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

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.