Selenium supplementation has no effect on serum glucose levels in men at high risk of prostate cancer

Background: 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. Methods: 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 400μg/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. Results: Of the total 2893 glucose measurements, 734 were performed when the subject had been fasting for ≥8h. Changes in serum glucose levels during the course of the trial did not differ significantly between the placebo and selenium 200μg/day (P=0.98) and 400μg/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. Conclusion: These results do not support a relationship between selenium supplementation and risk of diabetes. Hence, recommendations regarding selenium supplementation based on increased risk of diabetes seem premature.