, caffeine has a physiological half-life of three and a half to six hours.[11] It is widely distributed in total body water and is eliminated by apparent first-order kinetics that can be described by a one-compartment open-model system. Continued consumption of caffeine can lead to tolerance. Upon withdrawal, the body becomes oversensitive to adenosine, causing the blood pressure to drop dramatically, which causes headaches and other symptoms.

Caffeine is metabolized in the liver by the cytochrome P450 oxidase enzyme system into three metabolic dimethylxanthines, which each have their own effects on the body:

  • Paraxanthine (84%) – Has the effect of increasing lipolysis, leading to elevated glycerol and free fatty acid levels in the blood plasma.
  • Theobromine (12%) – Dilates blood vessels and increases urine volume. Theobromine is also the principal alkaloid in cocoa, and therefore chocolate.
  • Theophylline (4%) – Relaxes smooth muscles of the bronchi, and is used to treat asthma. The therapeutic dose of theophylline, however, is many times greater than the levels attained from caffeine metabolism.

Each of these metabolites is further metabolised and then excreted in the urine.

Mechanism of action

The caffeine molecule is structurally similar to adenosine, and binds to adenosine receptors on the surface of cells without activating them (a "false transmitter" method of antagonism). This may be relevant in its diuretic properties, since adenosine is known to constrict preferentially the afferent arterioles of the glomerular apparatus; inhibition may cause vasodilation, with an increase in renal blood flow (RBF) and glomerular filtration rate (GFR). In the brain, adenosine binding also causes blood vessels to dilate (presumably to let more oxygen in during sleep).[12] This effect, called competitive inhibition, interrupts a pathway that normally serves to regulate nerve conduction by suppressing post-synaptic potentials. The result is an increase in the levels of epinephrine or adrenaline and norepinephrine released via the hypothalamic-pituitary-adrenal axis[13] Epinephrine, the natural endocrine response to a perceived threat, stimulates the sympathetic nervous system, leading to an increased heart rate, blood pressure and blood flow to muscles, a decreased blood flow to the skin and inner organs and a release of glucose by the liver.

Caffeine is also a known competitive inhibitor of the enzyme cAMP-phosphodiesterase (cAMP-PDE), which converts cyclic AMP (cAMP) in cells to its noncyclic form, allowing cAMP to build up in cells. Cyclic AMP participates in the messaging cascade produced by cells in response to stimulation by epinephrine, so by blocking its removal caffeine intensifies and prolongs the effects of epinephrine and epinephrine-like drugs such as amphetamine, methamphetamine, or methylphenidate.

The metabolites of caffeine contribute to caffeine's effects. Theobromine is a vasodilator that increases the amount of oxygen and nutrient flow to the brain and muscles. Theophylline, the second of the three primary metabolites, acts as a smooth muscle relaxant that chiefly affects bronchioles and acts as a chronotrope and inotrope that increases heart rate and efficiency. The third metabolic derivative, paraxanthine, is responsible for an increase in the lipolysis process, which releases glycerol and fatty acids into the blood to be used as a source of fuel by the muscles (Dews et al. 1984).

With these effects, caffeine is considered an ergogenic: increasing the capacity for mental or physical labor. A study conducted in 1979 showed a 7% increase in distance cycled over a period of two hours in subjects who consumed caffeine compared to control tests (Ivy et al. 1979). Other studies attained much more dramatic results; one particular study of trained runners showed a 44% increase in "race-pace" endurance, as well as a 51% increase in cycling endurance, after a dosage of 9 milligrams of caffeine per kilogram of body weight (Graham & Spriet 1991). The extensive boost shown in the runners is not an isolated case; additional studies have reported similar effects. Another study found 5.5 milligrams of caffeine per kilogram of body mass resulted in subjects cycling 29% longer during high intensity circuits (Trice & Hayes 1995).

