In this report, researchers conducted surveys of 14,960 adults age 65 or older living in China, India, Cuba, the Dominican Republic, Mexico, Peru or Venezuela.
The relationship between higher fish intake and lower dementia prevalence was consistent across all countries, with the exception of India.
For each increase in a person's reported fish intake - from never, to some days of the week, to most or all days of the week - the prevalence of dementia dipped by 19 percent.
The findings, published in the August 2009 issue of American Journal of Clinical Nutrition, support evidence from previous studies in developed nations.
Eating more fish was also linked to eating a higher-quality diet which contained more fruits, vegetables and whole grains.
Researchers believe the brain benefits probably come from the omega-3 fatty acids found most abundantly in oily fish like salmon, mackerel and albacore tuna.
Lab studies show that omega-3 fats have a number of properties that could help stave off dementia -- including actions that protect nerve cells, limit inflammation and help prevent the build-up of the amyloid proteins seen in the brains of Alzheimer's patients.
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