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]
Contents |
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 information, 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[17], cancer prevention[18] and cholesterol reduction[19] 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.[20] 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.[21] For more info, read article tocotrienol.
Particularly high levels of vitamin E can be found in the following foods:[22]
Brackets contain the amount and proportion of the daily allowance of vitamin E.
There have been some theories that Vitamin E, especially when coupled with selenium, may reduce the risk of prostate cancer[23] by 30 percent.[24] 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.[25] 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.[23]
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.[26] (Note: case control studies are rated as low quality, grade 3 or 4, on a standard scale of medical evidence.[27]) The National Health Service in the United Kingdom concludes that pregnant women should: "consider avoiding taking supplemental Vitamin E tablets."[28]
A Finnish study found that Vitamin E supplementation increased the risk of hemorrhagic stroke (The Alpha-Tocopherol Beta-Carotene Cancer Prevention Study Group. The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. N Engl J Med 1994;330:1029–35.) Vitamin E supplementation was shown to increase the risk of heart failure in a 2005 study published in the Journal of the American Medical Association by Lonn, et al., which studied 7,000 people (JAMA. 2005 Mar 16;293(11):1338-47. Effects of long-term vitamin E supplementation on cardiovascular events and cancer: a randomized controlled trial.)
Urologists commonly recommend Vitamin E supplementation as a treatment for Peyronie's disease. Some success has been reported in older trials, but those successes have not been reliably repeated in larger, newer studies.[29]
Vitamin E deficiency causes neurological problems due to poor nerve conduction. These include neuromuscular problems such as spinocerebellar ataxia and myopathies.[30] Deficiency can also cause anemia, due to oxidative damage to red blood cells.
|
||||||||||||||||||||||||||||||
Vitamin E (which is also called Tocopherol or Tocotrienol, E307, E308,E309) is a vitamin. There are eight forms of it, E1 to E8. It can be found in vegetable oils. Very often it is also added to lotions and creams for the skin. It is supposed to help the healing of the skin, after burns and injuries, and lower the risk of heart disease and cancer.[1]
Vitamin E is claimed to help Anti-Aging.[needs proof]
   | Vitamin E - MedlinePlus Medical Encyclopedia: Vitamin E |
| | Vitamin E - Vitamin E Fact Sheet |
| | The European perspective on vitamin E: current knowledge and future research - The European perspective on vitamin E: current knowledge and future research -- Brigelius-Flohé et al. 76 (4): 703 -- American Journal of Clinical Nutrition |
| | Vitamins E and C in the Prevention of Cardiovascular Disease in Men: The Physicians' Health Study II Randomized Controlled Trial - JAMA -- Vitamins E and C in the Prevention of Cardiovascular Disease in Men: The Physicians' Health Study II Randomized Controlled Trial, November 12, 2008, Sesso et al. 300 (18): 2123, Data Supplement - JAMA Report Video |
| | ''The SELECT Prostate Cancer Prevention Trial'' - The SELECT Prostate Cancer Prevention Trial - National Cancer Institute |
| | ''Selenium and Vitamin E Cancer Prevention Trial (SELECT)'' - Selenium and Vitamin E Cancer Prevention Trial (SELECT) - National Cancer Institute |
|
|
Wikis
Quiz
Map
Search
