Effects of long-term selenium supplementation on the incidence of type 2 diabetes: a randomized trial

Ann Intern Med. 2007 Aug 21;147(4):217-23. doi: 10.7326/0003-4819-147-4-200708210-00175. Epub 2007 Jul 9.


Background: Findings from animal models suggest that selenium supplementation improves glucose metabolism.

Objective: To examine the effect of long-term selenium supplementation on the incidence of type 2 diabetes.

Design: Secondary analysis of a randomized, double-blind, placebo-controlled trial.

Setting: Areas of low selenium consumption of the eastern United States.

Patients: 1202 persons seen in dermatology clinics who did not have type 2 diabetes at baseline.

Intervention: Oral administration of selenium, 200 microg/d, or placebo.

Measurements: Incidence of type 2 diabetes.

Results: During an average follow-up of 7.7 years (SD, 2.7), type 2 diabetes developed in 58 selenium recipients and 39 placebo recipients (incidence, 12.6 cases per 1000 person-years vs. 8.4 cases per 1000 person-years, respectively; hazard ratio, 1.55 [95% CI, 1.03 to 2.33]). The lack of benefit of selenium supplementation on the incidence of type 2 diabetes persisted in analyses stratified by age, sex, body mass index, and smoking status. An exposure-response gradient was found across tertiles of baseline plasma selenium level, with a statistically significantly increased risk for type 2 diabetes in the highest tertile of baseline plasma selenium level (hazard ratio, 2.70 [CI, 1.30 to 5.61]).

Limitations: Diabetes was a secondary outcome in the parent trial. Diagnoses of diabetes were self-reported but were validated in most participants. The sample was mostly older and white.

Conclusions: Selenium supplementation does not seem to prevent type 2 diabetes, and it may increase risk for the disease. Click here for related information on selenium.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Aged
  • Antioxidants / administration & dosage*
  • Antioxidants / adverse effects
  • Antioxidants / metabolism
  • Blood Glucose / metabolism
  • Diabetes Mellitus, Type 2 / blood
  • Diabetes Mellitus, Type 2 / epidemiology
  • Diabetes Mellitus, Type 2 / prevention & control*
  • Dietary Supplements* / adverse effects
  • Double-Blind Method
  • Female
  • Follow-Up Studies
  • Humans
  • Incidence
  • Male
  • Middle Aged
  • Risk Factors
  • Selenium / administration & dosage*
  • Selenium / adverse effects
  • Selenium / blood
  • Time Factors
  • United States


  • Antioxidants
  • Blood Glucose
  • Selenium