LOS ANGELES (KABC) -- Many doctors want patients to eat more seafood to benefit their brains, but some wonder if eating more fish means taking in more mercury that could actually hurt their brains.
To test the theory, Rush Medical Center researchers followed seniors living in retirement communities.
Participants had normal memory function when they entered the study and used detailed questionnaires to help them keep accurate logs of what they ate.
Each of the 286 seniors agreed to brain donation after they died.
"So we have a very comprehensive assessment of people's seafood consumption during their older age years and we can then relate seafood consumption to brain changes associated with dementia when they die," explained Dr. Martha Clare Morris with Rush University Medical Center.
Those changes include Alzheimer's disease warning signs such as plaques and tangles.
The study found eating seafood at least once a week decreased the occurrence of those changes, but the benefits were only seen in people with a genetic variant called APOE e4.
But APOE e4 is the largest known genetic risk factor for late onset Alzheimer's disease.
"The study provides another piece of evidence that seafood consumption may protect one against developing dementia," Morris said.
The report provided by the Journal of the American Medical Association also measured the potential effects of mercury on brain function.
"The increased level of seafood consumption did increase brain levels of mercury, but that the mercury didn't appear to have an impact on brain health," Morris stated.
While APOE e4 is the largest known risk factor for Alzheimer, not everyone with the genetic mutation gets the disease. Morris also said seafood consumption was only associated with less brain changes specific to Alzheimer's disease, not other forms of dementia.