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For years, antioxidants such as vitamins A, C, E, folic acid, and beta-carotene have been touted as having multiple health benefits, including preventing heart disease and cancer. But now a government panel of health experts says there is no clear evidence to support this claim.
And for smokers, taking beta-carotene supplements could even increase their risk of lung cancer and death, the panel says.
"We can't say that [people] should or they shouldn't take supplements," said Janet Allan, vice chair of the U.S. Preventative Services Task Force, which conducted the review. "We can't tell you if it will help or not."
The findings were published in the July 1 issue of the Annals of Internal Medicine.
Cynthia Morris, a researcher at Oregon Health & Science University who compiled and analyzed the studies, said that while supplements may have other benefits, they likely have no effect on cardiovascular health or cancer. Of people who take vitamins for the sole purpose of preventing disease, she says: "They're basically creating expensive urine." Smokers cautioned
The task force specifically recommended that people who smoke more than two packs of cigarettes a day should not take beta-carotene, either alone or in a multivitamin combination. But there is no evidence to suggest that beta-carotene is harmful to smokers at the levels that occur naturally in foods.
Vitamin supplements are a multibillion-dollar industry in the United States. But natural antioxidants are plentiful in fruits and vegetables, including leafy greens, citrus fruits, carrots, sweet potatoes and broccoli.
Allan said that most people can get all the nutrients they need by eating a healthy diet. Still she acknowledged that many people don't. The elderly, pregnant or lactating women, and people on certain medications have trouble absorbing nutrients from foods.
The U.S. Preventative Services Task Force scrutinized more than two dozen studies over two years. They analyzed the use of vitamins A, C, or E, multivitamins with folic acid, or antioxidant combinations to reduce the risk of cardiovascular disease, heart attack or sudden cardiac death. They also looked at the effectiveness of antioxidants for preventing several types of cancer including lung, prostate, colon, breast, and nonmelanoma skin cancer.
Antioxidant deficiencies have been linked to blood vessel changes that occur in cardiovascular disease and cellular changes that occur in cancer, leading some people to hypothesize that vitamin supplements might help prevent these diseases. But the studies reviewed by the task force did not bear this theory out. Use in moderation OK'd
Annette Dickinson, president of the Council for Responsible Nutrition, a trade association that represents the dietary supplement industry, pointed out that "cancer and heart disease are not the only --- or even the primary --- reasons for using vitamins." For example, folic acid supplements are recommended for women of childbearing age because it has been shown to prevent birth defects.
Most studies reviewed by the task force showed that there is no harm in taking vitamin supplements within the Recommended Daily Allowance. But some vitamins can have detrimental effects if taken in excess. For example, high doses of vitamin A can cause damage to the liver or the fetus of a pregnant woman.
The task force did not rule out the possibility that taking antioxidant supplements may have long-term health benefits. Most of the studies they reviewed only went on for three to five years.
There are a number of ongoing studies that may yield more answers. "In three to four years we'll have a lot more information," Allan said. "We can come back and look at the results of these studies and maybe make new recommendations."
She added: "If people have concerns about what they should be doing, they should talk to their physician."
Copyright 2003 The Atlanta Journal-Constitution