The potential benefits of selenium for prostate cancer prevention have generated a great deal of interest for a number of years.
At first, selenium was thought to be a beneficial nutrient by lowering the risk of prostate cancer. However, today we have much more information about the actual relationship between selenium and prostate cancer, and now know selenium is not useful.
Not that long ago, selenium was thought to provide some protection against the development of prostate cancer. Several observational studies had been performed seemingly showing that higher intake of selenium was associated with a lower risk of prostate cancer.
In fact, multiple studies seemed to show that higher levels of selenium in the blood were correlated with lower risks of prostate cancer. Many major news organizations picked up on these stories and soon much of the world thought of selenium as a potentially beneficial mineral for prostate cancer prevention.
Despite several seemingly convincing studies showing the benefit of selenium for prostate cancer prevention, many physicians were unsure as to the true benefits of this mineral. Because the development and progression of prostate cancer is not fully understood and thought to be quite complex, many physicians were skeptical as to the true potential benefits or harms of a single mineral in this complicated disease evolution.
Many prominent researchers pushed for a large, well-organized study of the true benefits of selenium for prostate cancer prevention.
The SELECT Trial
The SELECT (the Selenium and Vitamin E Cancer Prevention Trial) trial was the first large, well-organized, comprehensively controlled study that sought to evaluate the benefits of both selenium and vitamin E for prostate cancer prevention. The study was monitored and organized by several well respected researchers and research groups.
The SELECT trial enrolled more than 35,000 men who were randomly assigned to one of four groups over the course of several years. One group took one selenium and one vitamin E tablet daily. One group took one selenium and one placebo tablet daily. One group took one vitamin E and one placebo tablet daily. One group took two placebo tablets daily.
The SELECT trial overall showed no benefit in terms of prostate cancer risk reduction from taking selenium or vitamin E supplements. In addition, the trial showed a slight increase in the rate of diabetes among the men who were taking selenium supplements and a slight increase in the rate of prostate cancer in the men taking vitamin E supplements.
Neither of these slight increases in medical conditions were found to be statistically significant (meaning these small increases could be due to chance), however, they were still troubling enough when coupled with the lack of benefit of the supplements for the trial to be stopped early and the participants to be told to cease taking their supplements.
In large part due to the results of the SELECT trial, men today are generally no longer encouraged to take selenium and vitamin E supplements as a means to lower their prostate cancer risk.
Lippman SM, et al. Effect of Selenium and Vitamin E on Risk of Prostate Cancer and Other Cancers: The Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2009;301(1):39-51