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Earlier studies found an association between homocysteine, an amino acid, in the blood, and an increased risk for stroke and heart attack. Vitamin B supplements lower homocysteine levels, but whether this really has an effect on stroke and heart attack risk has been unclear, the Australian researchers noted.
"B vitamins are safe, but they were not, statistically, significantly more effective than placebo in preventing major vascular events among stroke and TIA [transient ischemic attack] patients," said lead researcher Dr. Graeme J. Hankey, head of the stroke unit at Royal Perth Hospital in Western Australia. "B vitamins have not been proven to have a role in secondary stroke prevention."
The report is published in the Aug. 4 online edition of The Lancet Neurology, and will appear in the September print issue of the journal.
For the study, Hankey and his colleagues in the Vitamins to Prevent Stroke (VITATOPS) trial tested whether lowering homocysteine with a combination of folic acid, vitamin B6 and vitamin B12 would lower the risk of a second stroke or heart attack in patients who had a recent stroke or transient ischemic attack.
In the trial, 8,164 patients were randomly assigned to daily doses of either B vitamins or a placebo in addition to standard care.
Over 3.4 years of follow-up, the researchers found the vitamins were no more effective than placebo. In all, 15% of the people taking B vitamins had a second stroke, heart attack or died, compared with 17% of those receiving placebo. B vitamins did, however, lower homocysteine levels.
People taking the vitamins had no adverse reactions and the vitamins were well-tolerated, the researchers noted.
Despite these findings, Hankey isn't sure that B vitamins don't work. "Our study may well have been underpowered statistically," he said.
Had the trial gone on longer, a "significant treatment effect may have emerged, and has thus been missed in our study," Hankey added.
"I don't think it is the end of the road for B vitamins in stroke prevention. We need to see the effect of B vitamins in the three other ongoing trials, particularly in patients who have been treated for several years, and particularly in patients with stroke caused by small vessel intracranial disease," he added.
Dr. Larry B. Goldstein, director of the Duke Stroke Center at Duke University Medical Center, agreed 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.
"High homocysteine is associated with both stroke and coronary heart disease. Homocysteine can be lowered with B-complex vitamin supplements, but whether doing so lowers the risk of vascular events is uncertain," Goldstein said.
Earlier studies found no benefit of homocysteine lowering in subjects with coronary heart disease or renal failure. "The VISP trial, conducted in North America, found no benefit of B-vitamin treatment in subjects with prior stroke, but had several important methodological limitations," Goldstein added.
This new report also finds no benefit of treatment with B-complex vitamins in patients with stroke or TIA, but the adverse event rates in both the treatment and placebo groups were lower than anticipated, he pointed out.
"A benefit by as much as an 18% reduction in risk remains possible," Goldstein said. "Treatment with B vitamins appeared safe, and the results of other ongoing trials should help more definitively answer the question."
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