Nutrition Column: Effectiveness of Antioxidant Supplements Called into Question

Over the past several years, large population studies have continued to show that people whose diets were high in antioxidants, including vitamins A, C and E, tend to be at lower risk of heart disease and cancer. These findings have encouraged many Americans to take high levels of antioxidant supplements with the hope of warding off chronic disease. Today, it’s estimated that Americans spend more than $300 million a year on antioxidant supplements alone.

The workings of food and lifestyle, however, don’t translate well into pill form. In fact, based on recent findings, scientists now are beginning to question the efficacy of using antioxidant supplements beyond what is normally found in a healthful diet. The old adage, "If a little is good, more is better," has again come up short.

What went wrong? The large population studies released a decade ago suggesting that diets high in antioxidants were associated with lower risk for heart disease and cancer were not controlled clinical trials, but simply observations of what people ate, how they lived and what diseases they got.

To test the hypothesis that antioxidant vitamins were in fact the key component in the health of the observed, lower-risk group, several controlled clinical trials were begun in which subjects were randomly assigned to take one or more antioxidant supplements or a placebo. The outcomes were evaluated over a period of time. The results of these studies now are being published, and in general do not favor taking antioxidant supplements, particularly in large doses.

For example, a British study involving 20,000 people found that participants who took vitamins C, E and beta-carotene were not any better protected against heart disease or stroke than

those who did not. Moreover, results from the Harvard’s Women’s Health Study showed that the 20,000 women who took beta-carotene supplements every other day were not better protected from cancer than the women taking placebos.

Notably, a few studies have indicated that taking high doses of antioxidants in pill form may be harmful for some people. One recently published study suggested that people who take prescription statin drugs (a cholesterol-lowering medication) in conjunction with supplemental antioxidants might lose some of the heart-protecting benefits provided by the statin medication. In another study, smokers, former smokers and workers exposed to asbestos who took high levels of beta-carotene supplements were 30 percent more likely to develop lung cancer than those who did not.

More than anything, the results of these clinical trials have underscored the complexity of how nutrients and phytochemicals interact in food and in the body and what can happen when you overload the body with one nutrient or form of a nutrient, perhaps blocking the action of another.

In short, there is much more to be learned about the role of antioxidant nutrients in health and disease. Currently, vitamin E is being investigated to see if it may aid in preventing Alzheimer’s disease and in relieving arthritis symptoms. Carotenoids, other than beta-carotene, are being studied to see if they may help protect against macular degeneration and various other diseases.

In the meantime, one thing is sure – it’s important to continue to eat lots of antioxidant-rich fruits and vegetables. Although antioxidant supplements have not been linked to heart disease and cancer prevention, foods rich in antioxidants have repeatedly been shown to be beneficial in hundreds of research studies.