Side effects of caffeine

The minimum lethal dose of caffeine ever reported is 3,200 mg, administered intravenously. The LD50 of caffeine is estimated between 13 and 19 grams for oral administration for an average adult. The LD50 of caffeine is dependent on weight and individual sensitivity and estimated to be about 150 to 200 mg per kg of body mass, roughly 140 to 180 cups of coffee for an average adult taken within a limited timeframe that is dependent on half-life. The half-life, or time it takes for the amount of caffeine in the blood to decrease by 50%, ranges from 3.5 to 10 hours. In adults the half-life is generally around 5 hours. However, contraceptive pills increase this to around 12 hours, and, for women over 3 months pregnant, it varies from 10 to 18 hours. In infants and young children, the half-life may be longer than in adults. With common coffee and a very rare half-life of 100 hours, it would require 3 cups of coffee every hour for 100 hours just to reach LD50. Though achieving lethal dose with coffee would be exceptionally difficult, there have been many reported deaths from intentional overdosing on caffeine pills.

Too much caffeine, especially over an extended period of time, can lead to a number of physical and mental conditions. The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) states: "The 4 caffeine-induced psychiatric disorders include caffeine intoxication, caffeine-induced anxiety disorder, caffeine-induced sleep disorder, and caffeine-related disorder not otherwise specified (NOS)."

An overdose of caffeine can result in a state termed caffeine intoxication or caffeine poisoning. Its symptoms are both physiological and psychological. Symptoms of caffeine intoxication include: restlessness, nervousness, excitement, insomnia, flushed face, diuresis, muscle twitching, rambling flow of thought and speech, paranoia, cardiac arrhythmia or tachycardia, and psychomotor agitation, gastrointestinal complaints, increased blood pressure, rapid pulse, vasoconstriction (tightening or constricting of superficial blood vessels) sometimes resulting in cold hands or fingers, increased amounts of fatty acids in the blood, and an increased production of gastric acid. In extreme cases mania, depression, lapses in judgment, disorientation, loss of social inhibition, delusions, hallucinations and psychosis may occur.[14]

It is commonly assumed that only a small proportion of people exposed to caffeine develop symptoms of caffeine intoxication. However, because it mimics organic mental disorders, such as panic disorder, generalized anxiety disorder, bipolar disorder, and schizophrenia, a growing number of medical professionals believe caffeine-intoxicated people are routinely misdiagnosed and unnecessarily medicated. Shannon et al (1998) point out that:

"Caffeine-induced psychosis, whether it be delirium, manic depression, schizophrenia, or merely an anxiety syndrome, in most cases will be hard to differentiate from other organic or non-organic psychoses....The treatment for caffeine-induced psychosis is to withhold further caffeine." A study in the British Journal of Addiction declared that "although infrequently diagnosed, caffeinism is thought to afflict as many as one person in ten of the population" (JE James and KP Stirling, 1983).

Because caffeine increases the production of stomach acid, high usage over time can lead to peptic ulcers, erosive esophagitis, and gastroesophageal reflux disease.Template:Citeneeded Furthermore, it can also lead to nervousness, irritability, anxiety, tremulousness, muscle twitching, insomnia, heart palpitations and hyperreflexia.[15]

It is suggested that "slow metabolizers" who carry a variant of polymorphic cytochrome P450 1A2 (CYP1A2) enzyme have an increased risk of nonfatal myocardial infarction (see references).

Withdrawal

Individuals who consume caffeine regularly develop a reduction in sensitivity to caffeine; when such individuals reduce their caffeine intake, their body becomes oversensitive to adenosine, with the result that blood pressure drops dramatically, leading to an excess of blood in the head (though not necessarily on the brain), causing a headache. Other symptoms may include nausea, fatigue, drowsiness, anxiety and irritability; in extreme cases symptoms may include depression, inability to concentrate and diminished motivation to initiate or to complete daily tasks at home or at work.

Withdrawal symptoms may appear within 12 to 24 hours after discontinuation of caffeine intake, peak at roughly 48 hours, and usually lasts from one to five days. Analgesics, such as aspirin, can relieve the pain symptoms, as can a small dose of caffeine.

