Antioxidant Supplements May Be Bad For You

We know that a diet high in fruits and vegetables can help you avoid heart disease as well several different types of cancers, including oral cancer, skin cancer, prostate cancer and colon or rectal cancers (News Bite 12/12/07). We also know that a diet rich in fruits and vegetables can help you avoid Alzheimer's Disease (News Bite 9/05/06). But what is it, exactly, that's so protective? Some studies suggest that the protective substances are the antioxidant vitamins, which include vitamins A, C, and E along with beta-carotene and selenium.

If that's true, then it would be reasonable to believe that antioxidant supplements in pill form would help protect you from illness or even make you better, right? After all, we know that the omega-3 fatty acids in fish oil supplements seem to work just as well as eating fish (News Bite 4/30/08). We in medicine know, however, that it's always wise to check our assumptions and look for evidence - that's why we call it "evidence-based medicine."

Recently the Cochrane Database of Systematic Reviews published a review article assessing the effects of antioxidant supplements (2008;2. Art. No. CD007176). A review article pools the data from multiple, similar studies to yield stronger, more definitive results than the smaller studies can on their own. In this article, the reviewers included 67 studies which involved over 232,000 people. Forty-six of the studies looked at the effect of antioxidant supplements on those who already had diseases such as cancer or heart disease, while twenty-one evaluated the supplements' effects on those who were healthy. For all of the studies, the reviewers calculated whether the subjects' risk of death were higher, lower, or the same when they were taking antioxidants.

Let's go back to our reasonable belief about antioxidants in pill form. Reasonable? Yes. True? Unfortunately, no. The results of the review show that supplements of beta-carotene, vitamin A, and vitamin E, whether given in combination or by themselves, actually increased the subjects' risk of death, regardless of whether the study was on those who were already ill or on those who were healthy. The results for vitamin C and selenium, however, were inconclusive.

What this means for you

It's clear that there's no substitute for good food. Indeed, this study shows that antioxidant supplements can actually harm you. Best to have a well-balanced diet with plenty of fruits and vegetables rather than trying to get your health from pills.

First posted: January 21, 2009