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

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.

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

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).

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

Incidence of type 2 DM.

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.

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.