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Vitamin E

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File:Tocopherol, alpha-.svg

The α-tocopherol form of vitamin E.

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.[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 tocotrienols may have a specialized role in protecting neurons from damage.[6] However, the roles and importance of the various forms of vitamin E are presently unclear,[7][8] 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.[9][10]

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:[11]

  • 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[12] by 30 percent.[13] 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.[14] 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.[12]

References[]

  1. ↑ 1.0 1.1 Herrera E, Barbas C (2001). Vitamin E: action, metabolism and perspectives. J Physiol Biochem 57 (2): 43 – 56. PMID: 11579997.
  2. ↑ Packer L, Weber SU, Rimbach G (2001). Molecular aspects of alpha-tocotrienol antioxidant action and cell signalling. J. Nutr. 131 (2): 369S–73S. PMID: 11160563.
  3. ↑ 3.0 3.1 Brigelius-Flohé R, Traber M (1999). Vitamin E: function and metabolism. FASEB J 13 (10): 1145 – 55. PMID: 10385606.
  4. ↑ Traber MG, Atkinson J (2007). Vitamin E, antioxidant and nothing more. Free Radic. Biol. Med. 43 (1): 4–15. DOI: 10.1016/j.freeradbiomed.2007.03.024. PMID: 17561088.
  5. ↑ Wang X, Quinn P (1999). Vitamin E and its function in membranes. Prog Lipid Res 38 (4): 309 – 36. DOI: 10.1016/S0163-7827(99)00008-9. PMID: 10793887.
  6. ↑ Sen C, Khanna S, Roy S (2006). Tocotrienols: Vitamin E beyond tocopherols. Life Sci 78 (18): 2088 – 98. DOI: 10.1016/j.lfs.2005.12.001. PMID: 16458936.
  7. ↑ 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. PMID: 17561087.
  8. ↑ Atkinson J, Epand RF, Epand RM (2007). Tocopherols and tocotrienols in membranes: A critical review. Free Radic. Biol. Med. 44 (5): 739–764. DOI: 10.1016/j.freeradbiomed.2007.11.010. PMID: 18160049.
  9. ↑ Azzi A (2007). Molecular mechanism of alpha-tocopherol action. Free Radic. Biol. Med. 43 (1): 16–21. DOI: 10.1016/j.freeradbiomed.2007.03.013. PMID: 17561089.
  10. ↑ Zingg JM, Azzi A (2004). Non-antioxidant activities of vitamin E. Curr. Med. Chem. 11 (9): 1113–33. PMID: 15134510.
  11. ↑ USDA National Nutrient Database
  12. ↑ 12.0 12.1 American Cancer Society, Vitamin E, updated Oct. 27, 2008
  13. ↑ National Cancer Institute, The SELECT Prostate Cancer Prevention Trial, Oct. 27, 2008
  14. ↑ 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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