A vitamin E supplement significantly increased the incidence of prostate cancer in healthy men, according to a report published in the Journal of the American Medical Association. The findings are from an updated analysis from the Selenium and Vitamin E Cancer Prevention Trial (SELECT)—a study of more than 35,000 relatively healthy men aged 50 or older. SELECT was funded by the National Cancer Institute, NCCAM, and other components of the National Institutes of Health (NIH).
In the SELECT study, researchers randomly assigned participants into four treatment groups to receive daily doses of selenium (200 micrograms), vitamin E (400 international units [IU]), both selenium and vitamin E, or placebo. The initial study report stated that selenium and vitamin E taken alone or together did not prevent prostate cancer. Because of these findings, in 2008 participants were instructed to discontinue their study supplements. At that time, the researchers also noted that there was a slight increase in prostate cancer incidence in men who took vitamin E. However, the increase was not statistically significant, meaning there was a strong possibility that it could have been due to chance. Since 2008, researchers have continued to monitor the health of the study participants; this update is based on that continued monitoring.
At a median followup of 7 years, the researchers observed that the incidence of prostate cancer was increased by 17 percent in men who received the vitamin E supplement alone compared with those who received placebo. There was no increased incidence of prostate cancer when vitamin E and selenium were taken together.
The researchers noted that a biological explanation for the increased incidence of prostate cancer in the vitamin E group was not apparent from these data, but that the increased incidence became evident only after a longer period of monitoring. According to the researchers, this suggested that effects from these supplements may continue after treatment has ended. They also noted that these findings underscore the need for consumers to be skeptical of health claims in the absence of strong evidence of health benefits from clinical trials.
Klein EA, Thompson IM Jr, Tangen CM, et al. Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). Journal of the American Medical Association.; 306(14):1549–1556.2011