Taking high doses of selenium or vitamin E could raise a man’s risk of prostate cancer.
Starting in 2001, the SELECT trial gave roughly 35,500 men either selenium (200 micrograms a day of selenomethionine), vitamin E (400 IU a day of synthetic alpha-tocopherol), both, or a placebo. In 2008, researchers stopped the trial three years early because it was clear that the supplements were not preventing prostate cancer.
In a new analysis, researchers compared 489 men in the study who were diagnosed with high-grade prostate cancer (a Gleason score of 7 to 10) during the trial to 3,117 men in the study without prostate cancer. The results:
■ Taking selenium roughly doubled the risk of high-grade prostate cancer among men who started the study with higher levels of selenium (measured in toenail samples), but not among men with lower levels.
■ Taking vitamin E roughly doubled the risk of high-grade prostate cancer among men who started the trial with lower selenium levels, but not among men with higher levels.
Among placebo takers, starting the trial with lower—or higher—selenium levels had no impact on the risk of prostate cancer.
What to do: Don’t take more than the Recommended Dietary Allowance for selenium (55 mcg) or vitamin E (22 IU). Scientists aren’t sure how to explain the results, which agree with other trials that found no lower—and possibly a higher—risk of cancer in people taking high doses of antioxidants.
Source: J. Natl. Cancer Inst. 2014. doi:10.1093/jnci/djt456 and doi:10.1093/jnci/dju005.