Vitamin E and selenium: No magic bullet against prostate cancer

The National Cancer Institute has halted the testing of vitamin E and selenium for preventing prostate cancer after early trial results showed that the supplements not only didn't help but might actually cause harm. An independent review suggested that men in the study who took only vitamin E were slightly more likely to develop prostate cancer than those taking just selenium, a combination of the supplements, or placebos. The study also suggested that those who took only selenium developed more cases of type-2 diabetes. While the NCI said both findings could be due to chance, the study clearly showed that neither mineral, alone or in combination, had the hoped for effect of warding off prostate cancer.

Those findings continue the long run of disappointing results for antioxidant supplements. As we recently noted, 67 previous trials of various antioxidant pills produced only one positive result—a reduced risk of mortality that was cited in some, but not all, of the selenium trials. Vitamin C trials showed no benefits, while beta-carotene, vitamin A, and vitamin E supplements were actually linked to an increased risk of death.

Vitamin E pills have had a particularly bad run. A series of three other vitamin E studies published in recent years found that moderate to large doses did not reduce the risk of Alzheimer's disease, cancer, or cardiovascular disease. And one of those studies linked the supplement to an increased risk of heart failure in people with clogged arteries or diabetes. Another suggested that people being treated for head or neck cancers who take supplemental doses of vitamin E could triple their risk of developing a new cancer.

Why have these clinical trials of supplements—which attempt to document the benefits of specific vitamins and minerals by giving volunteers pills containing the nutrients—proved so ineffective, while earlier observational research had seemed so promising? One possible explanation is that many of those earlier studies had focused on diet, not pills, and their positive results stemmed from the thousands of other healthful phytochemicals found in fruits and vegetables. Or perhaps the nutrients only provide benefits when consumed with other compounds found in food. Furthermore, high doses used in many of the supplement trials may pose health risks.

CR's Take: We have long recommended getting your minerals, vitamins, and other nutrients from whole foods whenever possible. A diet that includes a wide range of fruits and vegetables as well as nuts, legumes, and whole grains provides a broad collection of potentially protective nutrients . For maximum diversity, try to consume foods from different color groups—red, orange, yellow, green, purple, and white—since each generally contains their own set of unique phytochemicals. Variety is not only the spice of life, it may very well protect it.

—Kevin McCarthy, associate editor

For advice on when taking supplemental vitamins and minerals can make sense, see our full report on filling your nutritional gaps. And subscribers can get information on more than 200 supplements on our Natural Health page.