Vitamin E is a fat-soluble substance made up of 8 chemically distinct compounds. Of these, alpha-tocopherol is an antioxidant, which is necessary to keep cell membranes healthy, and may defend cell components against the effects of oxidative stress. Its health-promoting effects depend on its demonstrated functions such as:
- prevention of oxidative damage
- protection of lipids in cell membranes
- regulation of platelet aggregation and inflammatory prostaglandin production
The health benefits of vitamin E have been studied with reference to four areas:
Coronary heart disease
Research has shown that vitamin E prevents the oxidation of LDL cholesterol which is thought to be the first step in the formation of an atherosclerotic plaque. It also inhibits platelet clot formation which precipitates the production of a coronary thrombus.
Several observational studies found an inverse correlation between heart disease and vitamin E intake from food or from supplementation. However, randomized clinical trials like the Heart Outcomes Prevention Evaluation, or HOPE study, did not confirm this finding.
There was no reduction in the incidence of clinical coronary events in people over 50 years who had heart disease or diabetes, with moderately high doses of vitamin E. A follow-up study on the same patients (HOPE-TOO) found no evidence of the efficacy of vitamin E in preventing cardiovascular disease either.
Another large trial confirmed that there was no overall drop in mortality from all causes, but in women above 65, the number of nonfatal myocardial infarctions went down by more than a quarter, while the cardiovascular mortality decreased by almost 50%. Considering all women, it was reduced by 24%.
This has not been confirmed in men, however, and a worrisome finding was the increased incidence of hemorrhagic stroke with vitamin E supplementation. Additional trials are needed to understand the possible preventive role of vitamin E in younger, healthy people, as most trials have focused on the older group of patients with established risk factors for heart disease.
The antioxidant action of vitamin E has been thought to bring about a preventive effect on cancer development by blocking cell damage due to free radical action. A few large studies showed a reduction in prostate cancer with vitamin E supplementation, but the SELECT study showed no such benefit, and its follow up revealed a statistically significant increase in prostate cancer among men who had taken vitamin E earlier.
Similar claims of benefits in reducing the incidence of colon and bladder cancer remain to be confirmed. However, it is noteworthy that some researchers found that gamma-tocopherol had a cancer-preventive effect which pure alpha-tocopherol lacked, by inactivating the cancer-promoting Akt gene.
Significant vision loss is due to age-related macular degeneration and cataracts in most older people. Since they are postulated to arise from the cumulative damage caused by oxidizing free radicals, vitamin E supplementation was thought to be of benefit.
However, this has not been proved to be the case. Disease progression, in the case of AMD, has been slowed down by about 25% with a supplement containing multiple antioxidants.
The brain consumes a lot of oxygen as well as having many fatty acids in its neuronal membranes. The progression of brain damage in Alzheimer’s disease is due to a mechanism that involves the production of hydrogen peroxide in the presence of the beta-amyloid protein that is the hallmark of this disease process in the brain.
Vitamin E prevents this oxidation, and in high doses was found to delay the time of institutionalization and functional deterioration in elderly patients with moderate degrees of Alzheimer’s disease, though they had more falls. In healthy people, however, it does not appear to slow cognitive decline.
Other applications of vitamin E
High doses of vitamin E have been found by some researchers to restore cellular immune function and stimulate CD4 proliferation. The risk of disease progression was significantly less with high levels of vitamin E in the blood.
Immune function in rats returned to normal with a dietary level of vitamin E that was 15 times normal. It also protected against bone marrow depression in rats induced by chemotherapy drugs such as azidothymidine. However, higher mortality has also been reported, making further study necessary.
The effect of vitamin E supplementation over long periods has been found helpful in diabetes mellitus, by reducing HbA1C and fasting insulin levels, suggesting lower glucose concentrations in blood.
This also improved endothelial function in diabetics with normal weight or overweight, but not in obese diabetics. However, other studies have shown no reduction in the risk of vascular complications or mortality from diabetes, or in the incidence of diabetes.
A few trials also found improvement in disease activity when vitamin E was administered to patients with non-alcoholic fatty liver disease, as well as lowering of serum disease markers such as aminotransferase activity, improvement in insulin sensitivity and the serum lipid profile, but more confirmation is required to make recommendations.