Vitamin E

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Vitamin E is a generic term for tocopherols and tocotrienols.^[1] Vitamin E is a family of α-, β-, γ-, and δ-tocopherols and corresponding four tocotrienols. Vitamin E is a fat-soluble antioxidant that stops the production of reactive oxygen species formed when fat undergoes oxidation.^[2][3][4] Of these, α-tocopherol (also written as alpha-tocopherol) has been most studied as it has the highest bioavailability.^[5]

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.^[3][6] 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.^[7] However, the importance of the antioxidant properties of this molecule at the concentrations present in the body are not clear and it is possible that the reason why vitamin E is required in the diet is unrelated to its ability to act as an antioxidant.^[8]. Other forms of vitamin E have their own unique properties. For example, γ-tocopherol (also written as gamma-tocopherol) is a nucleophile that can react with electrophilic mutagens.^[5]

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]

So far, 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.

Compared with tocopherols, tocotrienols are poorly studied.^[14][15][16] Less than 1% of PubMed papers on vitamin E relate to tocotrienols.^[17] Current research direction are starting to give more prominence to the tocotrienols, the lesser known but more potent antioxidants in the vitamin E family. Tocotrienols have specialized roles in protecting neurons from damage^[18], cancer prevention^[19] and cholesterol reduction^[20] by inhibiting the activity of HMG-CoA reductase[16-1];δ-tocotrienol blocks processing of sterol regulatory element‐binding proteins (SREBPs)[16-1].

Oral consumption of tocotrienols is also proven to protect against stroke-associated brain damage in vivo. Disappointments with outcomes-based clinical studies testing the efficacy of α-tocopherol need to be handled with caution and prudence recognizing the untapped opportunities offered by the other forms of natural vitamin E.^[21] Toxicity studies of a specific form of tocopherol in excess should not be used to conclude that high-dosage “vitamin E” supplementation may increase all-cause mortality. Such conclusion incorrectly implies that tocotrienols are toxic as well under conditions where tocotrienols were not even considered.^[22] For more info, read article tocotrienol.

Contents 1 Food sources of Vitamin E 2 Vitamin E to prevent prostate cancer study discontinued 3 Congenital heart defects 4 References 5 Further reading 6 External links

[edit] Food sources of Vitamin E

Particularly high levels of vitamin E can be found in the following foods:^[23]

• Asparagus
• Avocado
• Egg
• Milk
• Nuts, such as almonds or hazelnuts
• Seeds
• Spinach and other green leafy vegetables
• Unheated vegetable oils
• Wheat germ
• Wholegrain foods

[edit] Vitamin E to prevent prostate cancer study discontinued

There have been some theories that Vitamin E, especially when coupled with selenium, may reduce the risk of prostate cancer^[24] by 30 percent.^[25] 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.^[26] 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. ^[24]

[edit] Congenital heart defects

A case control study done in the Netherlands using food frequency questionnaires found that high maternal Vitamin E by diet and supplements is associated with an increased risk of CHD (congenital heart defects) offspring, especially when the supplements are taken in the periconception period.^[27] (Note: case control studies are rated as low quality, grade 3 or 4, on a standard scale of medical evidence.^[28]) The National Health Service in the United Kingdom concludes that pregnant women should: "consider avoiding taking supplemental Vitamin E tablets."^[29]

[edit] References

[edit] Further reading

• Brigelius-Flohe, Regina (2002). "The European perspective on vitamin E: current knowledge and future research". American Journal of Clinical Nutrition 76 (4): 703. PMID 12324281. http://www.ajcn.org/cgi/pmidlookup?view=long&pmid=12324281. 

[edit] 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

v • d • e Vitamins (A11) Fat soluble A Retinol · β-Carotene · Tretinoin · α-Carotene D D2 (Ergosterol, Ergocalciferol)  · D3 (7-Dehydrocholesterol, Previtamin D3, Cholecalciferol, 25-hydroxycholecalciferol, Calcitriol (1,25-dihydroxycholecalciferol), Calcitroic acid) D4 (Dihydroergocalciferol)  · D5  · D analogues (Dihydrotachysterol, Calcipotriol, Tacalcitol, Paricalcitol) E Tocopherol (Alpha, Beta, Gamma, Delta) · Tocotrienol · Tocofersolan K Naphthoquinone · Phylloquinone/K1 · Menatetrenone/K2 · Menadione/K3 Water soluble B B1 (Thiamine) · B2 (Riboflavin) · B3 (Niacin, Nicotinamide) · B5 (Pantothenic acid, Dexpanthenol, Pantethine) · B6 (Pyridoxine, Pyridoxal phosphate, Pyridoxamine) B7 (Biotin) · B9 (Folic acid, Dihydrofolic acid, Folinic acid) · B12 (Cyanocobalamin, Hydroxocobalamin, Methylcobalamin, Cobamamide)  · Choline C Ascorbic acid  · Dehydroascorbic acid see also: enzyme cofactors, enzymes, Multivitamins