Institute of Medicine raises daily requirements for vitamins C and E

Scientists also set limits on maximum dosages

April 11, 2000
Web posted at: 1:44 p.m. EDT (1744 GMT)

In this story: Vitamin C Vitamin E Selenium Carotenoids RELATED STORIES, SITES

From staff and wire reports

WASHINGTON (CNN) -- The Institute of Medicine has raised the recommended daily requirements for two well-known antioxidants, vitamins C and E, and for the first time established maximum levels for those vitamins.

But the institute's latest report on Dietary Reference Intakes also said there was insufficient evidence to warrant taking high doses of antioxidants in the belief that they will prevent or cure ailments ranging from the common cold to cancer. A spokesman for the institute said "extremely large doses may lead to health problems rather than confer benefits."

The institute, a private, nonprofit organization that advises federal health officials, is part of the National Academy of Sciences, which has set the nation's Recommended Dietary Allowances, or RDAs, for nutrients since 1941. The Food and Drug Administration uses these recommendations to set "daily values" that appear on food labels.

Antioxidants are substances that cleanse the body of damaging oxygen molecules known as "free radicals," which are suspected of triggering diseases.

"Although a large number of population studies reveal a link between a diet rich in foods containing antioxidants, such as fruits and vegetables, and a lower incidence of certain chronic diseases, we cannot conclude at this time that the antioxidants are the reason," said Norman I. Krinsky, chair of the institute's antioxidant panel.

Other nutrients or factors could be causing the results, said Krinsky, a professor of biochemistry at Tufts University School of Medicine, Boston.

The report increases the daily levels for vitamins C and E, and for the first time sets upper limits for those vitamins and the nutrient selenium. Highlights from the report:

Recommended intake levels of vitamin C nutrient were increased to achieve maximum saturation in the body. Women should consume 75 milligrams per day, and men 90 milligrams. Because smokers are more likely to suffer from biological processes that damage cells and deplete vitamin C, they need an additional 35 milligrams per day. The old levels were 60 milligrams for adults.

The researchers said these levels can easily be met without taking supplements, and people can get vitamin C by eating citrus fruits, potatoes, strawberries, broccoli and leafy-green vegetables. An 8-ounce glass of orange juice provides about 100 milligrams of vitamin C. Any amount of the vitamin above the RDA is likely to be excreted by the body unused, Krinsky said.

The report sets the upper intake level for vitamin C, from both food and supplements, at 2,000 milligrams per day for adults. Intakes above this amount may cause diarrhea.

Vitamin E

The new recommended intake level of vitamin E for both women and men is 15 milligrams (22 International Units -- I.U.s). Food sources include nuts, seeds, liver and leafy-green vegetables. The vitamin E consumed shoud be "alpha-tocopherol," the only type that human blood can maintain and transfer to cells when needed. The old level was 8 milligrams for men and 6.4 milligrams for women.

The upper level, based only on intake from vitamin supplements, is 1,000 milligrams of alpha-tocopherol per day for adults, the scientists said. This amount is equivalent to roughly 1,500 I.U. of "d-alpha-tocopherol," sometimes labeled as "natural source" vitamin E, or 1,100 I.U. of "dl-alpha-tocopherol," a synthetic version of vitamin E.

People consuming more than the upper limit face a greater risk of stroke and uncontrolled bleeding because the nutrient can act as an anticoagulant.

The recommended intake level for selenium was set at the amount associated with the highest activity of enzymes that guard against oxidants in the body. Women and men should consume 55 micrograms per day, the report said. The old level was 70 micrograms for men, and 55 micrograms for women. Food sources include seafood, liver, meat and grains.

The report set the upper intake level for selenium at 400 micrograms per day. The level is based on nutrients from all sources. More than this amount could cause selenosis, a toxic reaction marked by hair loss and brittle nails.

The report noted that most American and Canadian adults already get sufficient quantities of these three nutrients from their food.

In laboratory tests, Beta-carotene and other carotenoids have been shown to act as antioxidants, but the results have not been consistently duplicated in humans, the report said. In addition, data on the adverse effects of carotenoid overconsumption are contradictory.

For these reasons, the scientists did not recommend a daily intake level or an upper intake level for consumption of carotenoids. People should use caution before taking them in high doses; the report recommended beta-carotene supplementation only for the prevention and control of vitamin A deficiency.

Healthy people should not routinely exceed upper intake levels, the scientists recommended.

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