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 β-carotene
to prevent DM.
To determine whether long-term β-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).
Subjects were randomly assigned to receive β-carotene (50 mg on
alternate days) or placebo.
Main Outcome Measure
Incidence of type 2 DM.
A total of 10,756 subjects were assigned to β-carotene and 10,712
to placebo. Incidence of type 2 DM did not differ between groups: 396 men
in the β-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 β-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 β-carotene
for an average of 12 years had no effect on the risk of subsequent type 2