Air pollution and ischemic stroke across socioeconomic groups in the Netherlands

Background: While air pollution is an established risk factor for ischemic stroke (IS), evidence on differential susceptibility across population subgroups remains limited. We investigated how associations between long-term air pollution exposure and IS risk varied across socioeconomic groups and urbanicity levels. Methods: This population based cohort study included 11.9 million adults ≥18 years with linked residential exposure data for PM2.5, PM10, and NO2. Socioeconomic position was assessed using individual-level and area-level indicators including welfare, education, employment history, and composite scores. Time-varying Cox proportional hazards models examined associations between annual average air pollution at home addresses and incident IS risk across socioeconomic and urbanicity groups. Results: During 2014-2019 follow-up, 152,868 incident IS cases were identified. Air pollution exposure was associated with increased IS risk for all pollutants: hazard ratios (HR) 1.07 [95% CI: 1.06; 1.08] per 5.0 μg/m³ PM2.5, 1.06 [1.05; 1.07] per 5.0 μg/m³ PM10, and 1.08 [1.08; 1.09] per 10 μg/m³ NO2. Associations were stronger in rural to moderately urbanised versus highly urbanised areas. Socioeconomic differences were most pronounced in rural to moderately urbanised areas, with consistently higher HRs among lower socioeconomic groups (e.g., lowest area-level education: HR 1.16 [1.08; 1.25] per 5.0 μg/m³ PM2.5), while disparities were minimal in highly urbanised areas. Conclusion: Air pollution's impact on IS risk varies significantly by socioeconomic position and urbanicity, with lower socioeconomic groups in rural to moderately urbanised areas showing increased vulnerability. These findings emphasize considering geographic and socioeconomic contexts in air pollution health assessments.