Long-term beta-carotene supplementation and risk of type 2 diabetes mellitus: a randomized controlled trial

JAMA. 1999 Sep 15;282(11):1073-5. doi: 10.1001/jama.282.11.1073.


Context: Recent data suggest a protective role of carotenoids in the development of type 2 diabetes mellitus (DM), possibly via an antioxidant effect, but no randomized trial has directly assessed the efficacy of beta-carotene to prevent DM.

Objective: To determine whether long-term beta-carotene supplementation reduces the risk of developing type 2 DM.

Design, setting, and participants: A total of 22, 071 healthy US male physicians aged 40 to 84 years in a randomized, double- blind, placebo-controlled trial, from 1982 to 1995. More than 99% of the participants had complete follow-up (median duration, 12 years).

Intervention: Subjects were randomly assigned to receive beta-carotene (50 mg on alternate days) or placebo.

Main outcome measure: Incidence of type 2 DM.

Results: A total of 10, 756 subjects were assigned to beta-carotene and 10, 712 to placebo. Incidence of type 2 DM did not differ between groups: 396 men in the beta-carotene group and 402 men in the placebo group developed type 2 DM (relative risk, 0.98; 95% confidence interval, 0.85-1.12). The lack of association between beta-carotene supplementation and incidence of type 2 DM persisted despite multivariate adjustment. There was no evidence of benefit when the period of risk was subdivided into years of follow-up or increasing duration of treatment.

Conclusion: In this trial of apparently healthy men, supplementation with beta-carotene for an average of 12 years had no effect on the risk of subsequent type 2 DM.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Aged
  • Antioxidants / therapeutic use*
  • Diabetes Mellitus, Type 2 / epidemiology
  • Diabetes Mellitus, Type 2 / prevention & control*
  • Dietary Supplements
  • Double-Blind Method
  • Humans
  • Incidence
  • Longitudinal Studies
  • Male
  • Middle Aged
  • Proportional Hazards Models
  • Risk
  • beta Carotene / therapeutic use*


  • Antioxidants
  • beta Carotene