BOSTON, MASSACHUSETTS. At least five major clinical trials have concluded that higher levels of selenium (in blood or toenail clippings) are associated with a sharply reduced risk of prostate cancer. The Nutritional Prevention of Cancer (NPC) trial found that supplementing with 200 micrograms/day of selenium cuts prostate cancer risk in half. Researchers at the Harvard Medical School now weigh in with another study confirming the beneficial effects of selenium. Their study involved 22,000 healthy, male physicians who were enrolled in the study in 1982 and had blood samples taken at that time. Sufficient samples to analyze for selenium content and PSA level were available for 586 men diagnosed with prostate cancer as well as for 577 controls matched for age and smoking status.
After 13 years of follow-up the researchers concluded that study participants with a plasma selenium level of
0.12-0.19 ppm had a 50% lower incidence of advanced prostate cancer than did men with a level of 0.06-
0.09 ppm. The correlation was only apparent in men with a PSA level of more than 4 ng/mL and was
particularly strong for those with a baseline (1982) PSA level greater than 10 ng/mL. For these men a high
selenium level corresponded to a 70% decrease in the risk of advanced prostate cancer. The researchers
also observed a trend for a lower incidence of localized prostate cancer with high selenium levels, but this
trend was not statistically significant. They conclude that selenium is perhaps not too effective in preventing
the initiation of prostate cancer, but that it is highly effective in slowing down tumor progression. They
believe that selenium acts by selectively killing off cells whose DNA has been extensively damaged, by
inhibiting cellular proliferation, and by its role as a key component of glutathione peroxidase, which protects
cells from peroxide damage.
Editor's comment: The evidence is now indeed overwhelming that selenium helps protect against prostate cancer. While this study concluded that the protection mainly involves slowing down tumor progression, other studies have shown that selenium also helps prevent initiation of the cancer. Thus daily supplementation with 200 micrograms of selenium should be an integral part of all supplementation programs for men.