B vitamins may not prevent against second stroke

Stroke patients who take vitamin B supplements to lower their homocysteine levels may not be protected from second strokes or heart attacks, a new Australian study suggests.

In the randomized controlled trial, 8,164 patients with recent stroke or heart attack were randomly assigned to receive B vitamins (25 mg vitamin B6, 2 mg vitamin B9, and 0.5 mg vitamin B12) or placebo in addition to standard care (1). The patients were followed up for a mean duration of 3.4 years to assess the incidence of major vascular events. The researchers found that the B vitamins were no more effective than placebo in reducing the risk of a second stroke or heart attack. The B vitamins did, however, lower homocysteine levels and were well-tolerated.

The researchers said that the question of whether or not B vitamins lower the risk of a second stroke or heart attack was not answered fully by this trial. The study may not have included enough patients and may not have run for long enough to be statistically sound. Earlier studies suggest that raised plasma concentrations of total homocysteine might be a risk factor for major vascular events and that lowering homocysteine levels with B vitamins might reduce this risk.

Experts commented an important limitation is the fact that this trial tested B vitamins like drugs for secondary prevention of strokes in patients. The results of this study do not address the question of whether taking B vitamins can have a beneficial effect on primary prevention. Therefore, the study does not refute the findings from observational studies, which demonstrate a primary preventive effect of lower homocysteine levels on cardiovascular outcomes, they concluded (2).

1. Hankey G. J. et al. B vitamins in patients with recent transient ischaemic attack or stroke in the VITAmins TO Prevent Stroke (VITATOPS) trial: a randomised, double-blind, parallel, placebo-controlled trial. The Lancet Neurology. 2010.
2. Wang X. et al. Efficacy of folic acid supplementation in stroke prevention: a meta-analysis. Lancet 2007; 369: 1876–82.