While numerous studies have touted the cardiovascular benefits of eating fish several times a week, the new research found a similar benefit from just occasional meals of seafood.
Men who ate about 3 to 5 ounces of fish one to three times a month were 43 percent less likely to have a stroke during 12 years of follow-up. Men who ate fish more often did not reduce their risk any further, suggesting that a small amount works just as well as a larger one, said co-author Dr. Ka He of Harvard's School of Public Health and colleagues.
Their findings appear in Wednesday's Journal of the American Medical Association.
A study in JAMA last year found that women who ate about 4 ounces of fish two to four times a week cut their stroke risk by 48 percent. The study found lower risk reductions in women who ate fish once a week or less.
Whether the new results would apply to women was unknown because none were studied.
The American Heart Association's dietary recommendations include two servings of fish a week.
The researchers in the Harvard study said the reasons for their findings were unclear.
Omega-3 fatty acids, found in most fish, have been shown to lower levels of blood fats linked to cardiovascular disease and to help keep blood from clotting.
The study involved risk reductions for ischemic, or clot-related strokes, the most common kind. The researchers noted that native Alaskans eat a lot of fish and have a high incidence of hemorrhagic, or bleeding, strokes.
That has raised concerns that while the anti-clotting effects of fish can decrease the risk of clot-related strokes, they can have the opposite effect on bleeding strokes.
The Harvard study found no significant link between fish consumption and bleeding strokes, but only 106 of the 608 strokes that occurred were the bleeding type. The researchers said more study is needed.
The study was funded by the National Institutes of Health.