Selenium yeast is a common dietary supplement used to provide selenium, an essential trace mineral. Scientific evidence suggests that selenium plays a role in supporting prostate health, primarily due to its antioxidant properties and involvement in DNA synthesis and repair. Several observational studies have associated higher selenium status with a reduced risk of prostate cancer. For example, some large-scale epidemiological studies have reported an inverse relationship between selenium levels and prostate cancer incidence, particularly in populations with low baseline selenium intake.

However, randomized controlled trials (RCTs) have provided mixed results. The Selenium and Vitamin E Cancer Prevention Trial (SELECT), one of the largest RCTs on this topic, did not find a statistically significant reduction in prostate cancer risk with selenium supplementation (including selenium yeast) in men with adequate selenium status. Additionally, some analyses suggest the possibility of harm or no benefit in those with already sufficient selenium intake.

Overall, while there is a scientific basis for the use of selenium yeast in supporting prostate health, particularly in men with low selenium levels, the evidence is not uniformly strong or conclusive, and supplementation in selenium-replete individuals is not clearly beneficial. This results in a moderate evidence rating.