Neighborhood Social Environment and Dementia: The Mediating Role of Social Isolation.

Objectives: Despite the potential importance of the neighborhood social environment for cognitive health, the connection between neighborhood characteristics and dementia remains unclear. This study investigated the association between the prospective risk of dementia and three distinct aspects of neighborhood social environment: socioeconomic deprivation, disorder, and social cohesion. We also examined whether objective and subjective aspects of individual-level social isolation may function as mediators.

Methods: Leveraging data from the Health and Retirement Study (2006-2018; N = 9,251), we used Cox proportional hazards models to examine the association between time-to-dementia incidence and each neighborhood characteristic, adjusting for covariates and the propensity to self-select into disadvantaged neighborhoods. We used inverse odds weighting to decompose significant total effects of neighborhood characteristics into mediational effects of objective and subjective social isolation.

Results: The risk of dementia was associated with deprivation and disorder but not low cohesion. In deprived neighborhoods, individuals had an 18% increased risk of developing dementia (cause-specific hazard ratio [CHR] = 1.18, 95% CI: 1.02 to 1.38), and those in disordered areas had a 27% higher risk (CHR = 1.27, 95% CI: 1.03 to 1.59). 20% of the disorder's effects were mediated by subjective social isolation, while the mediational effects of objective isolation were nonsignificant. Deprivation's total effects were not partitioned into mediational effects given its nonsignificant associations with the mediators.

Discussion: Neighborhood deprivation and disorder may increase middle to older adults' risks of dementia. The disorder may adversely affect cognitive health through increasing loneliness. Our results suggest a clear need for dementia prevention targeting upstream neighborhood contexts, including the improvement of neighborhood conditions to foster social integration among residents.