Vitamin E - Wikipedia, the free encyclopedia

Vitamin E

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The α-tocopherol form of vitamin E.
Main articles: tocopherol and tocotrienol

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.

Contents

[edit] Food sources of Vitamin E

Particularly high levels of vitamin E can be found in the following foods:[11]

[edit] 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]

[edit] References

  1. ^ a b 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, http://jn.nutrition.org/cgi/content/full/131/2/369S. 
  3. ^ a b Brigelius-Flohé R, Traber M (1999). "Vitamin E: function and metabolism". FASEB J 13 (10): 1145 – 55. PMID 10385606, http://www.fasebj.org/cgi/content/full/13/10/1145. 
  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, http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1790869&blobtype=pdf. 
  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. ^ a b 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

[edit] External links

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