Objective: To examine the development of age-related cataract in a trial of beta carotene supplementation in men.
Design: Randomized, double-masked, placebo-controlled trial.
Methods: Male US physicians aged 40 to 84 years (n = 22 071) were randomly assigned to receive either beta carotene (50 mg on alternate days) or placebo for 12 years.
Main outcome measures: Age-related cataract and extraction of age-related cataract, defined as an incident, age-related lens opacity, responsible for a reduction in best-corrected visual acuity to 20/30 or worse, based on self-report confirmed by medical record review.
Results: There was no difference between the beta carotene and placebo groups in the overall incidence of cataract (998 cases vs 1017 cases; relative risk [RR], 1.00; 95% confidence interval [CI], 0.91-1.09) or cataract extraction (584 vs 593; RR, 1.00; 95% CI, 0.89-1.12). In subgroup analyses, the effect of beta carotene supplementation appeared to be modified by smoking status at baseline (P =.02). Among current smokers, there were 108 cases of cataract in the beta carotene group and 133 in the placebo group (RR, 0.74; 95% CI, 0.57-0.95). Among current nonsmokers, there was no significant difference in the number of cases in the 2 treatment groups (884 vs 881; RR, 1.03; 95% CI, 0.94-1.13). The results for cataract extraction appeared to be similarly modified by baseline smoking status (P =.05).
Conclusions: Randomized trial data from a large population of healthy men indicate no overall benefit or harm of 12 years of beta carotene supplementation on cataract or cataract extraction. However, among current smokers at baseline, beta carotene appeared to attenuate their excess risk of cataract by about one fourth.