Study author James V. Pottala of the University of South Dakota in Sioux Falls and Health Diagnostic Laboratory, Inc., in Richmond, Va., and colleagues tested the levels of omega-3 fatty acids EPA and DHA in red blood cells in 1,111 women who were part of the Women's Health Initiative Memory Study.
Eight years later, when the women were an average age of 78, magnetic resonance imaging scans were taken to measure their brain volume.
Shrinking brain volume is a sign of Alzheimer's disease as well as normal aging, Pottala said.
The study, published in the online issue of Neurology, found those with higher levels of omega-3s had larger total brain volumes eight years later, while those with twice as high levels of fatty acids had a 0.7 percent larger brain volume.
Those with higher levels of omega-3s also had a 2.7 percent larger volume in the hippocampus area of the brain, which plays an important role in memory. In Alzheimer's disease, the hippocampus begins to atrophy even before symptoms appear, the study said.
"These higher levels of fatty acids can be achieved through diet and the use of supplements, and the results suggest that the effect on brain volume is the equivalent of delaying the normal loss of brain cells that comes with aging by one to two years," Pottala said in a statement.