Selenium doesn’t prevent prostate cancer
Selenium supplements do not reduce the risk of any cancers, including prostate cancer, a recent Cochrane review has confirmed (http://cochranelibrary-wiley.com/doi/10.1002/14651858.CD005195.pub4/abstract).
The latest review to investigate this long-standing issue included 10 randomised-controlled trials (RCTs) and 70 observational studies in which adults were followed over time to determine whether their baseline selenium status was associated with their risk of cancer.
All of the high-quality RCTs reported no effect of selenium on reducing overall risk of cancer or risk of particular cancers, including the most investigated outcome – prostate cancer. In RCTs the relative risk of prostate cancer mortality in four studies involving 18 942 participants was 1.01 (95% CI 0.90–1.14). Of concern, some trials suggested that selenium may increase risks of high-grade prostate cancer.
From the late 1960s, a few observational studies reported that people with high levels of selenium in their diet or in their body tissues had lower risk of cancer, and some laboratory studies showed that selenium could inhibit the growth of cancer cells. Since then studies of variable quality have failed to provide a definitive answer and people continue to take selenium supplements for the prevention of various cancers.