Vitamin E is a fat soluble vitamin which serves as an antioxidant, and also plays a role in immune function and metabolism. It is readily available from nuts, seeds, and vegetable oils, as well as dark green vegetables such as broccoli and spinach.
Though most Americans consume adequate amounts of vitamin E through diet, supplements are widely available, often with doses somewhat higher than the recommended daily allowance. This is most likely because consumers believe that vitamin E may protect them against cancer, heart disease, and diseases of aging such as Alzheimer's. There is little or conflicting evidence of these claims, however, so taking these supplements may be a waste of money and effort, though there is no convincing evidence that high doses of vitamin E are dangerous.
Vitamin E and Heart Disease
The theory is that vitamin E may prevent heart disease or cardiac events in two ways. First, vitamin E is thought to reduce thickening of the artery walls by slowing the rates of oxidation of low density lipoprotein (LDL) cholesterol. Second, vitamin E may help to prevent the formation of blood clots which might result in a heart attack.
However, actual clinical trials of people at risk for heart attack or stroke have shown that taking vitamin E does not reduce mortality or the risk of non-fatal heart attack and in some cases, death rates (not necessarily from heart attack or stroke) were actually higher in the groups taking the supplements. The participants in these studies have typically been at-risk for heart disease and stroke; it is possible that vitamin E may protect those who are young and healthy from developing disease, but no evidence is yet available that this is the case.
Vitamin E and Cancer
Because vitamin E is an antioxidant, some theorize that it may prevent free radicals from damaging cells and causing cancer. It is also possible that it could prevent nitrates in foods from becoming carcinogens in the stomach, or even protect against cancer by simply boosting immune function.
As with heart disease, however, clinical trials comparing long-term health outcomes of those taking supplements and those not taking supplements are inconsistent. Some studies suggest that vitamin E reduces the incidence of cancer, while others found no difference.
Vitamin E and Aging
Vitamin E is thought to prevent or slow some of the degenerative diseases of aging, such as Alzheimer's, because it is an antioxidant. If free radical damage to the brain cells is one of the causes of cognitive decline in later years, then anything that slows their action would help to maintain health in old age. However, clinical trials with both healthy and mildly impaired individuals showed no difference between those taking vitamin E supplements and those taking a placebo.