Folic acid supplementation may reduce the risk of stroke by 18 percent or more, but it's not clear whether it boosts outcomes for other cardiovascular conditions, researchers say.

A study published last year in the journal Circulation found that there was a significant drop in stroke death rates in Canada and the United States after both countries mandated folic acid fortification of cereals and breads in 1998.

For the new research, a U.S. team reviewed eight studies of folic acid supplementation, which lowers concentrations of homocysteine in the blood. High homocysteine levels are believed to increase the risk of stroke, cardiovascular disease, and deep vein thrombosis.

Professor Xiaobin Wang, of Northwestern University Feinberg School of Medicine in Chicago, and colleagues found that folic acid supplementation reduced the risk of stroke by an average of 18 percent.

Even greater risk reduction were noted when treatment lasted more than 36 months (29 percent lower risk); when homocysteine levels were reduced by more than 20 percent (23 percent lower risk); or if a patient had no previous history of stroke (25 percent lower risk).

In regions that did not already have supplementation via fortified foods, the introduction of folic acid supplementation reduced stroke risk by 25 percent.

"Our meta-analysis provides coherent evidence that folic acid supplementation can reduce the risk of stroke in primary prevention," the study authors wrote.

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