Effects of supplemental α-tocopherol and β-carotene on colorectal cancer: results from a controlled trial (Finland)

Abstract

Background:Some epidemiological investigations suggest that higher intake or biochemical status of vitamin E and β-carotene might be associated with reduced risk of colorectal cancer. Methods:We tested the effects of α-tocopherol and β-carotene supplementation on the incidence of colorectal cancer in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study, a double-blind, placebo-controlled trial among 29,133 50–69-year-old male cigarette smokers. Participants were randomly assigned to receive α-tocopherol (50 mg), β-carotene (20 mg), both agents, or a placebo daily for 5–8 years. Incident colorectal cancers (n = 135) were identified through the nationwide cancer registry, and 99% were histologically confirmed. Intervention effects were evaluated using survival analysis and proportional hazards models. Results:Colorectal cancer incidence was somewhat lower in the α-tocopherol arm compared to the no α-tocopherol arm, but this finding was not statistically significant (relative risk (RR) = 0.78, 95% confidence interval (CI) 0.55–1.09; log-rank test p = 0.15). β-Carotene had no effect on colorectal cancer incidence (RR=1.05, 95% CI 0.75–1.47; log-rank test p = 0.78). There was no interaction between the two substances. Conclusion:Our study found no evidence of a beneficial or harmful effect for β-carotene in colorectal cancer in older male smokers, but does provide suggestive evidence that vitamin E supplementation may have had a modest preventive effect. The latter finding is in accord with previous research linking higher vitamin E status to reduced colorectal cancer risk.