I've spoken before about how the presence or absence of the “Alzheimer's gene” may affect which lifestyle changes are beneficial for you. A new study has added to that idea with a finding that seafood consumption was associated with fewer signs of Alzheimer's-related pathology, but only among those with the APOEe4 gene.
Seafood consumption was also associated with increased mercury levels in the brain, with levels rising the more seafood was consumed. However, higher levels of mercury were not correlated with any neuropathologies.
Fish oil supplementation was not associated with any differences in neuropathology. However, higher levels of alpha-linolenic acid (an omega-3 fatty acid found in flaxseed, chia seeds, walnuts, etc) were associated with a reduced chance of cerebral infarctions.
The study involved 554 deceased participants (average age 89.9 years) from the long-running Memory and Aging Project (MAP) conducted by Rush University Medical Center. The participants had completed annual dietary questionnaires over a number of years. The brains of 286 participants were autopsied, to assess neuropathologies and mercury levels.
The average educational attainment of the participants was 14.6 years; 67% were women.
The finding tempers the evidence from many studies that eating fish reduces Alzheimer's risk. However, it is consistent with what I believe is becoming apparent: that there are different paths to Alzheimer's, and thus different factors involved in preventing it, depending on your own particular gene-environment attributes.
 . ASsociation of seafood consumption, brain mercury level, and apoe ε4 status with brain neuropathology in older adults. JAMA [Internet]. 2016 ;315(5):489 - 497. Available from: http://dx.doi.org/10.1001/jama.2015.19451