WASHINGTONScientific studies provide insufficient evidence that consuming high doses of antioxidants in the diet and as supplements can prevent chronic diseases, according to a new report by the Institute of Medicine (IOM), a part of the National Academy of Sci-ences. Indeed, megadoses of some antioxidants may lead to ill health rather than benefits, the report warned.
Dietary Reference Intakes
In its latest Dietary Reference Intakes report, an IOM committee addressed the use of vitamins C and E, selenium(Drug information on selenium), and carotenoids as ways to prevent such ailments as cancer, cardiovascular disease, eye diseases, and neurodegenerative diseases, including Alzheimers and Parkinsons disease.
A direct connection between the intake of antioxidants and the prevention of chronic disease has yet to be adequately established, said committee chair Norman I. Krinsky, PhD, professor of biochemistry, Tufts University School of Medicine. We do know, however, that dietary antioxidants can, in some cases, prevent or counteract cell damage that stems from exposure to oxidants. But much more research is needed to determine whether dietary antioxidants can actually stave off chronic disease.
In addition to recommending minimum daily requirements for three of the substances, the report also set a maximum dosage as a way of avoiding adverse effects:
Vitamin C: A minimum dose of 75 mg for women and 90 mg for men, plus an additional 35 mg for those who smoke. The maximum daily amount should be 2,000 mg.
Vitamin E: Men and women should both consume a minimum of 15 mg, or 22 International Units (IU), of alpha-tocopherol from food daily, the only form of vitamin E(Drug information on vitamin e) that can enter cells.
The maximum from supplements should be 1,000 mg/d of alpha-tocopherol, which is equal to 1,500 IU of d-alpha-tocopherol, sometimes labeled as a natural source of vitamin E, or 1,100 IU of dl-alpha-tocopherol, a synthetic version of vitamin E.
Selenium: Women and men should both get at least 55 µg/d and a maximum of 400 µg/d.
Carotenoids: Because laboratory tests have failed to show conclusively that carotenoids, including beta-carotene, act as antioxidants, the committee did not recommend either a minimum or maximum daily dose.