The finding comes from the Heart Outcomes Prevention Evaluation 2 trial of more than 5,500 men and women with heart disease. Participants were assigned to a daily regimen of either B vitamins or placebo pills for five years.
Results showed that people who took the vitamins were 25% less likely to suffer a stroke over the study period than those who took placebo.
But taking vitamins did not have any effect on the severity of stroke or any associated disabilities, says researcher Gustavo Saposnik, MD, of the University of Toronto.
He presented the findings at the International Stroke Conference 2009.
B Vitamins Lower Homocysteine
B vitamins lower blood levels of a compound called homocysteine. The risk of heart disease and stroke is increased when a person has high blood levels of homocysteine, so it follows that taking B vitamins to lower homocysteine levels would improve outcomes.
But until now, researchers have had little success trying to show that.
Study after study has failed to show that B vitamins prevent heart disease or stroke, says ASA spokesman Larry B. Goldstein, MD, director of the Duke Stroke Center at Duke University, in Durham, N.C.
"We need to sift through all the studies and try to figure out why the results are conflicting," he tells WebMD. Until then, Goldstein does not recommend taking vitamins to prevent cardiovascular disease.
Saposnik says he thinks his study is the first to "use an adequate dose" of vitamin B12 to lower homocysteine and stroke levels. The daily vitamin regimen in the new study involved 2.5 milligrams of folic acid, 50 milligrams of vitamin B6, and 1 milligram of vitamin B12 -- far more than most people get in their diets.
Still, Saposnik agrees with Goldstein that further study is needed before any firm conclusions can be drawn.
B Vitamins vs. Second Stroke
Also at the meeting, University of California, Los Angeles, researchers reported that taking B-complex vitamins as directed by your doctor may help lower the risk of a second stroke.
The study involved 3,353 people who had suffered a stroke. The researchers added high- or low-dose B vitamins -- folate, vitamin B12, and vitamin B6 -- to state-of-the-art medical care for two years.
Researchers collected demographic, clinical, and laboratory data when they entered the study and at follow-up visits six, 12, and 24 months later.
Previously reported findings from the trial were disappointing, suggesting that the B vitamins did not lower the risk of recurrent stroke. But this time, researchers looked at what happened when people actually took their medication.
First, they divided the participants into two groups: Those who took their vitamins as prescribed at least 80% of the time, and those who took them less frequently.
Results showed that people who stuck with the program were much less likely to suffer a second stroke, have a heart attack, or die: Only 13% did vs. 20% of the people who didn't follow through.
Goldstein says that may be because people who take the medication as directed are more likely to have other healthful characteristics: They may exercise more and eat a healthier diet, for example.