Taking regular supplements of folic acid can reduce the risk of stroke by 18 per cent or more, conclude authors of a study published in this week's edition of The Lancet.
Folic acid seems to lower the concentrations of homocysteine, an amino acid in the blood that is thought to increase the risk of stroke, as well as cardiovascular disease and deep vein thrombosis, when found in high amounts in the blood.
The authors caution that there remains controversy as to whether folic acid supplementation can lead to improved outcomes for other cardiovascular conditions.
A team led by Dr. Xiaobin Wang, of Children's Memorial Hospital and Northwestern University Feinberg School of Medicine in Chicago, conducted a meta-analysis of eight trials of folic acid that had stroke reported as one of the endpoints.
They found folic acid supplementation reduced the relative risk of stroke by an average of 18 per cent. An even greater reduction of risk - 29 per cent -- was seen when the treatment lasted over 36 months.
If the supplementation reduced the concentration of homocysteine in the blood by more than 20 per cent, there was a 23 per cent reduced risk of stroke. And if the patient had no previous history of stroke, there was a 25 per cent stroke risk reduction.
The study also found that in regions that did not already have fortified or partly fortified grains, folic acid supplementation decreased the risk of stroke by 25 per cent.
The authors and an accompanying commentary caution that more clinical studies need to be done. They also say more investigation is needed into the effect of folic acid alone versus folic acid in combination with other B vitamins.
"Although this meta-analysis helps clarify answers to some questions about the role of homocysteine lowering in CVD (cardiovascular disease) prevention, 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 CVD outcomes," writes Dr Cynthia Carlsson of the University of Wisconsin School of Medicine and Public Health.
