Folic acid may reduce risk of stroke, but safety unproven
Folic acid supplements may help reduce the risk of stroke, a review suggests, but the safety of the approach is not clear.
In Saturday's issue of the medical journal the Lancet, researchers in the U.S. reported the results of eight previous studies on folic acid and stroke. People who took the supplements reduced their risk of stroke by about 18 per cent.
Among a subgroup who took the supplements for at least three years, the risk of stroke fell by about 30 per cent.
"Our meta-analysis provides coherent evidence that folic acid supplementation can significantly reduce the risk of stroke in primary prevention," Prof. Xiaobin Wang of Children's Memorial Hospital in Chicago and his colleagues concluded.
The beneficial effects of the supplements were higher in countries such as China and Norway, where grains are not fortified, and in people without a history of stroke.
"The issue of folic acid supplementation alone versus folic acid in combination with other B vitamins, as well as optimum dosage, should also be carefully considered in future trials," the study's authors said in calling for research with longer followups of at least four years.
Whether folic acid supplements help prevent stroke and heart disease is controversial.
For example, when the American Heart Association released its new guidelines on prevention of heart disease and stroke in women in February, the group concluded folic acid supplements were worthless for preventing heart disease.
Active role or bystander?
In both heart disease and stroke, higher levels of the amino acid homocysteine are found in the blood, which may lead to damage to the lining of blood vessels. Folic acid lowers levels of homocysteine.
But it is not certain that high levels of homocysteine contribute to the risk of heart disease and stroke orare merely "an innocent bystander of other pathological processes," cautioned Dr. Cynthia Carlsson, of the University of Wisconsin School of Medicine and Public Health in a journal commentary.
Other studies suggested folic acid in combination with other B vitamins seemed to increase the risk of heart disease.
"Ongoing randomized trials are needed before we can conclude that the benefit of continued use of previously deemed 'safe' vitamin supplements outweighs the risk of other adverse [cardiovascular disease] outcomes," Carlsson concluded.
Folate is a B vitamin that the body uses to make healthy new cells. It is found naturally in leafy green vegetables such as spinach, citrus fruits, legumes such as lentils, and kidney beans. The synthetic version, folic acid, is used to fortify grain products such as white flour and paste, and is the form found in dietary supplements.
The Public Health Agency of Canada recommends all women who could become pregnant should take a multivitamin containing 0.4 mg of folic acid daily to reduce the risk of neural tube defects, in which the central nervous system of achild fails to develop fully.