Effect of selenium supplementation on changes in HbA1c: Results from a multiple-dose, randomized controlled trial

Aim To investigate the effect of selenium supplementation at different dose levels on changes in HbA1c after 6 months and 2 years in a population of low selenium status. Materials and Methods The Denmark PRECISE study was a single-centre, randomized, double-blinded, placebo-controlled, multi-arm, parallel clinical trial with four groups. In total, 491 volunteers aged 60 to 74 years were randomly assigned to treatment with 100, 200 or 300 mu g selenium/day as selenium-enriched yeast or placebo-yeast. HbA1c measurements were available for 489 participants at baseline, 435 at 6 months, and 369 after 2 years of selenium supplementation. Analyses were performed by intention to treat. Results The mean (SD) age, plasma-selenium concentration, and blood HbA1c at baseline were 66.1 (4.1) years, 86.5 (16.3) ng/g and 36.6 (7.0) mmol/mol, respectively. During the initial 6-month intervention period, mean HbA1c (95% CI) decreased by 1.5 (-2.8 to -0.2) mmol/mol for 100 mu g/d of selenium supplementation and by 0.7 (-2.0 to 0.6) mmol/mol for the 200 and 300 mu g/d groups compared with placebo (P = 0.16 for homogeneity of changes across the four groups). After 2 years of selenium supplementation, HbA1c had decreased significantly in all treatment groups, with no difference between active treatment and placebo. Conclusions Selenium supplementation in an elderly European population of low selenium status did not significantly affect HbA1c levels after 2 years. Our findings corroborate a possible U-shaped response of selenium supplementation on glucose metabolism.