Fish oil supplements might help high-risk seniors stave off Alzheimer’s disease, a new study finds.

Older people with a higher genetic risk of Alzheimer’s experienced slower breakdown of their brain’s nerve cells if they took fish oil capsules, researchers reported Aug. 1 in the journal JAMA Network Open.

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These people carry the APOE4 gene variant, which increases risk of Alzheimer’s and is associated with an earlier age of onset, according to the National Institute on Aging.

“The fact that neuronal integrity breakdown was slowed in people randomized to omega-3 treatment who are also at high risk for Alzheimer’s disease is remarkable, and warrants a larger clinical trial in more diverse populations in the future,” said researcher Gene Bowman, a neurology instructor with the McCance Center for Brain Health at Massachusetts General Hospital in Boston.

However, fish oil supplements did not benefit all seniors in general, researchers noted.

“Our findings showed that over three years, there was not a statistically significant difference between placebo and the group that took fish oil,” said researcher Dr. Lynne Shinto, a professor of neurology with the Oregon Health & Science University School of Medicine. “I don’t think it would be harmful, but I wouldn’t say you need to take fish oil to prevent dementia.”

For the study, researchers recruited 102 people ages 75 and older who had relatively low levels of omega-3 fatty acids, the beneficial ingredient in fish oil.

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Fish oil supplements are touted as a means of improving brain function in people with memory problems, researchers said in background notes.

Participants received MRI brain scans at the start of the study and after three years looking for white matter lesions in the brain.

All had relatively high levels of white matter lesions but were otherwise healthy, with no dementia. These lesions can inhibit the ability of blood vessels to feed brain cells, increasing a person’s future risk of dementia, researchers said.

Half the participants were asked to take daily fish oil supplements, and the other half took a soybean-based placebo.

The MRI scans found a slight reduction in the progression of white matter lesions among people who took fish oil, but not enough to be statistically significant, researchers said.

However, APOE4 carriers who took fish oil experienced a dramatic reduction in the breakdown of their brain cell integrity as soon as one year after starting on fish oil, compared to the placebo group.

“This is the first dementia prevention trial to use modern prevention tools, such as a blood test and brain scan, to identify not only people at high risk for dementia, but also those well-suited to receive a specific nutritional intervention,” Bowman said.