Associations of short-term exposure to multiple air pollutants with hospital admissions for ischemic stroke in Lanzhou, China

Ambient air pollution has been increasingly recognized as a modifiable risk factor for cerebrovascular disease; however, evidence from heavily polluted valley cities remains limited. This study aimed to investigate the associations between short term exposure to six ambient air pollutants (PM 2.5 , PM 10 , SO 2 , NO 2 , O 3 8h, and CO) and daily hospital admissions for ischemic stroke (IS) in Lanzhou, a typical river valley city in northwestern China, and to conduct stratified analyses by gender, age, and season. Daily ischemic stroke hospital admissions from all public hospitals, concurrent air pollutant concentrations, and meteorological data in Lanzhou were obtained from January 1, 2016 to December 31, 2019. After controlled the confounding factors including long term trend of time, meteorological factors and day-of-week effect used an Quasi-Poisson regression combined with the distributed lag nonlinear mode, we quantitatively analysed the association between daily air pollution and daily admissions to hospitals for ischemic stroke, and explored whether there was a lag effect of air pollutants. And stratified analyses were performed by gender, age, and season. In addition, we fitted the exposure-response (E-R) curves and tested the stability of the associations adopting double pollutant models and changing freedom degrees in time. Over the four year study period, 53,489 ischemic stroke admissions were recorded, averaging 37 cases per day. In single pollutant models, each 10 µg/m³ increment in PM 2.5 (lag07), PM 10 (lag07), and SO 2 (lag05), and each 1 mg/m³ increment in CO (lag06) were associated with significantly elevated risks of ischemic stroke admission, with cumulative RRs of 1.038 (95% CI: 1.016–1.062), 1.005 (95% CI: 1.000–1.010), 1.059 (95% CI: 1.004–1.117), and 1.136 (95% CI: 1.032–1.249), respectively. Notably, NO 2 (lag7) and O 3 8h (lag07) exhibited inverse associations, with RRs of 0.986 (95% CI: 0.974–0.998) and 0.968 (95% CI: 0.948–0.988). In stratified analyses, higher point estimates for particulate matter were observed among individuals aged ≥ 75 years, while higher point estimates for several pollutants were observed among females and during the cold season. The exposure–response curves for PM 2.5 , PM 10 , and CO showed approximately linear associations without apparent thresholds within the observed exposure range. This study extends previous evidence from Lanzhou by examining ischemic stroke specific admissions during a later study period and evaluating a broader range of air pollutants. Positive associations were observed for PM 2.5 , PM 10 , SO 2 , and CO. Stratified analyses showed variations in point estimates across gender, age, and season subgroups. These findings may inform local air quality interventions and early warning strategies to reduce pollution related cerebrovascular risks, particularly during periods of high pollution.