beta-carotene supplementation and incidence of cancer and cardiovascular disease: The Women's Health Study

Background: In observational studies, individuals with high intakes of frui ts and vegetables containing beta-carotene experience lower risks of develo ping cancer. However, the few randomized trials of beta-carotene supplement ation show no overall benefits; some even suggest harm. This trial was desi gned to test the effects of beta-carotene supplementation in women. Methods : The Women's Health Study is a randomized, double-blind, placebo-controlle d trial originally testing aspirin, vitamin E, and beta-carotene in the pre vention of cancer and cardiovascular disease among 39 876 women aged 45 yea rs or older. The beta-carotene component was terminated early after a media n treatment duration of 2.1 years (range = 0.00-2.72 years). Statistical te sts were two-sided. Results: Among women randomly assigned to receive beta- carotene (50 mg on alternate days; n = 19 939) or placebo (n = 19 937), the re were no statistically significant differences in incidence of cancer, ca rdiovascular disease, or total mortality after a median of 4.1 years (2.1 y ears' treatment plus another 2.0 years' follow-up). There were 378 cancers in the beta-carotene group and 369 cancers in the placebo group (relative r isk [RR] = 1.03; 95% confidence interval [CI] = 0.89-1.18). There were no s tatistically significant differences for any site-specific cancer or during years 1 and 2 combined and years 3 and up combined. For cardiovascular dis ease, there were no statistically significant differences for myocardial in farction (42 in the beta-carotene group versus 50 in the placebo group), st roke (61 versus 43), deaths from cardiovascular causes (14 versus 12), or t he combined end point of these three events (116 versus 102; among women wi th more than one event, only the first was counted). Deaths from any cause were similar in the two groups (59 versus 55), Among smokers at baseline (1 3% of all women), there were no statistically significant differences in ov erall incidence of cancer OUR = 1.11; 95% CI = 0.78-1.58) or cardiovascular disease (RR = 1.01; 95% CI = 0.62-1.63), Conclusion: Among apparently heal thy women, there was no benefit or harm from beta-carotene supplementation for a limited period on the incidence of cancer and of cardiovascular disea se.