Selenium is a trace element essential to humans. Higher selenium exposure and selenium supplements have been suggested to protect against several types of cancers. However, this review found inconsistent results among randomized, controlled trials (RCTs).
Researchers reviewed 49 prospective observational studies and six RCTs. In epidemiologic data, they found a reduced cancer incidence and mortality with higher selenium exposure. Cancer risk was more pronouncedly reduced in men than in women. However, these findings have potential limitations due to study design, quality and heterogeneity of the data, which complicated the interpretation of the summary statistics, researchers said.
“The RCTs found no protective efficacy of selenium yeast supplementation against non-melanoma skin cancer or L-selenomethionine supplementation against prostate cancer. Study results for the prevention of liver cancer with selenium supplements were inconsistent and studies had an unclear risk of bias. The results of the Nutritional Prevention of Cancer Trial (NPCT) and SELECT raised concerns about possible harmful effects of selenium supplements.”
Authors said no reliable conclusions can be drawn regarding a causal relationship between low selenium exposure and an increased risk of cancer. “Despite evidence for an inverse association between selenium exposure and the risk of some types of cancer, these results should be interpreted with care due to the potential limiting factors of heterogeneity and influences of unknown biases, confounding and effect modification.”