By Harold L. Karpman, MD, FACC, FACP
Clinical Professor of Medicine, UCLA School of Medicine
Dr. Karpman reports no financial relationships relevant to this field of study.
SYNOPSIS: Although moderate seafood consumption was correlated with higher brain levels of mercury, these levels were not correlated with brain neuropathology.
SOURCE: Morris CM, Brockman J, Schneider JA, et al. Association of seafood consumption, brain mercury level, and APOE e4 status with brain neuropathology in older adults. JAMA 2016;315:489-497.
Numerous studies have found protective associations between seafood consumption and dementia.1-5 However, seafood is also a source of mercury, a neurotoxin that may impair neurocognitive development.6 Previous research shows selenium reduces mercury toxicity.7 Morris et al studied whether seafood consumption is correlated with increased brain mercury levels, the relationship of these mercury levels to selenium, and also whether seafood consumption or brain mercury levels are correlated with brain neural pathologies.8
Morris et al carefully analyzed autopsied cases of deceased participants in the Rush Memory and Aging Project (MAP) who died between November 2004 and November 2015 and who had completed a dietary assessment before death. The MAP study is an ongoing clinical, neuropathological cohort study of older adults that began in 1997 and included residents of retirement communities and subsidized housing in Chicago.9 The blood mercury levels of 286 autopsied brains of 544 deceased participants were positively correlated with the number of seafood meals they consumed per week. Seafood consumption was significantly correlated with less Alzheimer’s disease pathology, including lower density of neuritic plaques, less severe and widespread neurofibrillary tangles, and a lower frequency of neuropathologically defined Alzheimer’s disease — but only among apolipoprotein E (APOE e4) carriers.8 Fish oil supplementation had no statistically significant correlation with any neuropathologic marker. The authors concluded that higher brain concentrations of mercury were not significantly correlated with increased levels of brain neuropathology.
COMMENTARY
Morris et al derived their findings from a dated, largely non-Hispanic Caucasian cohort. As a result, these findings may not be generalizable to younger adults or other racial or ethnic groups.8 Other study limitations were the subjective measure of dietary intake and the observational study design. However, the results of this study suggest that although seafood consumption was correlated with higher brain levels of mercury, these levels were not correlated with brain neuropathology, and that from a clinical point of view, moderate seafood consumption was correlated with a lesser burden of brain Alzheimer’s disease neuropathology. This latter finding is reassuring. Ingested mercury accumulates in the body over decades. The absence of an increased risk of Alzheimer’s disease or dementia related to mercury in this study suggests patients can consume seafood without substantial concern of mercury contamination diminishing its possible cognitive benefit in older adults. Since eating fatty fish has been considered potentially beneficial against cognitive decline in at least a proportion of older adults, it appears from the study results that patients who consume fish generally should not be concerned about the effects of possible mercury contamination from eating fish.
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Morris CM, Brockman J, Schneider JA, et al. Association of seafood consumption, brain mercury level, and APOE e4 status with brain neuropathology in older adults. JAMA 2016;315:489-497.
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