Currently caffeine withdrawal is recognized as meriting further study by the DSM-IV, although recent research demonstrating its clinical significance means that it will likely be included as an Axis-1 disorder in the DSM-V [16]

Effects on fetuses and newborn children

There is some evidence that caffeine may be dangerous for fetuses and newborn children. In animal studies, caffeine intake during pregnancy has been demonstrated to have teratogenic effects and increase the risk of learning problems and hyperactivity in rats and mice, respectively. The applicability of these results to human infants is disputed since the concentrations involved were high and rodents are more susceptible to most mutagens. In a 1985 study conducted by scientists of Carleton University, Canada, children born by mothers who had consumed more than 300 mg/d caffeine (about 3 cups of coffee or 6 cups of tea) were found to have, on the average, lower birth weight and head circumference than the children of mothers who had consumed little or no caffeine. In addition, use of large amounts of caffeine by the mother during pregnancy may cause problems with the heart rhythm of the fetus. For these reasons, some doctors recommend that women largely discontinue caffeine consumption during pregnancy and possibly also after birth until the newborn child is weaned.

The negative effects of caffeine on the developing fetus can be attributed to the ability of caffeine to inhibit two DNA damage response proteins known as Ataxia-Telangiectasia Mutated (ATM) or ATM-Rad50 Related (ATR). These proteins control much of the cells' ability to stop cell cycle in the presence of DNA damage, such as DNA single/double strand breaks and nucleotide dimerization. DNA damage can occur relatively frequently in actively dividing cells, such as those in the developing fetus. Caffeine is used in laboratory setting as an inhibitor to these proteins and it has been shown in a study by Lawson et al. in 2004, that women who use caffeine during pregnancy have a higher likelihood of miscarriage than those who do not. Since the dosage rate of self-administration is difficult to control and the effects of caffeine on the fetus are related to random occurrence (DNA damage), a minimal toxic dose to the fetus has yet to be established.

Caffeine pills

Caffeine pills are often used by college students and shift workers as a convenient way to fight sleep, and are often considered harmless. However, like any medication, caffeine can be harmful or deadly in sufficient quantities. Due to the amount of caffeine present in standard pills, it is possible to consume a dangerous amount of caffeine in this form.

Periodically, caffeine pills come under media fire in connection with the death of a college student due to a large overdose of caffeine. One example is the death of a North Carolina student, Jason Allen, who swallowed most of a bottle of 90 such pills[17], equivalent to about 250 cups of coffee. A few other deaths by caffeine overdose have been known, almost always in the case of excessive pill consumption.

Extraction of pure caffeine

Caffeine extraction is an important industrial process and can be performed using a number of different solvents. Benzene, chloroform, trichloroethylene and dichloromethane have all been used over the years but for reasons of safety, environmental impact, cost and flavour, they have been superseded by two main methods:water and carbon dioxide.


Coffee beans are soaked in water. The water—which contains not only caffeine but also many other compounds which contribute to the flavour of coffee—is then passed through activated charcoal, which removes the caffeine. The water can then be put back with the beans and evaporated dry, leaving decaffeinated coffee with a good flavor. Coffee manufacturers recover the caffeine and resell it for use in soft drinks and medicines.

Supercritical carbon dioxide extraction of caffeine

Supercritical carbon dioxide is an excellent nonpolar solvent for caffeine (as well as many other organic compounds) but is safer than the organic solvents that are used for caffeine extraction. The extraction process is simple: CO2 is forced through the green coffee beans at temperatures above 31.1°C and pressures above 73 atm. Under these conditions, CO2 is said to be in a "supercritical" state: it has gaslike properties which allow it to penetrate deep into the beans but also liquid-like properties which dissolve 97-99% of the caffeine. The caffeine-laden CO2 is then sprayed with high pressure water to remove the caffeine. The caffeine can then be isolated by charcoal adsorption (as above) or by distillation, recrystallization, or reverse osmosis.

