['Current literature regarding the effect of selenium supplementation on the risk of diabetes is inconclusive. Hence, a longitudinal study was conducted to investigate the effect of selenium supplementation on serum glucose levels in elderly men.', 'Data were obtained from 699 men participating in a randomized double-blind placebo-controlled Phase 3 clinical trial investigating the effects of two doses of selenium (200 and 400 μg/day) compared with placebo on the incidence of prostate cancer. Subjects were followed every 6 months for up to 5 years. Serum glucose levels were obtained every 6 months. Mixed-effects regression models were used to assess whether the rate of change of serum glucose levels was significantly different in the selenium-supplemented groups compared with placebo. Sensitivity analyses were performed to assess the robustness of findings and to minimize the possibility of residual bias due to fasting status.', 'Of the total 2893 glucose measurements, 734 were performed when the subject had been fasting for ≥8 h. Changes in serum glucose levels during the course of the trial did not differ significantly between the placebo and selenium 200 μg/day (P = 0.98) and 400 μg/day (P = 0.81) groups. Sensitivity analyses demonstrated comparable results for models using the total population and models restricted to subjects with only fasting glucose data.'] Does selenium supplementation have no effect on serum glucose levels in men at high risk of prostate cancer?