By Marc Garnick, M.D.
Health myths die hard. A recent article on healthy aging in the Washington Post suggested that taking vitamin E can help men prevent prostate and other cancers. That certainly isn’t what the evidence shows. In fact, a key clinical trial of vitamin E was stopped early because it showed that taking a vitamin E supplement failed to prevent prostate cancer and could—emphasis on could—promote prostate cancer.
Early cell culture and animal studies put a spotlight on vitamin E. Under controlled conditions, it was shown to slow prostate cancer growth. But as is so often the case in medical research, these results haven’t held up in humans.
Back in 1998, the Alpha-Tocopherol, Beta-Carotene (ATBC) Cancer Prevention Trial raised hopes that taking vitamin E supplements could lower prostate cancer risk. (Alpha-tocopherol is the most active of the eight naturally occurring forms of vitamin E.) The trial found that men who took daily alpha-tocopherol supplements experienced 32% fewer prostate cancer diagnoses and 41% fewer prostate cancer deaths than men who took a placebo. While promising, these results weren’t considered conclusive. That’s because the ATBC trial wasn’t specifically designed to evaluate prostate cancer risk, and almost all of the participants were Caucasian smokers.
To clarify the ATBC results, the Selenium and Vitamin E Cancer Prevention Trial (SELECT) was specifically designed to assess the effect of supplemental vitamin E on prostate cancer risk. As its name suggests, SELECT also looked at whether another antioxidant nutrient, selenium, affects cancer risk. All of the 35,533 participants were men aged 50 who did not have prostate cancer, and nearly one quarter were minorities. Participants were randomly assigned to take daily pills that contained alpha-tocopherol, selenium, both, or neither. The trial was initially planned to continue for 12 years, with five scheduled interim analyses.
At the second interim analysis in September 2008, the trial’s Data and Safety Monitoring Committee concluded that neither vitamin E nor selenium—alone or in combination—offered protection against prostate cancer. In fact, the monitoring committee noted that the rate of prostate cancer in the vitamin E group was slightly higher than the rates in the other three groups. The difference was not statistically significant, meaning it might have been due to chance, but the trend was worrisome. The committee decided to stop the trial early, and participants were told to stop taking their supplements in October 2008.
SELECT had some limitations. For example, the researchers did not test different doses or formulations of vitamin E. But SELECT’s robust design and large number of participants make its results trustworthy. The results are also likely to be widely applicable, due to the trial’s substantial proportion of non-white men and equal distribution of prostate cancer risk factors across all four study groups.
We know that eating a healthy, balanced diet can help prevent prostate cancer. Based on the results of the SELECT trial, I strongly discourage my patients from taking supplemental vitamin E or selenium. Though surprised, nearly all heed this advice and, in the process, many become more educated consumers of supplements and neutraceuticals.
Cancer prevention trial (SELECT) comes to a halt