WASHINGTON -- While Americans should have more vitamins C and E in their diets than currently recommended, huge doses of these vitamins and other antioxidants have no proven benefit and may even be harmful, government researchers said Monday.
Antioxidants scavenge the body for roaming oxygen molecules known as ''free radicals'' suspected of triggering cancer and other disease. Many people routinely take high doses of vitamin C and other antioxidants in the belief that they will prevent or cure illnesses.
But not enough evidence exists to support claims that massive doses of antioxidants can improve health, said researchers from the Institute of Medicine. The institute, a private organization that advises the federal government, is reviewing the nation's Recommended Daily Allowances, or RDAs, for nutrients.
''Much more research is needed to determine whether dietary antioxidants can actually stave off chronic disease, '' said Norman I. Krinsky, chair of the study's antioxidant panel.
For the first time the institute has set upper limits on the daily consumption of vitamins C and E to reduce the risk of harmful side effects.
Adults should keep their daily vitamin C intake from both food and supplements below 2,000 milligrams because anything higher may cause diarrhea.
The upper level for vitamin E, based only on vitamin supplements, is 1,000 milligrams. That's roughly equivalent to 1,500 International Units, or I.U., of ''d-alpha-tocopherol,'' sometimes labeled as ''natural source'' vitamin E. Since the nutrient can act as a blood anticoagulant, people consuming more than the upper limit face a greater risk of uncontrolled bleeding.
Although most American and Canadian adults already get enough of their vitamins C and E in their food, the researchers decided to increase the current overall intake recommendations.
Under the new recommendations, women should consume 75 milligrams of vitamin C each day, and men should consume 90 milligrams. Smokers, who are more likely to suffer from damaged cells and depleted vitamin C levels, need an additional 35 milligrams daily.
People can get vitamin C by eating citrus fruits, potatoes, strawberries, broccoli, and leafy green vegetables.
For vitamin E, both women and men should consume 15 milligrams or 22 I.U. each day from food sources including nuts, seeds and liver. The vitamin E consumed should be ''alpha-tocopherol,'' the only type that human blood can maintain and transfer to cells when needed.
Women and men should also get 55 micrograms of the nutrient selenium each day from foods including seafood, liver, meat, and grains, according to the recommendation.
The maximum intake level for selenium from both food and supplements is 400 micrograms per day. More than this amount could cause selenosis, a toxic reaction marked by hair loss and brittle nails.
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