Features of the Physical and Social Neighborhood Environment and Neighborhood-Level Alzheimer's Disease and Related Dementia in South Carolina

Background: Studies are increasingly examining the relationship between the neighborhood environment and cognitive decline; yet, few have investigated associations between multiple neighborhood features and Alzheimer's disease and related dementias (ADRD).

Objective: We investigated the relationship between neighborhood features and ADRD cumulative incidence from 2010 to 2014 in the South Carolina Alzheimer's Disease Registry (SCADR).

Methods: Diagnosed ADRD cases $\ge 50\text{years}$ of age were ascertained from the SCADR by ZIP code and census tract. Neighborhood features from multiple secondary sources included poverty, air pollution [particulate matter with a diameter of 2.5 micrometers or less (${\mathrm{PM}}_{2.5}$)], and rurality at the census-tract level and access to healthy food, recreation facilities, and diabetes screening at the county level. In addition to using Poisson generalized linear regression to estimate ADRD incident rate ratios (IRR) with 95% confidence intervals (CIs), we applied integrated nested Laplace approximations and stochastic partial differential equations (INLA-SPDE) to address disparate spatial scales. We estimated associations between neighborhood features and ADRD cumulative incidence.

Results: The average annual ADRD cumulative incidence was 690 per 100,000 people per census tract (95% CI: 660, 710). The analysis was limited to 98% of census tracts with a population $\ge 50\text{years}$ old (i.e., 1,081 of 1,103). The average percent of families living below the federal poverty line per census tract was 18.8%, and $\sim 20\%$ of census tracts were considered rural. The average percent of households with limited access to healthy food was 6.4%. In adjusted models, every ${5\mu g/m}^3$) increase of ${\mathrm{PM}}_{2.5}$ was associated with 65% higher ADRD cumulative incidence ($\text{IRR}=1.65$; 95% CI: 1.30, 2.09), where ${\mathrm{PM}}_{2.5}$ at or below $12{\mu g/m}^3$ is considered healthy. Compared to large urban census tracts, rural and small urban tracts had 10% ($\text{IRR}=1.10$; 95% CI: 1.00, 1.23) and 5% ($\text{IRR}=1.05$; 95% CI: 0.96, 1.16) higher ADRD, respectively. For every percent increase of the county population with limited access to healthy food, ADRD was 2% higher ($\text{IRR}=1.02$; 95% CI: 1.01, 1.04).

Conclusions: Neighborhood environment features, such as higher air pollution levels, were associated with higher neighborhood ADRD incidence. The INLA-SPDE method could have broad applicability to data collected across disparate spatial scales. https://doi.org/10.1289/EHP13183.