Antioxidants are nutrients that prevent oxygen from combining with other substances and damaging cells. Since oxidation is thought to play a role in aging, antioxidants are widely believed to promote longevity. The three best known antioxidants are vitamins C and E and the mineral selenium.


Because people who eat foods rich in antioxidants have lower rates of cancer, cardiovascular disease, and other health problems, some experts advise taking daily supplements of these nutrients. Others argue that something else in the foods may be responsible, and that in fact supplements may be harmful.


In April 2000, the Food and Nutrition Board (FNB) issued new recommendations for antioxidants. While the FNB urged people to get more antioxidants in their diet, it said there was no proof that taking supplements is a good way to accomplish this. It also, for the first time, set safe upper limits on the three most important antioxidants.


Here's a brief summary on each:


   Vitamin C. Although for most people the Recommended Dietary Allowance (RDA) of vitamin C is less than 100 milligrams a day, many experts advise getting 250 to 500 milligrams, in part because high intake of vitamin-C-rich fruits and vegetables has been linked to a lower incidence of stomach and intestinal cancers.* This is still far below the FNB's safe upper limit. For details, see Vitamin C.


   Vitamin E. People who get more of this vitamin have fewer heart attacks and strokes. It appears to prevent buildup of plaque in arteries. In supplements, the usual dosage is 100 to 400 International Units (IU) per dayabout five to 18 times most people's RDA. Again, this is nowhere near the FNB's safe upper limit. See Vitamin E.


   Selenium. This mineral appears to help prevent stroke and cancer of the ovaries, prostate, colon, rectum, skin, and lung. Antioxidant supplements often include 50 micrograms of seleniumnot far from most people's RDA. The FNB's safe upper limit is eight times that level. See Selenium.


(Daily supplements of a fourth antioxidant, a precursor of vitamin A called beta-carotene, were popular until 1996, when long-term studies showed that the pills didn't prevent heart attack and stroke, as formerly believed. Some experts now think long-term use of beta-carotene may be harmful. In its April 2000 report, the FNB urged people to exercise caution when taking beta-carotene supplements, and recommended using them only to prevent or treat a vitamin-A deficiency.)


* But this doesn't prove that vitamin-C supplements prevent cancer. See Vitamin C.