Neighborhood greenspace and brain imaging outcomes in older adults without dementia from three US Alzheimer's Disease Research Centers.

Although mounting evidence supports that neighborhood greenspaces (e.g., trees and parks) may benefit cognitive health in older age, fewer studies have investigated benefits to brain health measured via magnetic resonance imaging (MRI). We used data on 892 older adults without dementia from three Alzheimer's Disease Research Centers, examining whether neighborhood greenspace (i.e., greenness and percentage park space) is associated with white matter hyperintensity (WMH) and hippocampal volumes from MRI. We also examined whether associations varied by sex, racial group, urbanicity, or apolipoprotein E genotype (genetic risk factor for Alzheimer's disease). Linear regression models that accounted for neighborhood clustering controlled for demographics, research center, cognitive function, neighborhood deprivation, and comorbidities (e.g., hypertension, diabetes, obesity). Interaction terms (e.g., greenness×sex) were added to the models to evaluate potential effect modification. Living in greener neighborhoods was associated with fewer WMH and greater hippocampal volume in the overall sample. In stratified analyses, the beneficial greenness-WMH association was restricted to Black (not White) participants (i.e., significant interaction). In contrast, an adverse association between park space and lower hippocampal volumes was detected among Black (not White) participants (i.e., significant interaction). Overall, this study suggests associations between living in neighborhoods with more greenspace and MRI biomarkers of lower cerebrovascular and dementia risk, although results were mixed for Black individuals. Our findings need replication in other cohorts that are ethnoracially diverse and that represent different geographic regions, and future studies are needed explain the counterintuitive associations between park space and hippocampal volume among Black older adults.