A randomized, placebo-controlled trial of selenium supplementation in patients with type 2 diabetes: effects on glucose homeostasis, oxidative stress, and lipid profile.

Selenium is an antioxidant trace element. Patients with diabetes are shown to have increased oxidative stress together with decreased selenium concentrations. Whether raising serum selenium will improve blood glucose management in diabetes is largely unknown. In this randomized, double-blind placebo-controlled trial, we assessed the effects of selenium on blood glucose, lipid profile, and oxidative stress in 60 patients with type 2 diabetes. Selenium 200 µg/d or placebo was administered orally for 3 months. Serum concentrations of fasting plasma glucose, glycosylated hemoglobin A1c (HbA1c), insulin, and lipid profile, as well as ferric-reducing ability of plasma and thiobarbituric acid-reactive substances were determined in the fasting state at baseline and after 3 months. Mean (SD) serum selenium at baseline was 42.69 (29.47) µg/L and 47.11 (42.86) µg/L in selenium and placebo groups, respectively. At endpoint, selenium concentration reached to 71.98 (45.08) µg/L in selenium recipients compared with 45.38 (46.45) µg/L in placebo recipients (P<0.01). Between-group comparison showed that fasting plasma glucose, glycosylated hemoglobin A1c, and high-density lipoprotein cholesterol were statistically significantly higher in the selenium recipient arm. Other endpoints changes during the course of trial were not statistically different across the 2 treatment arms. This study suggests that selenium supplementation in patients with type 2 diabetes may be associated with adverse effects on blood glucose homeostasis, even when plasma selenium concentration is raised from deficient status to the optimal concentration of antioxidant activity. Until results of further studies become available, indiscriminate use of selenium supplements in patients with type 2 diabetes warrants caution.