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Role of antioxidants in disease prevention is uncertain
IOM report sets ceiling on daily consumption of selenium, vitamins C and E.
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WASHINGTON — Insufficient evidence exists to support claims that taking megadoses of dietary antioxidants, such as selenium and vitamins C and E, or carotenoids, including beta-carotene, can prevent chronic diseases, according to the latest report on dietary reference intakes from the Institute of Medicine (IOM) of the National Academies of Sciences. Extremely large doses may lead to health problems rather than confer benefits.
“A direct connection between the intake of antioxidants and the prevention of chronic disease has yet to be adequately established,” said Norman I. Krinsky, PhD, chair of the study’s Panel on Dietary Antioxidants and Related Compounds, and 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, which are agents that affect a cell’s molecular composition. But much more research is needed to determine whether dietary antioxidants can actually stave off chronic disease,” Dr. Krinsky said.
The report, the third in a series on dietary recommendations for healthy Americans and Canadians, calls for increases in daily intakes of vitamins C and E to exploit their role in maintaining good health and recommends an even larger amount of vitamin C for smokers.
New dietary recommendations
Vitamin C. Women should consume 75 mg/day and men 90 mg/day. Smokers need an additional 35 mg/day. Upper intake level for vitamin C, from both food and supplements, is set at 2,000 mg/day for adults. Intakes above this amount can cause diarrhea. Food sources are citrus fruit, potatoes, strawberries, broccoli and leafy green vegetables.
Vitamin E. Both women and men should consume 15 mg (22 IU) of alpha-tocopherol from food sources each day (nuts, seeds, liver, leafy green vegetables). Upper intake level recommended from vitamin supplements is 1,000 mg of alpha-tocopherol/day (roughly equivalent to 1,500 IU of d-alpha-tocopherol, sometimes labeled as natural source vitamin E, or 1,100 IU of dl-alpha-tocopherol, a synthetic version of vitamin E). Intakes above that amount can impose risk of hemorrhagic damage because the nutrient can act as an anticoagulant.
Selenium. Recommended intake is 55 µg/day. Food sources are seafood, liver, meat and grains. Upper intake level is 400 µg/day, based on nutrients from all sources. Higher intake can cause selenosis, a toxic reaction marked by hair loss and nail sloughing.
Beta-carotene and other carotenoids. Report does 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. Beta-carotene supplementation is recommended only for the prevention and control of vitamin A deficiency.
Do not exceed upper intake levels
The report advises that healthy people should not routinely exceed upper intake levels. How nutrient consumption above these levels may affect human health should be studied further in well-controlled clinical trials.
Likewise, much more research is needed to investigate the role of dietary antioxidants and carotenoids in the prevention of chronic disease; to explore the nutrient needs of specific groups of people, including children and the elderly; and to look into how selenium, vitamins C and E, and beta-carotene interact with each other and with other food components.
Editor’s note:This article originally appeared in Cardiology Today, a SLACK, Incorporated publication.
For Your Information:
- Dietary reference intakes for vitamin C, vitamin E, selenium and carotenoids are available from the National Academy Press, (202) 334-3313 or (800) 624-6242.