Vitamin E
Vitamin E is the collective name for a set of 8 related tocopherols and tocotrienols, which are fat-soluble vitamins with antioxidant properties.[1][2] Of these, α-tocopherol (also written as alpha-tocopherol) has been most studied as it has the highest bioavailability, with the body preferentially absorbing and using this form.[3]
It has been claimed that α-tocopherol is the most important lipid-soluble antioxidant, and that it protects cell membranes from oxidation by reacting with lipid radicals produced in the lipid peroxidation chain reaction.[1][4] This would remove the free radical intermediates and prevent the oxidation reaction from continuing. The oxidised α-tocopheroxyl radicals produced in this process may be recycled back to the active reduced form through reduction by other antioxidants, such as ascorbate, retinol or ubiquinol.[5]
The functions of the other forms of vitamin E are less well-studied, although γ-tocopherol (also written as gamma-tocopherol) is a nucleophile that may react with electrophilic mutagens[3] and the tocotrienols having specialized roles in protecting neurons from damage[6], cancer prevention[7] and cholesterol reduction[8]. However, the roles and importance of all of the various forms of vitamin E are presently unclear,[9][10] and it has even been suggested that the most important function of vitamin E is as a signaling molecule, and that it has no significant role in antioxidant metabolism.[11][12]
Most studies about vitamin E have supplemented using only the synthetic alpha-tocopherol, but doing so leads to reduced serum gamma- and delta-tocopherol concentrations. Moreover, a 2007 clinical study involving synthetic alpha-tocopherol concluded that supplementation did not reduce the risk of major cardiovascular events in middle aged and older men[13]. For more info, read article tocopherol.
1 IU of vitamin E is the biological equivalent of about 0.667 mg d-alpha-tocopherol (2/3 mg exactly), or of 1 mg of dl-alpha-tocopherol acetate.
Food sources of Vitamin E
Particularly high levels of vitamin E can be found in the following foods:[14]
- Almonds
- Asparagus
- Avocado
- Nuts
- Olives
- Red Palm Oil
- Seeds
- Spinach and other green leafy vegetables
- Vegetable oils — Canola, corn, sunflower, soybean, cottonseed
- Wheat germ
- Wholegrain foods
- Milk
Vitamin E and prostate cancer study discontinued
There have been some theories that Vitamin E, especially when coupled with selenium, may reduce the risk of prostate cancer[15] by 30 percent.[16] However, the Selenium and Vitamin E Cancer Prevention Trial, ("SELECT"), run from 2004 to 2008, found that vitamin E, whether taken alone or in combination with selenium, did not prevent prostate cancer.[17] The SELECT study was discontinued after independent reviewers determined that there was no benefit to the 35,000 men who were the subject of the study.[15]
ReferencesISBN links support NWE through referral fees
- ↑ 1.0 1.1 Herrera E, Barbas C (2001). Vitamin E: action, metabolism and perspectives. J Physiol Biochem 57 (2): 43 – 56.
- ↑ Packer L, Weber SU, Rimbach G (2001). Molecular aspects of alpha-tocotrienol antioxidant action and cell signalling. J. Nutr. 131 (2): 369S–73S.
- ↑ 3.0 3.1 Brigelius-Flohé R, Traber M (1999). Vitamin E: function and metabolism. FASEB J 13 (10): 1145 – 55.
- ↑ Traber MG, Atkinson J (2007). Vitamin E, antioxidant and nothing more. Free Radic. Biol. Med. 43 (1): 4–15.
- ↑ Wang X, Quinn P (1999). Vitamin E and its function in membranes. Prog Lipid Res 38 (4): 309 – 36.
- ↑ Sen C, Khanna S, Roy S (2006). Tocotrienols: Vitamin E beyond tocopherols. Life Sci 78 (18): 2088 – 98.
- ↑ Malafa MP (2008). New insights and gains in pancreatic cancer. Cancer Control 15 (4).
- ↑ Das, S., I. Lekli, et al. (2008). Cardioprotection with palm oil tocotrienols: comparision of different isomers.. Am J Physiol Heart Circ Physiol 294 (2).
- ↑ Brigelius-Flohé R, Davies KJ (2007). Is vitamin E an antioxidant, a regulator of signal transduction and gene expression, or a 'junk' food? Comments on the two accompanying papers: "Molecular mechanism of alpha-tocopherol action" by A. Azzi and "Vitamin E, antioxidant and nothing more" by M. Traber and J. Atkinson. Free Radic. Biol. Med. 43 (1): 2–3.
- ↑ Atkinson J, Epand RF, Epand RM (2007). Tocopherols and tocotrienols in membranes: A critical review. Free Radic. Biol. Med. 44 (5): 739–764.
- ↑ Azzi A (2007). Molecular mechanism of alpha-tocopherol action. Free Radic. Biol. Med. 43 (1): 16–21.
- ↑ Zingg JM, Azzi A (2004). Non-antioxidant activities of vitamin E. Curr. Med. Chem. 11 (9): 1113–33.
- ↑ Sesso, H.D., et al (2008). Vitamins E and C in the Prevention of Cardiovascular Disease in Men: The Physicians' Health Study II Randomized Controlled Trial. JAMA 300 (18).
- ↑ USDA National Nutrient Database
- ↑ 15.0 15.1 American Cancer Society, Vitamin E, updated Oct. 27, 2008
- ↑ National Cancer Institute, The SELECT Prostate Cancer Prevention Trial, Oct. 27, 2008
- ↑ National Cancer Institute, Selenium and Vitamin E Cancer Prevention Trial (SELECT), Oct. 31, 2008
External links
- Vitamin E Medline Plus, Medical Encyclopedia, U.S. National Library of Medicine
- Vitamin E Office of Dietary Supplements, National Institutes of Health
- Jane Higdon, "Vitamin E", Micronutrient Information Center, Linus Pauling Institute
| Vitamins |
|---|
| All B vitamins | All D vitamins |
| Retinol (A) | Thiamine (B1) | Riboflavin (B2) | Niacin (B3) | Pantothenic acid (B5) | Pyridoxine (B6) | Biotin (B7) | Folic acid (B9) | Cyanocobalamin (B12) | Ascorbic acid (C) | Ergocalciferol (D2) | Cholecalciferol (D3) | Tocopherol (E) | Naphthoquinone (K) |
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