Adding folic acid to their diet can cut a person's stroke risk by a fifth, cumulative evidence suggests.
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.