BioEd Online

Stocking up on vitamin E pills may damage more than the contents of your wallet. The dose of vitamin E contained in off-the-shelf supplements can increase your risk of dying, if taken daily, researchers have found.

The large market in vitamin supplements relies on the popular assumption that raising vitamin levels has health benefits. But the precise effect that high doses of vitamins have on the human body is not well documented, and is subject to much debate.

Researchers from the United States, Spain, and Britain analysed the results of many different clinical trials to assess the overall value of vitamin E. To their surprise, they found that individuals taking daily doses of 400 international units (IU), the amount of vitamin E in common off-the-shelf supplements, were 10% more likely to die than they would have been if they had not taken the supplement at all.

"Companies make all sorts of nebulous claims about vitamin E having certain health benefits. But that's not based on science, that's just marketing," says Edgar Miller, an epidemiologist at Johns Hopkins University, Baltimore, and lead author of the study, which is being published in the Annals of Internal Medicine¹.

Vital vitamin

Vitamin E contains a powerful antioxidant that is thought to protect cells and tissues from damage by neutralizing free radicals. It is also believed to aid wound healing, boost the immune system, and promote healthy circulation.

The vitamin is found naturally in vegetable oils, leafy vegetables, and nuts. It is soluble in fat rather than water, meaning that excess levels can accumulate in the body's tissues.

Nutrition experts recommend that a balanced daily diet should contain around 10-20 milligrams (or 15-30 IU) of vitamin E. But its antioxidant properties have prompted speculation that higher doses could protect against cardiovascular disease and cancer. Individual investigations designed to test this theory have yielded conflicting results.

Danger in excess

Miller's study was presented today at a meeting of the American Heart Association in New Orleans. The researchers pooled data from 19 different trials, which together involved over 130,000 participants.

Vitamin E doses used in the trials ranged from just 16.5 IU up to 2,000 IU, which is double the limit that US dietary guidelines regard as tolerable. On pooling the results, the researchers found that daily doses of 150 IU or less had no adverse effects, and might even offer health benefits. Risk of death started to increase above this level, and became significant at 400 IU and higher.

"Data to support the benefit of these high doses is really nonexistent," says David Waters, professor of medicine at the University of California San Francisco, and a cardiologist at San Francisco General Hospital. "When you call something a 'vitamin', people assume it is beneficial. No one dreams that it could be harmful. But there is no reason why, like any other chemical compound, it shouldn't be harmful when taken above a certain limit."

The study's authors recommend that people should stop taking any high dose vitamin supplements until further clinical trials demonstrate their worth, or at least rule out harm. Vitamins A and D are fat-soluble like vitamin E, and will similarly accumulate in the body's tissues.

Vitamin C is an antioxidant like vitamin E, but because it is water-soluble, it is unlikely to build up in the body to the same extent. But some people take high doses of vitamins C and E together and the effect of this combination is unknown, Miller says: "The jury is still out on vitamin C."