The study, to be reported in the 30 March issue of The Journal of Neuroscience, found that mice fed a diet rich in DHA had less beta-amyloid, a protein that causes plaques in the brains of Alzheimer's patients, than mice on a normal diet.
Total amyloid was cut by 70 per cent in mice on the DHA-rich diet compared with those on another diet, said the researchers, while brain plaques were reduced by 40.3 per cent.
"These results suggest that dietary DHA could be protective against beta-amyloid production, accumulation, and potential downstream toxicity," write the researchers from the University of California at Los Angeles.
People with a high intake of the fatty acid have been found to be at lower risk but there is as yet little evidence to support a direct benefit of consuming DHA on Alzheimer's prevention.
The findings support previous research into DHA's effect on this disease.
Alzheimer's disease, the leading cause of dementia in the elderly, afflicts an estimated 4.5 million people in the US alone.