Adding folic acid to their diet can cut a person's stroke risk by a fifth, cumulative evidence suggests.
Folic acid may protect the brain
Food advisors have already recommended to ministers that the vitamin should be added to flour or bread.
This is to benefit pregnant women and those trying to conceive, by protecting the unborn child against birth defects.
The Lancet review of eight studies shows the benefits could be more widespread, but experts warn that this must be balanced against other risks.
An increase in folic acid can mask a vitamin B12 deficiency in older people.
This type of anaemia can cause serious health problems, like nerve damage.
Folate is a water-soluble B vitamin that occurs naturally in food. Folic acid is the synthetic form of folate that is found in supplements and added to fortified foods
Both folic acid and vitamin B12 are essential for good health and good levels can be achieved by eating a healthy, balanced diet.
Green vegetables are rich in folic acid or folate, while B12 is found in foods such as eggs and meat.
Yet 13 million people do not consume enough folate, according to the Food Standards Agency.
The current advice is that all adults consume 200 micrograms of folate per day, and that women who are pregnant or thinking of having a baby should take a daily 400 microgram supplement from the time they start trying for a baby until the 12th week of pregnancy.
Mandatory fortification of flour with folic acid is already in place in several countries, including the US, to help ensure this.
Experts have known for some time that folic acid appears to carry brain benefits.
It lowers the level of homocysteine, a blood protein linked both to heart disease and dementia.
Professor Xiaobin Wang, of the Children's Memorial Research Center in the US, and colleagues looked at available data on the effects of folic acid supplementation on stroke.
They found the vitamin reduced the relative risk of stroke by an average of 18%.
An even greater risk reduction - 30% - was seen when the treatment lasted more than 36 months, or if the individual had no past history of stroke - 25% less risk.
No big reduction was seen if homocysteine did not go down, supporting the idea that this protein may be an important 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.
A spokeswoman for the Food Standards Agency said: "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."
Dr Peter Coleman of The Stroke Association cautioned: "Supplementing the diet with folic acid may reduce the risk of stroke in certain individuals, but is not suitable for everybody, and could actually increase the risk of cardiovascular disease in some people.
"We urge people to consult with their doctors before taking any supplements or medication with a view to reducing their risk of stroke."