There is no convincing scientific evidence that taking large amounts of vitamin C, vitamin E, or the nutrients selenium and beta carotene can reduce the chances of getting cancer, heart disease, diabetes, Alzheimer's disease or other illnesses, a National Academy of Sciences panel announced Monday.
Despite popular belief that high doses of these so-called antioxidants can protect the body from a variety of illnesses, including the common cold, there is insufficient evidence to recommend that Americans get more of these nutrients than is necessary to prevent basic nutritional deficiencies, the panel said. In fact, extremely high doses might lead to health problems, according to the panel, which for the first time set upper limits for vitamins C and E and for the mineral selenium.
The panel, which is revising all the government's official recommendations for how much vitamins and minerals Americans should get every day, also found insufficient evidence to set a minimum intake level for beta carotene, one of the most popular antioxidant supplements, or for lutein or lycopene. And because of evidence that beta carotene can potentially cause cancer in some people, especially smokers, the panel urged caution before taking it in high doses, recommending supplements "only for the prevention and control of vitamin A deficiency."
That finding alone could have enormous impact on the booming multivitamin industry, according to nutrition experts. Beta carotene and vitamin A together accounted for an estimated $230 million of the $5.7 billion vitamins sold in 1999. More than 300 types of multivitamins sold just in natural food stores contain beta carotene in some form, according to one estimate.
Because the recommendations will be used to update other federal nutritional guidelines, they are expected to have wide-ranging effects, including on school lunches, food programs for low-income families and the content of nutrition labels on foods and on vitamin and mineral supplements.
"This report underscores the importance of getting your nutrients from food versus pills," said Janet Helm, a spokeswoman for the American Dietetic Assn.
Antioxidants are vitamins and minerals that can help neutralize so-called free radicals--oxygen and nitrogen molecules with unpaired electrons--that have been linked to illnesses, including cancer, cataracts, heart disease and strokes.
The report, which is the third in an ongoing series of dietary recommendations for Americans and Canadians, follows an exhaustive two-year review of all the existing medical literature about antioxidants.