Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
6/27/00
Contacts:
Elisabeth Schafer, ISU Extension Food Science and Human
Nutrition, (515) 294-1359, eschafer@iastate.edu
Diane Nelson, ISU Extension Communication Systems, (515),
294-3178, dinelson@iastate.edu
New Dietary Recommendations for Antioxidant Vitamins and Minerals
AMES, Iowa - The National Academy of Sciences recommends that Americans get a bit more vitamin C and vitamin E than previously was thought necessary for health. "The increased recommendations are small but significant," said Elisabeth Schafer, extension nutritionist at Iowa State University. "And, for the first time, the Academy also set an upper level. The report found too little evidence to support claims for taking megadoses to prevent chronic diseases. In fact, extremely large doses of selenium and vitamins C and E or carotenoids like beta-carotene could cause health problems rather than prevent them."
Interest in antioxidants has grown as researchers have identified their role in helping to protect cells from a normal, but damaging, physiological process known as "oxidative stress." Oxygen is essential to life, and all cells use oxygen. However, oxygen also can be harmful if it forms free radicals that damage the cell. "One purpose of the antioxidant nutrients is to allow cells to get the benefit of the oxygen without also being harmed in the process," Schafer said. "Many foods, especially fruits and vegetables, are natural sources of antioxidants. This is one reason nutritionists emphasize eating more fruits and vegetables daily. Antioxidants also have been added to some foods and are available in the form of dietary supplements."
"We recommend that everyone--children and adults--eat at least five servings per day of a combination of vegetables and fruits. More would be even better. If you eat these plant foods generously, you will easily get the recommended amount of vitamin C, carotenoids and selenium," Schafer said.
"Some people think if they take supplements and get a fairly large amount of dietary antioxidants they will prevent all sorts of diseases. But a direct connection between the intake of antioxidants and the prevention of chronic disease has yet to be adequately established," Schafer said.
Highlights of the Natural Academy of Sciences report follow. The 38-page executive summary can be found on the internet at: http://www.nap.edu/readingroom/books/dri_vitaminc/summary.pdf.
Vitamin C: Women should consume 75 milligrams and men 90 milligrams to achieve the recommended daily dose. This is an increase from 60 mg for all adults. Smokers need an additional 35 mg per day because they are more likely to suffer from biological processes that damage cells and deplete vitamin C. The new recommendation is a significant increase but still easy to meet by eating ordinary foods. For example, an 8-ounce glass of orange juice has 97 mg and a cup of strawberries has 84 mg of vitamin C. Other food sources include oranges, grapefruit, broccoli, potatoes and leafy green vegetables. Consuming more than 2,000 mg per day may cause diarrhea.
Vitamin E: Both men and women should consume 15 milligrams or 22 International Units (IU) per day. Food sources include vegetable oils, seeds, nuts and green leafy vegetables.
The tolerable upper level for adults is 1,000 milligrams of alpha-tocopherol per day. Greater amounts may cause hemorrhagic damage because vitamin E can act as an anticoagulant and prevent blood from clotting.
Selenium: 55 micrograms is the recommended daily amount for adult men and women. Food sources include seafood, meat and whole grains. Consuming more than 400 micrograms per day could cause selenosis, a toxic reaction marked by hair loss and nail sloughing.
Beta-carotene and other carotenoids: The report does not include recommended daily intake or upper intake levels. The body has a natural mechanism that prevents overdosing on carotenoids from natural foods. However, research with beta-carotene in pill form showed some adverse effects on health. Because data is inconsistent, people should exercise caution before taking in high doses or pill forms.
For additional information, contact Elisabeth Schafer, Iowa State Extension nutritionist, at (515) 294-1359.
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