Panel ups RDAs for some antioxidants

Dietary antioxidants such as vitamins C and E can limit cellular damage from free radicals, which are damaging molecular fragments produced by the body. However, warns Norman I. Krinsky of Tufts University School of Medicine in Boston, studies in people have never “adequately” established a direct connection between antioxidant consumption and prevention of chronic disease. Overconsumption may even prove harmful.

Krinsky offered these take-home messages from a new report on the body’s need for antioxidants. He chaired a panel that prepared the 485-page assessment published this week by the Institute of Medicine (IOM) in  Washington, D.C.

Over the past few years, the institute has periodically recruited experts to set or revise recommended daily allowances (RDAs) for various nutrients. At the same time, it’s begun expanding those dietary guidelines to include, among other things, a “tolerable upper intake”—a ceiling on how much of a given nutrient individuals can safely consume. Such ceilings, the new report emphasizes, shouldn’t be confused with RDAs.

For nonsmokers, the RDA for vitamin C, issued 11 years ago, was 60 milligrams for adults and 70 mg for pregnant women. Krinsky’s committee has now increased those values slightly—to 75 mg for women, whether pregnant or not, and 90 mg for men.

Since 1989, the institute has recommended that smokers consume 40 mg/day more of this antioxidant to help counter the oxidative stress posed by cigarette smoke. In the new report, Krinsky’s team recommends for smokers a 35-mg daily increase above the new RDAs. The team also sets the ceiling on safe vitamin C intake at 2,000 mg/day.

The new report more than doubles the RDA for vitamin E—which occurs naturally as RRR-alpha-tocopherol—to 15 mg, or 22 international units (IU), for adults. Krinsky’s group also set a tolerable upper intake at 1,500 IU of this form of the vitamin.

The new adult RDA for selenium is 55 micrograms (µg). That represents no change for women but a decrease of 20 µg/day for men. The institute has set an upper intake limit of 400 µg/day. Finally, as in previous IOM reports, the team found the available data insufficient for deriving RDAs for beta-carotene and other carotenoids.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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