The role of antioxidants in preventive cardiology.

Vitamin C, carotenoids, and vitamin E, the three main dietary sources of antioxidants, each effect lipid peroxidation and may reduce atherogenesis and lower the risk of coronary heart disease (CHD). Crosscultural studies of antioxidants find that regions with relatively low dietary intake tend to have higher rates of CHD, but in these studies it is difficult to account for other important cardiovascular risk factors. Evidence from observational studies with more detailed information do not support a cardiovascular benefit for vitamin C, although the cardiovascular effect of vitamin C supplementation among populations with marginal vitamin C deficiency is not known. Results from recent clinical trials of beta-carotene supplementation show no cardiovascular benefit, although several observational studies have found an inverse association between carotenoid intake or plasma levels and risk of CHD. The benefit reported in the observational studies may be due to consumption in foods rich in beta-carotene rather than the beta-carotene itself. The evidence for a cardiovascular benefit of antioxidants is strongest for vitamin E. Three large prospective studies find that vitamin E supplement users have approximately 40% lower rates of CHD. Short durations and doses of less than 100 IU/d (when data were available) have no significant effect. The effect of dietary vitamin E may be more modest but still associated with lower risk of CHD in populations in which vitamin E supplementation is infrequent. In a large randomized trial, a nonsignificant reduction in CHD risk was reported for 50 IU/d, although the dose may have been insufficient. A secondary prevention trial of 400 and 800 IU/day reported a strong reduction in nonfatal myocardial infarction, further supporting the large body of evidence that suggests that high doses of vitamin E reduce risk of CHD.