B-complex vitamins may fail to prevent cardiovascular events

Results from intervention trials suggest that there is no evidence to support the use of homocysteine-lowering B vitamins to prevent cardiovascular events, according to a new review.

In the review, eight randomized controlled trials with 24,210 participants were included. The researchers found no evidence that homocysteine-lowering interventions, in the form of supplements of vitamin B6, vitamin B9 or vitamin 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 (1).

However, experts criticized that there is a significant body of scientific literature to demonstrate that there is a link between B vitamins and a reduced risk of cardiovascular mortality. They said that the review is misleading as the majority of studies did not include participants with ‘high levels’ of homocysteine (between 15 and over 100 micromoles/liter) – the indicator for increased need for B vitamins. The mean starting level of 12.4 micromoles/liter in these trials could only be described as ‘moderately elevated.’

Cardiovascular disease is the number one cause of death worldwide. The most common causes of its morbidity and mortality are a reduced blood supply to the heart muscle (‘ischaemic heart disease’), stroke and congestive heart failure. Many people with cardiovascular diseases may show no symptoms, and might have high risk of developing a myocardial infarction and stroke. Among the new risk factors for cardiovascular disease that have been added to the established ones (diabetes mellitus, high blood pressure, active smoker, adverse blood lipid profile), elevated circulating homocysteine levels have been associated with an increased risk of atherosclerotic diseases.

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). Hence, it has been suggested that B vitamin supplementation might reduce the risk of myocardial infarction, stroke and angina pectoris. Preventive strategies might target healthy people with low or high risk for developing cardiovascular disease (primary prevention) and people with an established cardiovascular disease (secondary prevention).

However, there is uncertainty regarding the strength of association between homocysteine and the risk of cardiovascular disease. The researchers said that more large-scale, high-quality trials are needed to consolidate or challenge their findings.

1. Martí-Carvajal J et al. Homocysteine lowering interventions for preventing cardiovascular events. Cochrane Database of Systematic Reviews, Issue 4, 2009.