Folic acid supplements can reduce the risk of stroke by up to 30 percent, according to researchers.
B-vitamin is already recommended for women who have just got pregnant or are trying to conceive because it protects against birth defects.
A new study now suggests that folic acid, a nutrient known to reduce homocysteine levels in the blood, also improves the health of arteries.
The vitamin is known to lower levels of homocysteine in the blood, an amino acid believed to boost the danger of stroke, heart disease and deep vein thrombosis.
Scientists, led by Professor Xiaobin Wang, from Northwestern University in Chicago, US, combined together the Lancet review of eight folic acid trials, centering on stroke.
They found that folic acid supplementation reduced the risk of stroke by an average 18 percent.
More thorough examination showed that long periods of treatment lasting over 36 months could reduce the risk by 30 percent.
No big reduction was seen if homocysteine did not drop, supporting the idea that this protein may be a significant stroke risk factor.
Professor Wang's team recommended more research, among individuals with no history of stroke who are from regions without grain fortification, with longer follow-up - four years or longer.
"Some recent studies have suggested that folic acid has even wider health benefits such as lowering the risk of heart disease, bone disease and stroke. However, further work is needed to establish whether folic acid does or does not have these additional effects," the BBC quoted a spokeswoman for the Food Standards Agency, as saying.
Dr Cynthia Carlsson, of the University of Wisconsin School of Medicine and Public Health, agreed, saying: "Ongoing 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."