Studies have linked low blood levels of a chemical lowered by folic acid to reduced rates of stroke. However, folic acid supplements don't seem to prevent strokes, according to a review of clinical trials involving more than 39,000 participants.
"We do not have evidence that would warrant boosting folic acid supplementation for stroke reduction," researcher Dr. Jeffrey Saver told Reuters Health.
Saver and colleagues at the UCLA Stroke Center in Los Angeles identified 13 well-designed clinical trials of folic acid and stroke. Participants in all the trials had been diagnosed with conditions such as kidney and heart disease, as well as stroke.
There were 784 strokes among 20,415 participants taking folic acid, compared to 791 strokes reported among 18,590 people who did not take the supplements.
The analysis, in the American Heart Association's journal Stroke, settles the question about whether folic acid supplementation leads to a major reduction in stroke, Saver said.
"The answer is 'no,'" Saver said.
Still, the researchers suggest more research into folic acid and stroke, particularly for men and those in the earliest stages of heart disease. Data from both of those groups suggested there might be an effect, although researchers could not determine whether or not that was due to chance.
Those potential benefits appeared in trials carried out in countries whose food supplies were not fortified with folic acid. In the U.S., the benefits of folic acid supplementation may have already been achieved through food fortification, Saver noted. In an effort to reduce the birth defect spina bifida, the U.S. Food and Drug Administration required the addition of folic acid to all enriched cereal-grain foods starting in 1998.
"Extra pills don't make that much additional difference," Saver said.