# Association of intrinsic capacity and neighborhood environment with dementia risk: an interaction and mediation analysis

## TL;DR

This study explores how personal health and neighborhood conditions together influence dementia risk, finding that both factors independently increase risk and that personal health partially explains the impact of poor neighborhoods.

## Contribution

The study reveals that intrinsic capacity partially mediates the relationship between neighborhood environments and dementia risk, offering new insights into combined individual and environmental risk factors.

## Key findings

- Each 1-point increase in intrinsic capacity impairment score raises dementia risk by 26%.
- Moderate- and high-risk neighborhoods independently increase dementia risk by 26% and 41%, respectively.
- Adverse neighborhood effects on dementia risk are partially explained by intrinsic capacity impairments.

## Abstract

While intrinsic capacity (IC) impairment and adverse neighborhood environments are established independent risk factors for dementia, their interaction effects and potential mediating pathways remain poorly understood. This study aimed to examine the independent, interactive, and mediating associations of IC, neighborhood environment, and dementia risk among middle-aged and older adults.

We analyzed data from 8,107 adults aged 50+ in the China Health and Retirement Longitudinal Study (2011–2020). IC was quantified using a composite impairment score encompassing locomotor, cognitive, sensory, psychological, and vitality domains. Neighborhood environment was classified by resource availability and social provisions (low risk; moderate risk; high risk). Cox proportional hazards models evaluated associations between IC, neighborhood environment, and dementia risk. The four-way decomposition model was used to examine the potential interaction and mediation effects of IC.

Over a median follow-up of 9 years, 909 incident dementia cases occurred. Adjusted analyses revealed dose-dependent relationships: each 1-point increase in IC impairment score elevated dementia risk by 26% (hazard ratio [HR] = 1.29, 95% confidence interval [CI]: 1.22–1.36). Compared with low-risk neighborhoods, moderate-risk (HR = 1.26, 95% CI: 1.08–1.47), and high-risk neighborhoods (HR = 1.41, 95% CI: 1.13–1.77) independently increased dementia risk. Four-way decomposition revealed the association between adverse neighborhood environments and increased dementia risk was partially explained by the pure mediation effect of IC, with no significant interaction-only/mediated interaction effects observed.

IC impairments and adverse neighborhood environments independently escalate dementia risk, with IC partially mediating the environmental effects. Integrating interventions targeting both individual capacity and community-level infrastructure may optimize dementia prevention strategies.