Heterogeneous associations of cumulative heat exposure with cognitive decline among older Japanese adults

INTRODUCTION: We investigated heterogeneity in the association between cumulative heat exposure and cognitive decline among older Japanese adults. METHODS: We analyzed 33,877 adults aged ≥ 65 years from a nationwide cohort (2010-2023) linked with long-term care insurance data. Cumulative heat exposure was indexed using population-weighted wet-bulb globe temperature. Generalized random forests estimated the average and conditional treatment effects. Heterogeneity was decomposed using permutation importance, excess CATE analysis, and UpSet plot analyses. RESULTS: During a 12-year follow-up, 25.3% developed cognitive decline. Heat exposure increased incidence by 12.17 cases per 1000 person-years (95% confidence interval [CI]: 2.54-21.62). Vulnerability profiles differed by age: among adults aged 65-74 years, multidimensional social and health constraints predominated; among those aged ≥ 75 years, functional decline and relational depletion dominated. DISCUSSION: Age-specific vulnerability profiles provide a foundation for precision public health: multidomain interventions for adults aged 65-74 years and proactive social outreach for those aged ≥ 75 years.