References
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  1. ↑ http://www.phytomedical.com/plant/caffeine.asp
  2. ↑ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15549276
  3. ↑ http://www2.coca-cola.com/ourcompany/al_facts_caffeine.html
  4. ↑ http://www.pepsi.com/pepsi_brands/ingredient_facts/index.php
  5. ↑ http://www.abc.net.au/quantum/poison/caffeine/caffeine.htm
  6. ↑ http://web1.caryacademy.org/chemistry/rushin/StudentProjects/CompoundWebSites/1998/Caffeine/history_of_caffeine.htm
  7. ↑ http://www.abc.net.au/quantum/poison/caffeine/caffeine.htm
  8. ↑ http://www.ific.org/publications/brochures/caffeinebroch.cfm
  9. ↑ http://mass-spec.chem.cmu.edu/VMSL/Caffeine/Caffeine_effects.htm
  10. ↑ Noever, R., J. Cronise, and R. A. Relwani. 1995. Using spider-web patterns to determine toxicity. NASA Tech Briefs 19(4):82. Published in New Scientist magazine, 27 April 1995.
  11. ↑ http://www.garynull.com/Documents/CaffeineEffects.htm
  12. ↑ http://home.howstuffworks.com/caffeine.htm
  13. ↑ http://pharmrev.aspetjournals.org/cgi/content/full/51/1/83
  14. ↑ http://www.nlm.nih.gov/medlineplus/ency/article/002579.htm
  15. ↑ http://www.coffeefaq.com/caffaq.html#CaffeineAndHealth
  16. ↑ http://www.cbsnews.com/stories/2004/09/30/health/webmd/main646620.shtml
  17. ↑ http://www.collegepublisher.com/media/paper87/DFPArchive/science/1103981.html
  • Casal,S.,Oliveira,M.B.P.P.,Alves,M.R.,and Ferreira,M.A. 2000. Discriminate analysis of roasted coffee varieties for trigonelline,nicotinic acid and caffeine content.Journal of Agricultural and Food Chemistry48:3420-3424
  • Cornelis MC, El-Sohemy A, Kabagambe EK, Campos H. Coffee, CYP1A2 genotype, and risk of myocardial infarction JAMA. 2006 Mar 8;295(10):1135-41 PMID 16522833
  • Dews, P.B. (1984). "Caffeine: Perspectives from Recent Research". Berlin: Springer-Valerag.
  • Hughes JR, McHugh P, Holtzman S. "Caffeine and schizophrenia." Psychiatr Serv 1998;49:1415-7. Fulltext. PMID 9826240.
  • Ivy, J., Costill, D., Fink, W. et al. (1979). "Influence of caffeine and carbohydrate feedings on endurance performance". Medical Science Sports Journal (Vol. 11). 6-11.
  • James,J.E. and Stirling,K.P., "Caffeine: A Summary of Some of the Known and Suspected Deleterious Habits of Habitual Use," British Journal of Addiction, 1983;78:251-58.
  • Khokhar,S. and Magnusdottir,S.G.M. 2002. Total penol,catechin,and caffeine contents of teas commonly consumed in the United Kingdom.Journal of Agricultural and Food Chemistry50:565-570.


  • Shannon MW, Haddad LM, Winchester JF. Clinical Management of Poisoning and Drug Overdose, 3rd ed.. 1998. ISBN 0721664091.
  • Diagnostic and Statistical Manual of Mental Disorders ISBN 0890420610
  • Tarnopolsky, M. A. (1994). "Caffeine and endurance performances". Sports Medicine (Vol. 18 Ed. 2): 109 – 125.
  • Trice, I., and Haymes, E. (1995). "Effects of caffeine ingestion on exercise-induced changes during high intensity, intermittent exercise". International Journal of Sports Nutrition. 37-44.
  • Weinberg BA, Bealer BK. The world of caffeine. New York & London: Routledge, 2001. ISBN 0-415-92722-6.

External links


Caffeine toxicity


Stimulants (N06 and others) - edit

Caffeine | Nicotine | Modafinil/Armodafinil | Adrafinil | Fenethylline

Sympathomimetic amines (R01, A08, and others) - edit

4-methylaminorex | Benzylpiperazine | Cathinone | Chlorphentermine | Cocaine | CFT | Diethylpropion | Ephedrine | Fenfluramine | Mazindol | Methylone | Methylphenidate | Pemoline | Phendimetrazine | Phenmetrazine | Phentermine | Phenylephrine | Propylhexedrine | Pseudoephedrine | Sibutramine | Synephrine

See also amphetamines

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