A randomized, 12-year primary-prevention trial of beta carotene supplementation for nonmelanoma skin cancer in the physician's health study.

CONTEXT: Although basic research provides plausible mechanisms for benefits of beta carotene supplementation on nonmelanoma skin cancer (NMSC) primarily consisting of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), observational studies are inconsistent. Randomized trial data are limited to 1 trial of secondary prevention that showed no effect of beta carotene on the incidence of NMSC after 5 years.

OBJECTIVE: To test whether supplementation with beta carotene reduces the risk for development of a first NMSC, including BCC and SCC.

DESIGN: Randomized, double-blind, placebo-controlled trial with 12 years of beta carotene supplementation and follow-up.

SETTING: Physicians' Health Study in the United States.

PARTICIPANTS: Apparently healthy male physicians aged 40 to 84 years in 1982 (N = 22 071).

INTERVENTION: Beta carotene, 50 mg, on alternate days.

MAIN OUTCOME MEASURE: Relative risk (RR) and 95% confidence interval (CI) for a first NMSC, BCC, and SCC.

RESULTS: After adjusting for age and randomized aspirin assignment, there was no effect of beta carotene on the incidence of a first NMSC (RR, 0.98; 95% CI, 0.92-1.05), BCC (RR, 0.99; 95% CI, 0.92-1.06), or SCC (RR, 0.97; 95% CI, 0.84-1.13). There was also no significant evidence of beneficial or harmful effects of beta carotene on NMSC by smoking status (current, past, or never).

CONCLUSION: This large-scale, randomized, primary prevention trial among apparently healthy well-nourished men indicates that an average of 12 years of supplementation with beta carotene does not affect the development of a first NMSC, including BCC and SCC.