Advanced prostate cancer risk in relation to toenail selenium levels.

BACKGROUND Selenium may prevent advanced prostate cancer (PCa), but most studies on this topic were conducted in populations with moderate to high selenium status. We investigated the association of toenail selenium, reflecting long-term selenium exposure, and advanced PCa risk in a population from the Netherlands where low selenium status is widespread. METHODS The analysis was conducted in the prospective Netherlands Cohort Study, which included 58 279 men aged 55 to 69 years at baseline in 1986. All cohort members completed a baseline questionnaire, and approximately 79% of participants provided toenail clippings, which were used for toenail selenium measurements using instrumental neutron activation analysis. Incident advanced PCa case subjects from the entire cohort were identified during 17.3 years of follow-up. The study employed a case-cohort design for which a random subcohort was sampled at baseline. Hazard ratios and 95% confidence intervals (CIs) were estimated using Cox proportional hazards regression models. All tests were two-sided. RESULTS Complete toenail selenium data were available for 898 advanced (International Union Against Cancer stage III/IV) PCa case subjects and 1176 subcohort members. The average toenail selenium concentration of subcohort members was 0.550 µg/g. Toenail selenium was associated with a reduced risk of advanced PCa; adjusted hazard ratio for the highest vs lowest quintile was 0.37 (95% CI = 0.27 to 0.51; P trend < .001). For stage IV PCa, men in the highest vs lowest quintile of toenail selenium had an adjusted hazard ratio of 0.30 (95% CI = 0.21 to 0.45; P trend < .001). CONCLUSIONS Toenail selenium was associated with a substantial decrease in risk of advanced PCa.