β-Carotene Supplementation and Incidence of Cancer and Cardiovascular Disease: the Women's Health Study

Abstract

BACKGROUND: In observational studies, individuals with high intakes of fruits and vegetables containing β-carotene experience lower risks of developing cancer. However, the few randomized trials of β-carotene supplementation show no overall benefits; some even suggest harm. This trial was designed to test the effects of β-carotene supplementation in women. METHODS: The Women's Health Study is a randomized, double-blind, placebo-controlled trial originally testing aspirin, vitamin E, and β-carotene in the prevention of cancer and cardiovascular disease among 39 876 women aged 45 years or older. The β -carotene component was terminated early after a median treatment duration of 2.1 years (range = 0.00-2.72 years). Statistical tests were two-sided. RESULTS: Among women randomly assigned to receive β-carotene (50 mg on alternate days; n = 19 939) or placebo (n =19 937), there were no statistically significant differences in incidence of cancer, cardiovascular disease, or total mortality after a median of 4.1 years (2.1 years' treatment plus another 2.0 years' follow-up). There were 378 cancers in the β-carotene group and 369 cancers in the placebo group (relative risk [ RR] = 1.03; 95% confidence interval [CI] = 0.89-1.18). There were no statistically significant differences for any site-specific cancer or during years 1 and 2 combined and years 3 and up combined. For cardiovascular disease, there were no statistically significant differences for myocardial infarction (42 in the β-carotene group versus 50 in the placebo group), stroke (61 versus 43), deaths from cardiovascular causes (14 versus 12), or the combined end point of these three events (116 versus 102; among women with 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 (13% of all women), there were no statistically significant differences in overall incidence of cancer (RR = 1.11; 95% CI = 0.78-1.58) or cardiovascular disease (RR = 1.01; 95% CI = 0.62-1.63). CONCLUSION: Among apparently healthy women, there was no benefit or harm from β-carotene supplementation for a limited period on the incidence of cancer and of cardiovascular disease.