The a-tocopherol form of vitamin E.
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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, a-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 a-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 a-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 ?-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.
Food sources of Vitamin E
Particularly high levels of vitamin E can be found in the following foods:
Source: USDA National Nutrient Database
References
- ^ a b Herrera E, Barbas C (2001). "Vitamin E: action, metabolism and perspectives". J Physiol Biochem 57 (2): 43 – 56. PMID 11579997.
- ^ 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.
- ^ a b Brigelius-Flohé R, Traber M (1999). "Vitamin E: function and metabolism". FASEB J 13 (10): 1145 – 55. PMID 10385606.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ Zingg JM, Azzi A (2004). "Non-antioxidant activities of vitamin E". Curr. Med. Chem. 11 (9): 1113–33. PMID 15134510.
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