Dr. Zaldy S. Tan, a member of the Easton Center for Alzheimer's Disease Research at the University of California, Los Angeles, said the study involved 1,575 dementia-free study subjects -- average age 67 -- who underwent brain scans and were given tests measuring mental function, body mass and omega-3 fatty acid levels in their red blood cells.
The study, published in the journal Neurology, found people with lower levels of omega-3 fatty acids -- found in fatty fish such as sardines or salmon -- have lower brain volumes, equivalent to about two years of structural brain aging.
Omega-3 fatty acids include the nutrients docosahexaenoic acid and eicosapentaenoic acid. Researchers found that those whose DHA levels were in the bottom 25 percent had lower brain volumes than those with higher DHA levels.
In addition, those whose levels of all omega-3 fatty acids were in the bottom 25 percent scored lower on tests of visual memory and executive function, including problem-solving, multi-tasking and abstract thinking, the study said.