A Prospective Study of Plasma Selenium Levels and Prostate Cancer Risk

Background: Epidemiologic studies suggest that low selenium levels are associated with an increased incidence of prostate cancer, although results are conflicting. We examined the association between pre-diagnostic plasma selenium levels and risk of prostate cancer in men enrolled in the Physicians' Health Study. Methods: Using plasma samples obtained in 1982 from healthy men enrolled in the study, we conducted a nested case–control study among 586 men diagnosed with prostate cancer during 13 years of follow-up and 577 control subjects. Odds ratios (ORs) and 95% confidence intervals (CIs) for the risk of prostate cancer in pre- (before October 1990) and post- (after October 1990) prostate-specific antigen (PSA) screening eras were calculated using multivariable logistic regression. Results: Pre-diagnostic plasma selenium levels were inversely associated with risk of advanced prostate cancer (5th versus 1st quintile OR = 0.52, 95% CI = 0.28 to 0.98; Ptrend = .05), even among men diagnosed after 1990 (5th versus 1st quintile OR = 0.39, 95% CI = 0.16 to 0.97). The inverse association with prostate cancer risk was observed only for case subjects with elevated baseline PSA levels (PSA >4 ng/mL, 5th versus 1st quintile OR = 0.49, 95% CI = 0.28 to 0.86; Ptrend = .002). These inverse associations were observed in both pre- and post-PSA eras. Conclusions: The inverse association between baseline plasma selenium levels and risk of advanced prostate cancer, even among men diagnosed during the post-PSA era, suggests that higher levels of selenium may slow prostate cancer tumor progression. Ongoing randomized trials of selenium supplements may help to further evaluate this issue.