Selenium is an essential trace element for the human body, but worldwide, the intake of selenium varies greatly among people in different geographical areas due to different dietary structures. While selenium intake levels are high in the United States, they are still low in European regions. Previous studies have suggested that selenium may prevent the development of advanced prostate cancer, but the majority of studies addressing this issue have been conducted in populations with moderate or high selenium levels. Therefore, Milan S. Geybels et al. from the University of Maastricht in the Netherlands conducted a clinical study to investigate the association between toenail selenium levels (which reflect long-term selenium intake, in addition to the relatively low levels of selenium intake in the Netherlands) and the risk of prostate cancer, and published their findings in the latest online issue of JNCI in July. This analysis is a prospective study in which the investigators selected a cohort in the Netherlands that included 58,279 male subjects aged 55 to 69 years. Subjects completed a questionnaire at enrollment, and approximately 79% of subjects provided toenails of the toes for determination of selenium levels in the toes. After 17.3 years of follow-up, the investigators determined the number of patients with advanced prostate cancer in the entire cohort. This study was a case-cohort design study with a subcohort set at enrollment. The investigators applied a Cox risk regression proportional model to calculate risk ratios and 95% confidence intervals. All statistical tests were performed bilaterally. There were 898 patients with advanced prostate cancer (tumor stage III or IV) and 1176 patients in the subcohort who could provide complete data related to toenail selenium. The mean toenail selenium concentration in the subcohort subjects was 0.550 μg/g. Toenail selenium concentration was associated with a reduced risk of advanced prostate cancer, with a statistically significant adjusted risk ratio of 0.37 for subjects in the highest quartile and subjects in the lowest quartile. For patients with stage IV prostate cancer, the adjusted risk ratio for subjects in the highest quartile and subjects in the lowest quartile was 0.30, again with statistically significant results. The results of this study point out that toenail selenium content is associated with a reduced risk of advanced prostate cancer.