March 18, 2011
Dear Mayo Clinic:
Are there any risks to taking vitamin E daily?
Research has shown possible risks to taking vitamin E. Because of those risks, and because vitamin E supplements have not been shown to offer significant health benefits, I do not recommend taking vitamin E supplements for disease prevention.
Vitamin E is found in vegetable, nut and seed oils. Foods that contain vitamin E include canola oil, olive oil, margarine, almonds and peanuts. A main function of vitamin E in the body is as an antioxidant.
Antioxidants neutralize unstable molecules called free radicals. Free radicals may contribute to aging and chronic diseases by damaging (oxidizing) other molecules. Regarding cholesterol and heart disease, studies have shown that when low-density lipoprotein (LDL) cholesterol is oxidized by free radicals, it is more likely to contribute to the buildup of fatty deposits (plaques) in the arteries, which can lead to a heart attack or stroke.
Because it's an antioxidant, researchers wanted to find out if taking a vitamin E supplement could improve heart health. In the early 1990s, laboratory research showed that, in test tubes, vitamin E prevented the oxidation of LDL cholesterol. Vitamin E also showed benefits on heart health in animals. When researchers conducted population studies in humans, they found that people who took the most vitamin E had the lowest risk of heart disease.
These findings created excitement about possible benefits of taking vitamin E. However, when researchers began conducting carefully controlled clinical trials that compared people who took vitamin E supplements with those who didn't, the findings were different. In 2001, Mayo Clinic researchers published a review article that indicated there were three large clinical trials up to that time involving more than 25,000 patients — and vitamin E didn't show much benefit.
Then, in 2005, results from two important research studies were published. The first was a long-term study of people taking vitamin E supplements. It found that not only was there little or no benefit from taking vitamin E, it also revealed that people who took vitamin E supplements had an increased risk of heart failure. The second study was a review of findings from 67 clinical trials involving vitamin E and other antioxidant supplements. (This type of research, that reviews previous studies and evaluates their results together, is called a meta-analysis.) It found an increased risk of death in people who took vitamin E. Since 2005, there has been no new evidence to contradict these findings.
Why vitamin E doesn't provide health benefits in supplement form isn't clear. It may be because vitamin E isn't just one substance. There are two sets of vitamin E compounds, and a variety of subsets within those. Most supplements are made of only one type of vitamin E. It might be that, isolated from the other vitamin E compounds, one type of vitamin E doesn't work the same way in the body as it does when combined with the others, as it is in foods.
The amount of vitamin E in supplements also may be a factor. In the United States, the median daily intake of vitamin E from food is about 5 to 10 milligrams (mg). Vitamin E supplements generally contain 268 or 537 mg (400 or 800 international units). Taking vitamin E in quantities that much higher than normal may have an adverse effect on the body. Multivitamins contain vitamin E in amounts much closer to the Recommended Dietary Allowance of 15 mg/day for adults, so they aren't a problem.
The bottom line is that even though initial laboratory studies, animal studies and population research into the health benefits of vitamin E looked promising, the clinical trial findings — which provide the best form of evidence — didn't bear that out. Instead, they uncovered health risks that make it unwise to take separate vitamin E supplements.
— Donald Hensrud, M.D., Endocrinology, Mayo Clinic, Rochester, Minn.