Antioxidant vitamins intake and the risk of coronary heart disease: meta-analysis of cohort studies

BACKGROUND: Many epidemiological studies have reported that antioxidant vitamin intake from diet or supplements are associated with a lower risk of coronary heart disease (CHD), the findings are, however, inconsistent. We undertook a meta-analysis of cohort studies to examine the relations between antioxidant vitamins (vitamins C, E, and beta-carotene) and CHD risk. METHODS AND RESULTS: We included all the relevant cohort studies if they provided a relative risk and corresponding 95% confidence interval (CI) of CHD in relation to antioxidant vitamins intake from diet or supplement. Fifteen cohort studies were identified involving a total of 7415 incident CHD cases and 374,488 participants with a median follow-up of approximately 10, 8.5, and 15 years for vitamins C, E, and beta-carotene, respectively. Pooled estimates across studies were obtained by random-effects model. The potential sources of heterogeneity and publication bias were also estimated. For vitamins C, E, and beta-carotene, a comparison of individuals in the top third with those in the bottom third of baseline value yielded a combined relative risk of 0.84 (95% CI, 0.73-0.95), 0.76 (95% CI, 0.63-0.89), and 0.78 (95% CI, 0.53-1.04), respectively. Subgroup analyses show that dietary intake of vitamins C and E and supplement use of vitamin E have an inverse association with CHD risk, but supplement use of vitamin C has no significant association with CHD risk. In the dose-response meta-analysis, each 30 mg/day increase in vitamin C, 30 IU/day increase in vitamin E, and 1 mg/day increase in beta-carotene yielded the estimated overall relative risk for CHD of 1.01 (95% CI, 0.99-1.02), 0.96 (95% CI, 0.94-0.99), and 1.00 (95% CI, 0.88-1.14), respectively. CONCLUSIONS: Our findings in this meta-analysis suggest that an increase in dietary intake of antioxidant vitamins has encouraging prospects for possible CHD prevention.