Silent brain infarcts -- only detectable by brain scans and found in about 20 percent of otherwise healthy elderly people -- can lead to dementia and stroke.

The study, published in the journal Neurology, found those eating tuna, salmon, mackerel, herring, sardines or anchovies three times or more per week had a nearly 26 percent lower risk of having brain infarcts, compared to people who did not eat fish regularly. Eating just one serving of this type of fish per week led to a 13 percent lower risk.

"While eating tuna and other types of fish seems to help protect against memory loss and stroke, these results were not found in people who regularly ate fried fish," study leader Jyrki Virtanen of the University of Kuopio in Finland said in a statement. "More research is needed as to why these types of fish may have protective effects, but the omega-3 fatty acids EPA and DHA would seem to have a major role."

For this study, 3,660 healthy people over age 65 underwent brain scans to detect silent brain infarcts. Five years later, 2,313 of the participants had brain scans again. The people involved in the study were also given questionnaires about fish in their diets.