Effect of built environment on the association between nighttime heat exposure and mortality in stroke patients: A case-crossover study in Shandong Province, China

BACKGROUND: Short-term exposure to extreme heat has been increasingly linked to cardiovascular mortality. However, limited evidence exists regarding the specific impact of nocturnal heat exposure on mortality among stroke patients, and the heterogeneity across residential contexts has not been fully examined. METHODS: Utilizing daily time-series mortality data for stroke patients in Shandong Province, China, we applied a time-stratified case-crossover design with inverse-probability weighting (IPW) to address time-varying confounding, estimating single-day and cumulative lag (0-7 days) associations between nocturnal heat exposure and mortality. Nocturnal heat was defined as the community-specific 95th percentile of mean nighttime temperature (19:00-07:00) during the warm season (May-October). Stratified analyses were conducted by age, sex, stroke subtype, and urban/rural residence. We further examined effect modification of this association by age, sex, stroke subtype, and urban/rural residence, as well as by built environment characteristics including greenness, artificial light at night (ALAN), residential land density, and building volume. RESULTS: Nocturnal heat exposure was associated with an elevated mortality risk among stroke patients, with the strongest associations at lag 1-2 days. The odds of all-cause, cardiovascular, and stroke-specific mortality increased by 17.6 % (OR 1.18, 95 % CI: 1.12-1.24), 22.1 % (OR 1.22, 95 % CI: 1.15-1.29), and 25.6 % (OR 1.26, 95 % CI: 1.17-1.35), respectively. Elevated risks were more evident among older adults (≥60 years), males, patients with hemorrhagic stroke, and rural residents. High greenness appeared to mitigate the mortality risk associated with nocturnal heat exposure, whereas other built environment factors showed limited modifying effects. CONCLUSIONS: Nocturnal heat exposure was associated with short-term increases in mortality among stroke patients. Neighborhood greenness appeared to mitigate these associations, suggesting that built -environment-based adaptation strategies may help protect vulnerable populations from climate-related health risks.