That's the conclusion of an analysis of 15 studies, each of which asked people how frequently they ate fish, then followed them for between four and 30 years to see who suffered a stroke.

"I think overall, fish does provide a beneficial package of nutrients, in particular the omega-3s, that could explain this lower risk," said Dr. Dariush Mozaffarian, a Harvard School of Public Health epidemiologist whose research was included in the analysis.

"A lot of the evidence comes together suggesting that about two to three servings per week is enough to get the benefit."

Dr. Susanna Larsson and Dr. Nicola Orsini of the Karolinska Institutet in Stockholm, Sweden wrote in the journal Stroke that omega-3 fatty acids in fish might lower stroke risk through their positive effects on blood pressure and cholesterol.

Vitamin D, selenium and certain types of proteins in fish may also have stroke-related benefits, Mozaffarian added.

Data for the analysis came from close to 400,000 people age 30 to 103. The studies were done in the U.S., Europe, Japan and China.

Over anywhere from a few years to a few decades, about 9,400 people had a stroke. Eating three extra servings of fish each week was linked to a six-percent drop in stroke risk, which translates to one fewer stroke among a hundred people eating extra fish over a lifetime.

And the people in each study who ate the most fish were 12 percent less likely to have a stroke that those that ate the least.

Mozaffarian's own report separated the effects of different kinds of fish and found that people who ate more fried fish and fish sandwiches didn't get any stroke benefit, not surprisingly.

Fatty fish such as salmon and herring are especially high in omega-3s. The American Heart Association recommends at least two servings of fatty fish in particular each week.