Most experts recommend eating fish to protect heart and brain health. However, because of concerns about mercury toxicity, moderation is important.

One study questions prior guidance on the topic. Scientists at Rush University Medical Center in Chicago found that although older people who ate the most seafood had higher brain mercury levels, they didn’t suffer any ill effects from the mercury.

For participants who had a genetic risk for Alzheimer’s disease, their high fish consumption led to a lower risk for the disease.

The 544 volunteers completed questionnaires about their dietary habits four and a half years before their death, and half of them underwent brain autopsies. The researchers found that frequency of seafood meals eaten each week correlated with brain mercury levels.

The most frequent seafood eaters also had fewer brain plaques and tangles, which are the abnormal protein deposits characteristic of Alzheimer’s disease.

Volunteers with the APOE4 genetic risk who reported consuming more fish had fewer plaques and tangles than those who ate little or no fish.

Although fish consumption was linked to lower Alzheimer’s risk, use of fish oil supplements was not.