What Is the Scientific Evidence for Selenium?
Somewhat inconsistent evidence suggests that selenium supplements may help prevent cancer. Evidence from observational studies indicates that low intake of selenium is tied to increased risk of cancer. 39,40 However, such studies are notoriously unreliable as guidelines to therapy. Only double-blind trials can truly determine whether selenium supplements can help prevent cancer. (For information on why this is so, see Why Does This Database Rely on Double-blind Studies? ) The most important double-blind study on selenium and cancer was conducted by researchers at the University of Arizona Cancer Center. 37 In this trial, which began in 1983, 1,312 people were divided into two groups. One group received 200 mcg of yeast-based selenium daily; the other received placebo. Participants were not deficient in selenium, although their selenium levels fell toward the bottom of the normal range. The researchers were trying to determine whether selenium could lower the incidence of skin cancers.
