Vitamin E and selenium supplements, either taken independently or together, do not reduce a man's chances of developing prostate cancer, and may even heighten his risks, a federally funded study has found.
A seven-year trial involving more than 35,000 subjects and conducted at 400 sites around the United States was suspended this month, after researchers began tallying the effects and found, at best, no benefit and at worst, signs of trouble. Participants were told to stop taking their supplements and assured that their health would be monitored for roughly the next three years.
Researchers found a slightly elevated risk of prostate cancer in subjects taking only Vitamin E and a small increased risk of developing diabetes in men taking only selenium. The National Institutes of Health, which funded the study, cautioned that those small effects may have been due to chance. As they comb the evidence, the researchers should learn more about the relationship.
The preliminary results of what is known as the SELECT trial are a major disappointment to those who had hoped that an inexpensive, widely available dietary supplement might prove powerful in the prevention of cancer. Previous studies had suggested that selenium and Vitamin E, taken alone or together, might decrease the risk of developing prostate cancer by 60% and 30%, respectively.
But the latest study is not the first trial of supplements' cancer-prevention properties to end in disappointment: Studies completed in the 1990s found that beta-carotene supplementation failed to prevent lung cancer, and in fact appeared to increase the odds that male smokers would develop the disease.
In other clinical trials, researchers are exploring whether lycopene, a plant-based substance, might drive down the risk of prostate cancer for men. Drugs being studied as possible prostate cancer preventives include the anabolic steroid toremifene, the enlarged-prostate treatment dutasteride, and finasteride, which is widely prescribed for enlarged prostate and hair loss.