April 11, 2000 (Washington) -- If you're taking large doses of vitamins C and E or other antioxidant supplements like selenium or carotenoids to ward off chronic diseases, you may be doing yourself more harm than good. That's the major conclusion of a new report from the Institute of Medicine (IOM), a division of the National Academy of Sciences.
In its analysis, titled "Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids," the IOM's expert panel looked at the controversial question of whether taking these antioxidants could help prevent conditions like cardiovascular disease, Alzheimer's disease, or certain types of cancer. It is believed that antioxidants interfere with certain forms of oxygen and nitrogen in the blood called free radicals that can damage normal cells.
However, after a review of the available studies, the panel concluded that, at least for now, there's not enough evidence about the benefits of antioxidants to say they prevent disease, even though many suggest that eating foods rich in these substances lowers the risk of illness.
"What is known, however, is that taking very large quantities of some antioxidants can actually cause health problems," said panel chair Norman Krinsky, PhD, at a news conference Tuesday.
Krinsky, a biochemist at the Tufts University School of Medicine, says the panel's recommendation is to consume either the recommended daily allowance (RDA) or no more than what is considered the maximum safe amount, or "tolerable upper intake level." Anything in that range should be safe, according to the IOM.
The panel says too much vitamin C can cause diarrhea, excess amounts of vitamin E have been linked to bleeding, and selenium in megadoses is known to trigger hair loss as well as cause brittle fingernails and toenails. These side effects are increasingly a cause for concern as more Americans choose to manage their health care by taking supplements.
You do have some reason to be interested in antioxidants, however. Some studies show that vitamin E may slow the rate of mental decline in the early phases of Alzheimer's disease. Vitamin C may not prevent the common cold, but research indicates it shortens the duration of symptoms.
However, food should be a sufficient source of antioxidants, says the report. Those who take supplements may wonder whether certain types or forms are preferable. "It doesn't have any impact on the upper limit, but if you are going to take a supplement, it really should be taken with a meal [to be better absorbed]," says panelist Maret Traber, PhD, a nutritionist at Oregon State University.
For vitamin C, the daily recommendation is 75 mg for women and 90 mg for men. These numbers actually represent a 50% increase for men and a 25% jump for women. Smokers should get another 35 mg of C daily, as the antioxidant may counter the damage smoking does to cells, according to the report. The suggested upper limit, however, is 2,000 mg daily of vitamin C for adults. Fruits and vegetables are a good source of C.
With vitamin E, the guidance is 15 mg of the substance daily, and it can be most efficiently obtained from foods containing alpha-tocopherol such as nuts, seeds, liver, and leafy green vegetables. This is a 100% increase over the previous level. The suggested upper limit for vitamin E is 1,000 mg per day.
The recommendation for selenium is 55 micrograms per day in foods like seafood or liver. The safe upper limit is 400 micrograms daily. Suggested levels for beta-carotenes and carotenoids, found in many plants, weren't included in the report, because the authors say there's doubt the nutrients actually are antioxidants.
Doubts or not, many people are taking supplements, and not necessarily with their doctor's knowledge or advice -- even for serious conditions like heart disease. Many are taking "huge doses of vitamin E," says Ernst Schaefer, MD, a professor of medicine and nutrition at New England Medical Center and Tufts University.
"All I can do to my patients is to say, 'Look, I'm data driven. I'm not saying that these things don't help you, but in fact we have to be guided by [research],'" Schaefer tells WebMD.
The IOM report also focuses on the need for more research to determine whether antioxidants really work. Meanwhile, the report is being generally well received.
"I think it will raise people's awareness of how much [in the way of nutrients] they're consuming. ... It's sort of a check to yourself," says Edie Hogan, RD, spokesperson for the American Dietetic Association.