The evidence was assessed of the effectiveness of vitamin supplementation, specifically vitamins A, C and E, β-carotene, folic acid, antioxidant combinations and multi-vitamin supplements, in preventing cardiovascular disease. The researchers selected English-language reports of randomised 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. Two reviewers abstracted descriptive information and data on cardiovascular outcomes and mortality from studies included. The researchers assessed study quality using predetermined criteria. Evidence tables were constructed to summarise data from studies included. The researchers summarised the strength, level and quality of the overall evidence for the effectiveness of each of the vitamin supplements in preventing or treating cardiovascular disease. Some good-quality cohort studies have reported an association between the use of vitamin supplements and lower risk for cardiovascular disease. Randomised, 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 analyse the cohort study data and to better design long-term clinical trials.