IOM report warns of high vitamin levels

New Institute of Medicine recommendations say that even common vitamin supplements like C, E and selenium can do harm if not used properly.

By Stephanie Stapleton, amednews staff. May 1, 2000.

Washington -- Rarely a week passes without news reports about the protective powers of antioxidants -- vitamin C, vitamin E, selenium and beta-carotene. And doctors are increasingly aware that their patients are paying attention.

But an April 11 Institute of Medicine report offered words of caution and guidance for both the physician and the consumer in pursuing this course of prevention.

The IOM warned against the daily use of megadoses of these nutrients because too much could cause harmful side effects. The IOM also updated daily recommended allowances and set upper intake levels. In addition, the panel noted that it is important for physicians to be aware of their patients' vitamin use.

"I believe it would be very useful for a physician to know what level of vitamin supplements a patient is taking and to caution them if they feel they are taking levels above the upper levels," said Norman I. Krinsky, MD, chair of the IOM panel on dietary antioxidants and related compounds and a professor at Tufts University School of Medicine in Boston.

New guidelines

Dietary antioxidants are nutrients that help protect cells from oxidative stress. For years, researchers have sought to pinpoint how these nutrients may function to reduce the risk of a variety of illnesses. But questions still remain, and the IOM called for more research to provide definitive answers.

"A direct connection between the intake of antioxidants and the prevention of chronic disease has yet to be adequately established," said Dr. Krinsky. Right now, there is insufficient evidence to conclude that such nutrients, even in very high doses, will reduce the risk of diseases such as cancer, cardiovascular disease, cataracts and age-related macular degeneration. For example, though vitamin E "has shown some promise" in regard to Alzheimer's, larger studies that will provide more information are still in progress, said Ishwarlal Jialal, MD, PhD, a panel member from the University of Texas Southwestern Medical Center in Dallas.

But the panel also was clear that its intent was not to prevent their use.

"It is not that there is no evidence," said Maret G. Traber, PhD, a panel member from Oregon State University in Corvallis. "There is no unequivocal proof."

What the IOM did was set daily levels appropriate for "the normal, average, healthy person," she said. "If [a person] is under the care of a physician, the amount can be higher." As long as it is within the upper limit, it is a personal decision, Dr. Traber added.

That decision, though, should not be made without the consideration of other variables. For instance, if a patient has hemochromatosis, high doses of vitamin C -- which enhances iron absorption -- could be problematic. Physicians also should factor in a patient's diet.

"Our concern would be that physicians not recommend doses that in combination with foods would exceed upper intake levels," Dr. Krinsky said. "At doses below that, a physician may in fact feel there is a benefit."

To that end, the IOM panel updated daily recommended allowances and, for the first time ever, set a ceiling on daily consumption. For vitamin C, it called for 75 mg per day for women and 90 mg per day for men. Smokers should add 35 mg more daily. But no one should exceed 2,000 mg. More may cause symptoms such as diarrhea.

The daily recommended intake for vitamin E is 15 mg from food or 22 international units from a natural-source vitamin E supplement. Intake that exceeds 1,000 mg could cause hemorrhagic disorders.

For selenium, the panel recommended 55 micrograms per day and no more than 400 micrograms. Higher doses could cause hair loss and nail brittleness.

The panel opted not to address beta-carotene because laboratory findings supporting its antioxidant power have not been consistently duplicated in human studies.