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- Main article: tocopherol
Vitamin E is the collective name for a set of 8 related tocopherols and tocotrienols, which are fat-soluble vitamins with antioxidant properties. 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.
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. 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.
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, and tocotrienols may have a specialized role in protecting neurons from damage. However, the roles and importance of the various forms of vitamin E are presently unclear, 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.
Most studies about Vitamin E have supplemented only alpha-tocopherol, but doing so leads to reduced serum gamma- and delta-tocopherol concentrations. 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:
- Red Palm Oil
- Spinach and other green leafy vegetables
- Vegetable oils -- Canola, corn, sunflower, soybean, cottonseed
- Wheat germ
- Wholegrain foods
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 by 30 percent. 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. 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.
- 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.
- 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.
- 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.
- USDA National Nutrient Database
- 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
- 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
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