The latest data suggest an association between living in a disadvantaged neighborhood and developing brain atrophy, or experiencing a decrease in the number of brain cells or connections over time. Neighborhood disadvantage functions as a social determinant of health, reflecting the education, income, employment, and quality of housing within a particular geographic area. As brain atrophy typically predisposes individuals to dementia and cognitive decline, this finding has significant implications for protecting cognitive function as individuals age.
Impact of Neighborhood on Neurological Health
Examining the impact of neighborhood socioeconomic disadvantage on brain volume in a cognitively unimpaired population, researchers conducted a study of over 950 individuals without a history of cognitive impairment in Wisconsin. In their cross-sectional study, the research team evaluated participants living in the most socioeconomically disadvantaged neighborhoods using data from the Wisconsin Registry for Alzheimer’s Prevention and the Wisconsin Alzheimer’s Disease Research Center to assess T1-weighted structural MRI scans.
At the beginning of the trial, participants were not cognitively impaired based on the National Institute on Aging-Alzheimer’s Association diagnostic criteria, however, the cohort was enriched for Alzheimer’s disease risk based on a family history of dementia.
Led by Amy J.H. Kind, MD, PhD from the University of Wisconsin, researchers calculated total hippocampal volume by combining both left and right measurements and based total brain tissue volume measures on total white and gray matter volumes. Additionally, they computed both the Area Deprivation Index – a geospatially determined index of neighborhood-level disadvantage – and cardiovascular disease risk indices for each participant. Linear regression models were used to test the relationships between neighborhood disadvantage and hippocampal and total brain tissue volume – as assessed by magnetic resonance imaging.
Neighborhood Disadvantage Linked to Loss of Brain Volume
Earlier this year, the team published their findings online in JAMA Neurology which revealed that living in socioeconomically disadvantaged neighborhoods was associated with markedly decreased hippocampal and total brain tissue volume. Other middle-aged and older adults who lived in areas with lesser disadvantages experienced comparatively lower risks of both neurological outcomes. Researchers found that individuals living in the most disadvantaged neighborhoods experienced a mean of 7 years of age-related hippocampal atrophy.
Furthermore, they also noted that men living in these neighborhoods experienced a higher risk for brain atrophy than women, although the reasons for this correlation remain unknown.
Cardiovascular risk was found to mediate the association in the case of total cerebral volume, indicating that neighborhood-level disadvantage may be associated with the two neurological outcomes via distinct biological pathways.
However, investigators acknowledged potential limitations of the trial which included the “enriched risk study cohort” – including older participants and those with a family history of dementia. They note that this population “might be particularly vulnerable to the deleterious effects of neighborhood-level disadvantage on the hippocampus.” In addition, the study’s findings reveal associations and not causality due to its cross-sectional, observational nature and require further validation.
Different from the implications of individual-level socioeconomic status on neurological function, this is the first study to reveal a robust association between neighborhood-level disadvantage and hippocampal volume, according to researchers. The latest findings indicate that neighborhood disadvantage may be associated with brain tissue volume throughout the aging process even in the absence of clinical cognitive impairment.
These results may suggest new population markers to leverage in future research studies; neighborhood-level disadvantage could be considered in clinical decision-making or used to guide public health efforts that support healthy brain aging in such geographic areas.
