Epidemiologic studies have suggested that higher intakes of fruit, vegetables, and whole grain are related to a lower risk of coronary heart disease (CHD). One explanation for this finding is a reduction in oxidatively modified LDL, which is thought to play an important role in the development of atherosclerosis. Whether the association between these foods and CHD is due to antioxidant vitamins or some other factors remains unclear.
In the present Pooling Project of Cohort Studies on Diet and Coronary Disease, the authors studied the relations of the intakes of vitamin E, five carotenoids, and vitamin C to the incidence of all major CHD events and CHD mortality by pooling primary data from nine major cohorts studies. This large database enabled several issues to be examined, such as whether 1) single antioxidants or combinations of them predict CHD occurrence, 2) the strength of associations differs by dietary and supplemental intake and 3) non-dietary or dietary risk factors of CHD modify the association.
During a 10-year follow-up, 4,647 major incident CHD events occurred in 293,172 subjects who were free of CHD at baseline. Diet was measured by using a food frequency questionnaire in seven cohorts and by using a dietary history interview or food records in two cohorts. Overall intakes (dietary and supplemental combined) of vitamin E, beta-carotene, total carotene, and vitamin C were calculated.
There were significant inverse associations of intakes of energy-adjusted dietary vitamin E, alpha- and beta-carotene, lutein, and beta-cryptoxanthin with the incidence of all major CHD events in the pooled population not taking vitamin supplements. However, dietary intake of antioxidant vitamins was only weakly related to a reduced CHD risk after adjustment for potential non-dietary and dietary confounding factors. Subjects with higher supplemental vitamin C intake had a lower CHD incidence. Subjects in the highest quintile of vitamin C intake had a 24% lower risk than did those in the lowest quintile. Supplemental vitamin E intake was not significantly related to reduced CHD risk. A lower risk of major CHD events was found at higher total intakes of beta-carotene and at higher dietary intakes of several carotenoids after adjustment for age and energy intake.
The results of this study suggest that the use of vitamin C supplements may reduce CHD incidence in men and women. The findings weakly support the hypothesis that a higher dietary intake of vitamin E or lutein reduces the risk of CHD. However, further studies should be conducted regarding recommendations for high doses of vitamin C supplements.
Paul Knekt, John Ritz, Mark A Pereira, et al., Antioxidant vitamins and coronary heart disease rRisk: a pooled analysis of 9 cohorts, Am J Clin Nutr 80:1508--1520 (December 2004) [Address reprint requests to P Knekt, National Public Health Institute, Mannerheimintie 166, 00300 Helsinki, Finland. E-mail: firstname.lastname@example.org]
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