Alzheimer’s Risk Doesn’t Rise With Mercury Levels in Seafood, Study Reports

While there is abundant evidence that seafood consumption protects from the development of dementia, little is known about the effects of mercury — a heavy metal present in seafood — on the risk of Alzheimer’s disease. A new study shows that seafood mercury does not at all alter disease risk in older adults.

Mercury is a neurotoxic substance that accumulates in biological tissues and is particularly present in aquatic animals. In fact, seafood is the main source of human mercury exposure.

The research team, led by Martha Clare Morris at the Rush University Medical Center in Chicago, examined if seafood consumption was correlated to mercury levels in the brain and whether any of the factors — seafood consumption or brain mercury — could be associated with neuropathology. The team examined brain tissue from 286 diseased individuals from the Memory and Aging Project,  a clinical neuropathological cohort study. All participants had answered questions about the frequency of seafood intake in a food frequency questionnaire. The mean age at death was 90 years and the average time between questionnaire and death was 4.5 years.

Results, reported in the journal JAMA under the title “Association of Seafood Consumption, Brain Mercury Level, and APOE ε4 Status With Brain Neuropathology in Older Adults,“ showed that brain mercury increased with increased consumption of seafood, measured as the number of seafood meals per week. When the researchers adjusted the statistical models for age, sex, education, and total energy intake, they noticed that one or more seafood meals per week were correlated with less Alzheimer’s disease pathology in people who carried the apolipoprotein E Alzheimer’s risk gene. Genetically predisposed individuals who ate seafood had both a lower density of neuritic plaques, and less severe and widespread neurofibrillary tangles. But fish oil supplementation showed no correlation with the neuropathological markers investigated.

Although the heavy metal has been associated with negative effects on neurocognitive development, it does not seem to impact the aging brain. Despite higher mercury levels in seafood consumers, no association between the heavy metal and Alzheimer’s pathology could be found, indicating that the benefits of seafood consumption in elderly people outweigh any potential risks. The authors said that the findings might not apply to younger individuals or to other ethnic groups, since the study sample was composed of elderly, mainly white, non-Hispanic individuals.

“To our knowledge, this is the first study to report on the relationship between brain concentrations of mercury and brain neuropathology or diet. The finding of no deleterious correlations of mercury on the brain is supported by a number of case-control studies that found no difference between Alzheimer disease patients and controls in mercury concentrations in the brain, serum, or whole blood,” the authors said in a press release.