PhotoIf you are an aging Baby Boomer, should you be eating more fish?

There have been studies suggesting that fish oils are good for brain function and may delay or prevent dementia. At the same time, fish can contain mercury, picked up from the environment, and mercury is believed to contribute to cognitive impairment.

Researchers at Rush University Medical Center have studied the relationship between mercury and diseases associated with dementia. They report that as mercury levels rise with seafood consumption, there were no associations with harm to the brain.

Instead, they discovered that seafood consumption was associated with less Alzheimer's disease neuropathology, in spite of the increased mercury levels.

Helps people most at risk

However, the the protection associated with seafood was only seen in people with a common genotype (APOE-?4) that increases the risk of developing Alzheimer's disease. In other words, for people at risk of developing Alzheimer's disease, eating seafood made it less likely.

"Seafood consumption is promoted for its many health benefits even though it's contaminated by mercury," study leader Martha Clare Morris, said in a release. "Since mercury is a known neurotoxin, we wanted to determine whether seafood consumption is correlated with increased brain mercury levels in older adults, and also whether seafood consumption or brain mercury levels are correlated with brain neuropathologies."

The researchers conclude that seafood consumption was significantly correlated with less Alzheimer disease pathology. In particular, it was associated with lower density of amyloid plaques in the brain and less severe and widespread tangles within the neurons. Plaques and tangles are normally present in Alzheimer's patients.

Mercury's role in dementia

A 2010 German study, published on a National Institutes of Health (NIH) website, concluded that exposure to inorganic mercury led to “significant memory deficits.” Some autopsy studies found increased mercury levels in brain tissues of AD patients.

The issue, then, may be the extent of mercury levels found in seafood. The Rush University researchers say it's likely that the types of fish consumed by the study participants reflect the top 10 consumed species in the U.S., which have low to moderate levels of mercury.

How much seafood should you eat? A report by the Harvard School of Public Health notes that it is a controversial subject. The report suggests striking a healthy balance, with fish showing up on the menu once or twice a week.

If you want to know what kind of fish is best, has compiled a list of the best and the worst.

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