Because there is evidence that antioxidants may help prevent disease, millions of people are taking antioxidant supplements. In fact, it is estimated that 10%-20% of the adult population in North America and Europe take antioxidant supplements. But it is unclear whether these supplements are beneficial or harmful, with some studies even suggesting that they may increase the risk of death.
In the February 28, 2007 Journal of the American Medical Association , researchers looked at dozens of studies investigating the effects of antioxidant supplements. They found evidence that certain supplements were associated with an increased risk of death.
About the Study
The researchers identified 68 randomized controlled trials that followed 232,606 participants for an average of 3.3 years. Each trial compared the effects of antioxidant supplementation with a placebo or no intervention. The antioxidants were beta-carotene, vitamin A, vitamin C, vitamin E, and/or selenium, either singly or in combination. Each study was classified according to its methodological quality, with 47 studies being classified as high-quality and 21 being classified as lower-quality. The researchers investigated how the antioxidants affected the participants' risk of death.
When the results from all of the studies were pooled together, the antioxidant supplements had no significant effect on the risk of death. But when the researchers restricted their analyses to the high-quality studies (ie, those that were less likely to be biased), they found that beta-carotene, vitamin A, and vitamin E supplementation were associated with 7%, 16%, and 4% increases in the risk of death, respectively. Vitamin C and selenium had no significant effect on the risk of death, although selenium had a slight tendency to reduce the risk.
This study is limited because the average follow-up period was just over three years, so long-term effects of the antioxidants could not be determined. Also, the trials used widely varying antioxidant combinations and doses, with some of the trials using doses well above recommended amounts.
How Does This Affect You?
These findings suggest that antioxidant supplements, which are commonly used, may actually be harmful. So what does this mean for the millions of people who are taking these supplements? The decision of whether or not to take dietary supplements is an individual one, and depends on your health and family history of disease. But if you are taking antioxidant supplements, especially if you are taking high doses, these findings should prompt you to discuss their risks and benefits with your doctor.
Fruits and vegetables are rich in antioxidants, and there is no evidence that having high intakes of antioxidants from fruits and vegetables is associated with ill-effects. On the contrary, diets rich in fresh produce have been shown to reduce the risk of a number of diseases. So if you are looking to improve your health through nutrients, aim to get them through a healthful diet—not from a pill.
- Reviewer: Richard Glickman-Simon, MD
- Review Date: 04/2007 -