Eating fish at least once a week is good for the brain, slowing age-related mental decline by the equivalent of three to four years, a study suggests.

The research adds to the growing evidence that a fish-rich diet helps keep the mind sharp. Previous studies found that people who ate fish lowered their risk of Alzheimer's disease and stroke. Fish such as salmon and tuna that are rich in omega-3 fatty acids also have been shown to prevent heart disease.

For the new study, researchers measured how well 3,718 people did on simple tests, such as recalling details of a story. The participants, all Chicago residents 65 and older, took the tests three times over six years. They also filled out a questionnaire about what they ate that included 139 foods.

Read more about the effects of fish consumption on brain health at http://seattletimes.nwsource.com/html/health/2002553128_eatfish11.html