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All, Like we've seen for cardiovascular disease, eating fish can be a mixed blessing. The omega-3 fatty acids (DHA/EPA) are thought to be beneficial, particularly for brain function. But the mercury, PCBs and other contaminants that bioaccumulate in the fat of fish may also have harmful effects. This new study (thanks to Al Pater!) looks at the association between consumption of fish, plant omega-3s, brain mercury levels and Alzheimer's disease and brain mini-strokes. What they found is a bit nuanced, but worth thinking about. They gave 550 quite elderly but initially dementia-free people in several US nursing homes a yearly dietary questionnaire to measure their weekly intake of fish, DHA/EPA and the plant-derived omega-3 Alpha Linolenic Acid (ALA) until they died. Over an average follow-up of 4.5 years, 286 of the participates died (average age 89!). These folks' brains were autopsied to measure mercury levels and to look for physical signs of Alzheimer's disease (plaques and tangles) as well as brain injuries associated with other forms of dementia, in particular macroinfarctions and microinfarctions (i.e. strokes of various sizes). Here are the highlights of what they found: The more fish meals per week a subject consumed, the higher their brain mercury level (P < 0.02). There was no correlation between intake of ALA or DHA/EPA supplements and brain mercury level. For the majority of people (77%) who weren't carriers of the APOE4 allele that increases one's susceptibility to Alzheimer's disease, neither eating fish, dietary DHA/EPA nor consuming ALA had a significant effect (one way or the other) on the risk of Alzheimer's disease. For the minority (23%) of subjects who were APOE4 carriers, eating more fish and more dietary DHA/EPA was associated with a decreased risk of Alzheimer's disease markers (P < 0.04). Neither DHA/EPA supplements nor dietary ALA impacted Alzheimer's risk in these folks. Dietary ALA, but not fish or DHA/EPA, was associated with reduced prevalence of macroinfarctions (P < 0.03) and microinfarctions (P < 0.04) associated with non-Alzheimer's cognitive impairment, independent of APOE4 status. Those were the major, statistically significant findings. There is one more thing I noticed looking at the table below that appears interesting/suggestive for the majority of us who are lucky enough not have the APOE4 gene. The cells I've highlighted below represent the level of various markers of Alzheimer's disease for APOE4-negative folks. The red cells represent the level of Alzheimer's markers for people who ate the most fish (top red row), or the most dietary DHA/EPA (bottom red row). From the confidence intervals, you can see that none of them are individually significant. But also notice that all of them are positive, meaning there was a trend towards increased markers of Alzheimer's disease in APOE4-negative people who ate the most fish, especially fatty fish. In contrast, now look at the green cells, representing markers for Alzheimer's disease in APOE4-negative people who consumed the most plant-derived ALA. Notice these too are not individually significant, but all of them are negative, pointing towards a reduced risk of Alzheimer's disease with increasing ALA intake. From all this, my summary takeaway message from this study would be the following: For people with the APOE4 gene and therefore increased risk of Alzheimer's disease, eating fish is likely to reduce one's risk of Alzheimer's disease, despite increasing brain mercury levels For people without the APOE4 gene, fish consumption doesn't seem to reduce, and may even increase, one's risk of Alzheimer's disease For people without the APOE4 gene, plant-derived omega-3 ALA (e.g. from walnuts, olive oil, flax, chia) consumption may reduce one's risk of Alzheimer's disease For everyone, dietary ALA appears to reduce one's risk of brain markers for non-Alzheimer's cognitive impairment. Or more succinctly, ALA is likely to be good for everyone's brain health, and fish is likely to be good for the brain health of only the minority of people who carry the APOE4 allele. This seems like an illustration of a benefit of getting one's DNA sequenced with a company like 23andMe to determine whether one is a carrier of the APOE4 allele. --Dean ------------  JAMA. 2016 Feb 2;315(5):489-97. doi: 10.1001/jama.2015.19451. Association of Seafood Consumption, Brain Mercury Level, and APOE e4 Status With Brain Neuropathology in Older Adults. Morris MC, Brockman J, Schneider JA, Wang Y, Bennett DA, Tangney CC, van de Rest O. Full text: http://jama.jamanetwork.com.sci-hub.io/article.aspx?articleID=2484683 Abstract IMPORTANCE: Seafood consumption is promoted for its many health benefits even though its contamination by mercury, a known neurotoxin, is a growing concern. OBJECTIVE: To determine whether seafood consumption is correlated with increased brain mercury levels and also whether seafood consumption or brain mercury levels are correlated with brain neuropathologies. DESIGN, SETTING, AND PARTICIPANTS: Cross-sectional analyses of deceased participants in the Memory and Aging Project clinical neuropathological cohort study, 2004-2013. Participants resided in Chicago retirement communities and subsidized housing. The study included 286 autopsied brains of 554 deceased participants (51.6%). The mean (SD) age at death was 89.9 (6.1) years, 67% (193) were women, and the mean (SD) educational attainment was 14.6 (2.7) years. EXPOSURES: Seafood intake was first measured by a food frequency questionnaire at a mean of 4.5 years before death. MAIN OUTCOMES AND MEASURES: Dementia-related pathologies assessed were Alzheimer disease, Lewy bodies, and the number of macroinfarcts and microinfarcts. Dietary consumption of seafood and n-3 fatty acids was annually assessed by a food frequency questionnaire in the years before death. Tissue concentrations of mercury and selenium were measured using instrumental neutron activation analyses. RESULTS: Among the 286 autopsied brains of 544 participants, brain mercury levels were positively correlated with the number of seafood meals consumed per week (??=?0.16; P?=?.02). In models adjusted for age, sex, education, and total energy intake, seafood consumption (=?1 meal/week) was significantly correlated with less Alzheimer disease pathology including lower density of neuritic plaques (ß?=?-0.69 score units [95% CI, -1.34 to -0.04]), less severe and widespread neurofibrillary tangles (ß?=?-0.77 score units [95% CI, -1.52 to -0.02]), and lower neuropathologically defined Alzheimer disease (ß?=?-0.53 score units [95% CI, -0.96 to -0.10]) but only among apolipoprotein E (APOE e4) carriers. Higher intake levels of a-linolenic acid (18:3 n-3) were correlated with lower odds of cerebral macroinfarctions (odds ratio for tertiles 3 vs 1, 0.51 [95% CI, 0.27 to 0.94]). Fish oil supplementation had no statistically significant correlation with any neuropathologic marker. Higher brain concentrations of mercury were not significantly correlated with increased levels of brain neuropathology. CONCLUSIONS AND RELEVANCE: In cross-sectional analyses, moderate seafood consumption was correlated with lesser Alzheimer disease neuropathology. Although seafood consumption was also correlated with higher brain levels of mercury, these levels were not correlated with brain neuropathology. PMID: 26836731