The main function of vitamin E (alpha-tocopherol) in humans appears to be that of an antioxidant. The fat-soluble vitamin is uniquely suited to intercepting the damaging effects of oxidation by free radicals and thus preventing lipid destruction in cell membranes.
Vitamin E (alpha-tocopherol) also protects the fats in low density lipoproteins (LDLs) ─ particles that transport cholesterol from the liver to the tissues of the body ─ from oxidation. Oxidized LDLs have been implicated in the development of cardiovascular diseases (see Disease Prevention) (3, 4).
Alpha-tocopherol is also known to inhibit the activity of the important cell-signaling molecule ‘protein kinase C’.
In addition, vitamin E appears to affect the production and activities of molecules and enzymes in immune and inflammatory cells, it has been shown to inhibit blood clotting (‘platelet aggregation’), and is seems to enhance relaxation or opening of blood vessels (‘vasodilation’) (2, 5).
The European Food Safety Authority (EFSA), which provides scientific advice to assist policy makers, has confirmed that clear health benefits have been established for the dietary intake of vitamin E in contributing to:
The function of the vitamin E form ‘gamma-tocopherol’ in humans is presently unclear. Blood levels of gamma-tocopherol are generally ten times lower than those of alpha-tocopherol because only the alpha form is preferentially incorporated for transportation into lipoproteins (1), while other forms of vitamin E are actively metabolized (6). For this reason, the Food and Nutrition Board decided that alpha-tocopherol, but none of the other naturally occurring forms of vitamin E (beta-, gamma-, and delta-tocopherols and the tocotrienols), contributes to meeting vitamin E requirements (2). Nonetheless, gamma-tocopherol has been described to have biological activity.
Limited research in vivo and in animals indicates that gamma-tocopherol may play a role as antioxidant in protecting the body from free radical-induced damage (7, 8), but these effects have not been convincingly demonstrated in humans.
In one prospective study, increased levels of blood gamma-tocopherol were associated with a significantly reduced risk of developing prostate cancer. In this study, increased levels of blood alpha-tocopherol and toenail selenium were protective against prostate cancer development only when gamma-tocopherol levels were also high (9). These limited findings, in addition to the fact that alpha-tocopherol supplementation lowers gamma-tocopherol levels in blood, have led some scientists to call for additional research on the effects of dietary and supplemental gamma-tocopherol on health (10).
Authored by Dr Peter Engel in 2010, reviewed and updated by Dr Szabolcs Peter on 18.06.2017
