Cardiovascular disease such as coronary artery disease, stroke and congestive heart failure, is a leading cause of death worldwide. A postulated risk factor is elevated circulating total homocysteine (tHcy) levels which is influenced mainly by blood levels of cyanocobalamin (vitamin B12), folic acid (vitamin B9) and pyridoxine (vitamin B6). There is uncertainty regarding the strength of association between tHcy and the risk of cardiovascular disease.
To assess the clinical effectiveness of homocysteine-lowering interventions (HLI) in people with or without pre-existing cardiovascular disease.
We searched The Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library (issue 3 2008), MEDLINE (1950 to August 2008), EMBASE (1988 to August 2008), and LILACS (1982 to September 2, 2008). We also searched in Allied and Complementary Medicine (AMED; 1985 to August 2008), ISI Web of Science (1993 to August 2008), and the Cochrane Stroke Group Specialised Register (April 2007). We hand searched pertinent journals and the reference lists of included papers. We also contacted researchers in the field. There was no language restriction in the search.
We included randomised clinical trials (RCTs) assessing the effects of HLI for preventing cardiovascular events with a follow-up period of 1 year or longer. We considered myocardial infarction and stroke as the primary outcomes. We excluded studies in patients with end-stage renal disease.
Data collection and analysis
We independently performed study selection, risk of bias assessment and data extraction. We estimated relative risks (RR) for dichotomous outcomes. We measured statistical heterogeneity using I2. We used a random-effects model to synthesise the findings.
We included eight RCTs involving 24,210 participants with a low risk of bias in general terms. HLI did not reduce the risk of non-fatal or fatal myocardial infarction, stroke, or death by any cause (pooled RR 1.03, 95% CI 0.94 to 1.13, I2 = 0%; pooled RR 0.89, 95% CI 0.73 to 1.08, I2 = 15%); and pooled RR 1.00 (95% CI 0.92 to 1.09, I2: 0%), respectively.
Results from available published trials suggest that there is no evidence to support the use of HLI to prevent cardiovascular events.
Plain language summary
B-complex vitamin therapy for preventing cardiovascular events
Cardiovascular disease is the number one cause of death worldwide. The most common causes of its morbidity and mortality are ischaemic heart disease, stroke and congestive heart failure. Many people with cardiovascular diseases may be asymptomatic, and might have high risk for developing a myocardial infarction, angina pectoris, stroke (ischaemic, haemorrhagic or both). ‘Emergent or new risk factors’ for cardiovascular disease have been recently added to the established risk factors (diabetes mellitus, high blood pressure, active smoker, adverse blood lipid profile). One of these risk factors is an elevated circulating total homocysteine (tHcy) levels. Homocysteine is an amino acid, and its levels in blood are influenced by blood levels of B-complex vitamins: cyanocobalamin (B12), folic acid (B9) and pyridoxine (B6). High tHcy levels are associated with an increased risk for atherosclerotic diseases. Hence, it has been suggested that B vitamins supplementation might reduce the risk of myocardial infarction, stroke, angina pectoris. Preventive strategies might include healthy people with low or high risk for developing cardiovascular disease (primary prevention) and people with an established cardiovascular disease (secondary prevention). In this review we included eight randomised controlled trials equivalent to 24,210 participants. We found no evidence that homocysteine-lowering interventions, in the form of supplements of vitamins B6, B9 or B12 given alone or in combination, at any dosage compared with placebo or standard care, prevents myocardial infarction, stroke, or reduces total mortality in participants at risk or with established cardiovascular disease. —Cochrane Review