Despite the positive link to stroke risk, data from 19 randomized controlled trials involving 47,921 participants suggested no benefits for B vitamin supplementation on the risk of cardiovascular disease (CVD), coronary heart disease or heart attack.
The meta-analysis represents the “most recent information available on the associations between B vitamins supplementations and risk of CVD”, said researchers from Zhejiang University in China, the National Health Research Institutes in Taiwan, and Monash University in Australia.
The potential role of B vitamins in heart health, by reducing levels of the amino acid homocysteine reported to increase the risk of cardiovascular disease, is controversial.
Epidemiological studies have linked increased blood levels of the amino acid homocysteine to an increased risk of cardiovascular disease (CVD). It has been suggested that by lowering the levels of homocysteine in the blood with B-vitamins, people could cut the risk of CVD.
However, clinical trials including participants at risk of, or already suffering from, cardiovascular disease have produced null results, with some experts arguing that short term B vitamin supplementation should not be expected to reverse the long-term development of heart disease.
In 2009 a prestigious Cochrane review concluded in that supplements of B6, B12 or folate do not affect cardiovascular health, despite lowering homocysteine levels. The review included data from eight randomized controlled trials equivalent to 24,210 participants.
While the new meta-analysis agrees that B vitamins did not affect the risk of cardiovascular disease (CVD), coronary heart disease or heart attack, it does challenge the conclusions regarding stroke risk.
Nineteen studies provided data obtained from intervention and follow-up periods ranging from 6 to 85 months, and doses of folic acid with or without vitamins B6 and B12.
Results showed that B vitamin supplementation was associated with significant reductions in homocysteine levels, and a 12% reduction in the risk of stroke, compared with placebo, but no differences were observed for other cardiovascular outcomes.
“The discrepancies between the RCTs of B vitamins supplementation for the prevention of CVD may have various explanations,” said the researchers.
“First, it is possible that populations without folate deficiency may not benefit from folic acid supplementation
“Second, RCTs may not avoid residual confounding. Different personal behaviors may modify the effects of dietary intake or supplement use on vascular disease. Then, the duration of follow-up and sample size may also contribute to differences between clinical trials.
“Third, trials to date have examined the effects of B vitamin supplementation for secondary prevention only.”
Source: Clinical Nutrition
Published online ahead of print, doi: 10.1016/j.clnu.2011.01.003
“Meta-analysis of B vitamin supplementation on plasma homocysteine, cardiovascular and all-cause mortality”
Authors: T. Huang, Y. Chen, B. Yang, J. Yang, M.L. Wahlqvist, D. Li