The findings of a unique new study are fishy … in a good way.
Many studies suggest that eating seafood helps protect against dementia.
On the other hand, seafood is a source of mercury, which can damage the brain, indirectly.
Mercury binds to selenium … an essential part of internal antioxidants that protect the brain from free radicals.
This explains why people who consume more mercury than selenium can suffer brain damage that harms thinking and memory (so-called cognitive impairment).
And it likely explains why adults and children who eat far more fish than most Americans do very well on developmental and academic tests.
Now, a study from Chicago's Rush University Medical Center – published in the Journal of the American Medical Association – reinforces the brain benefits of seafood.
Brain study is first of its kind
The new study is the first to compare both seafood consumption and brain levels of mercury to the risk for Alzheimer's disease and the presence of its physical signs in the brain (Morris MC et al. 2015).
The researchers recruited 544 older people who were free of dementia at the outset of the study, and followed them for an average of 4.5 years.
Participants' seafood intake was measured by multiple questionnaires completed in the years before their death.
The amounts of seafood reported by the participants ranged from low to moderate, and consisted mostly of the top 10 species consumed in the U.S. (including salmon and tuna), which have low to moderate levels of mercury.
The researchers performed brain autopsies on 286 people who died during the course of the study.
They measured the levels of mercury and selenium, and for abnormalities characteristic of Alzheimer's disease.
As study leader Martha Clare Morris, ScD, said, "Since mercury is a known neurotoxin, we wanted to determine whether brain mercury levels are correlated with brain neuropathologies.”
Fish-rich diets linked to lower dementia risk
The results of the brain autopsies fit with previous studies linking seafood-rich diets to reduced dementia risk.
The results of the autopsies linked higher seafood consumption to lower risk for Alzheimer's disease ... despite increased mercury levels.
The autopsies also linked higher seafood intakes to lower risk for two signs associated with Alzheimer's disease: amyloid "plaque” and brain-cell "tangles”.
It's important to note that the relatively large number of brains analyzed lowered the likelihood that the findings were due to chance.
Few participants took fish oil routinely, so the researchers couldn't draw any clear conclusions about its possible value for preventing dementia.
Benefits limited to high-risk participants
The study results only found brain benefits in certain people.
Fewer signs of Alzheimer's were seen only in the brains of those who met two criteria:
- Ate more seafood than most of the study participants.
- Had a specific variation in an Alzheimer's related gene called APOE.
That gene variation – called APOE4 – raises the risk of Alzheimer's disease very substantially.
What do the results mean?
Diets rich in seafood don't guarantee you won't get Alzheimer's or other, less common forms of dementia.
But there's now ample evidence that it's smart to eat plenty of seafood, and take omega-3 fish oil as insurance.
Enjoying seafood two or more times a week may delay the onset of dementia, and/or reduce the severity of its symptoms.
And the available evidence suggests that you can do even better by getting plenty of exercise and filling your plate with antioxidant-rich plant foods.
Your best choices are colorful fruits and vegetables, extra virgin olive oil, green tea, extra-dark chocolate, and natural (non-alkalized) cocoa.
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