Cynthia D Morris1, Susan Carson. 1. Department of Medical Informatics and Clinical Epidemiology, Oregon Health & Science University Evidence-based Practice Center, 3181 SW Sam Jackson Park Road, Mail Code BICC, Portland, OR 97239, USA.
Abstract
BACKGROUND: Antioxidant vitamins are thought to play a role in atherosclerosis. Supplementation of these nutrients has been explored as a means of reducing cardiovascular morbidity and mortality. PURPOSE: To assess the evidence of the effectiveness of vitamin supplementation, specifically vitamins A, C, and E; beta-carotene; folic acid; antioxidant combinations; and multivitamin supplements, in preventing cardiovascular disease. DATA SOURCES: Cochrane Controlled Trials Registry and MEDLINE (1966 to September 2001), reference lists, and experts. STUDY SELECTION: The researchers selected English-language reports of randomized trials and cohort studies that assessed vitamin supplementation in western populations and reported incidence of or death from cardiovascular events. They also included reports of good- or fair-quality clinical trials of primary and secondary prevention and good- or fair-quality prospective cohort studies. Studies that examined only dietary nutrients or did not provide separate estimates for supplements were not included. DATA EXTRACTION: Two reviewers abstracted descriptive information and data on cardiovascular outcomes and mortality from included studies. The researchers assessed study quality using predetermined criteria. DATA SYNTHESIS: Evidence tables were constructed to summarize data from included studies. The researchers summarized the strength, level, and quality of the overall evidence for the effectiveness of each of the vitamin supplements in preventing or treating cardiovascular disease. CONCLUSIONS: Some good-quality cohort studies have reported an association between the use of vitamin supplements and lower risk for cardiovascular disease. Randomized, controlled trials of specific supplements, however, have failed to demonstrate a consistent or significant effect of any single vitamin or combination of vitamins on incidence of or death from cardiovascular disease. Understanding the sources of these differences will permit researchers to better analyze the cohort study data and to better design long-term clinical trials.
BACKGROUND: Antioxidant vitamins are thought to play a role in atherosclerosis. Supplementation of these nutrients has been explored as a means of reducing cardiovascular morbidity and mortality. PURPOSE: To assess the evidence of the effectiveness of vitamin supplementation, specifically vitamins A, C, and E; beta-carotene; folic acid; antioxidant combinations; and multivitamin supplements, in preventing cardiovascular disease. DATA SOURCES: Cochrane Controlled Trials Registry and MEDLINE (1966 to September 2001), reference lists, and experts. STUDY SELECTION: The researchers selected English-language reports of randomized trials and cohort studies that assessed vitamin supplementation in western populations and reported incidence of or death from cardiovascular events. They also included reports of good- or fair-quality clinical trials of primary and secondary prevention and good- or fair-quality prospective cohort studies. Studies that examined only dietary nutrients or did not provide separate estimates for supplements were not included. DATA EXTRACTION: Two reviewers abstracted descriptive information and data on cardiovascular outcomes and mortality from included studies. The researchers assessed study quality using predetermined criteria. DATA SYNTHESIS: Evidence tables were constructed to summarize data from included studies. The researchers summarized the strength, level, and quality of the overall evidence for the effectiveness of each of the vitamin supplements in preventing or treating cardiovascular disease. CONCLUSIONS: Some good-quality cohort studies have reported an association between the use of vitamin supplements and lower risk for cardiovascular disease. Randomized, controlled trials of specific supplements, however, have failed to demonstrate a consistent or significant effect of any single vitamin or combination of vitamins on incidence of or death from cardiovascular disease. Understanding the sources of these differences will permit researchers to better analyze the cohort study data and to better design long-term clinical trials.
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