BACKGROUND AND AIM - We evaluated the independent and joint-effects of air pollution, land/built environment characteristics and ambient temperature on all-cause mortality as part of the EXPANSE project.
METHOD - We collected data from six administrative cohorts covering Catalonia, Greece, the Netherlands, Rome, Sweden and Switzerland and three traditional cohorts in Sweden, the Netherlands and Germany. Participants were assigned exposure estimates for three environmental domains: air pollution [fine particulate matter (PM2.5), nitrogen dioxide (NO₂), black carbon (BC), warm season ozone (O3)], land/built environment [normalized difference vegetation index (NDVI), distance to water, impervious surfaces] and ambient temperature [the mean and standard deviation of warm and cool season temperature]. In each cohort, we applied Cox proportional hazard models adjusting for several individual and area-level variables. We evaluated the associations through single and multi-exposure models within and across domains. The joint effects were estimated using the Cumulative Risk Index (CRI). Cohort-specific Hazard Ratios (HRs) were combined using random-effects meta-analyses.
RESULTS - We observed >3.1 million deaths out of ~204 million person-years. In administrative cohorts, increased exposure to PM2.5, NO2 and BC was significantly associated with all-cause mortality [pooled HRs:1.054; 1.033, 1.032 respectively]. We observed adverse effects of increased impervious surface and mean season-specific temperature, and protective effects of increased O3, NDVI, distance to water and temperature variation on all-cause mortality. The CRI of air pollutants (PM2.5 or NO2) plus NDVI and mean warm season temperature, resulted in a stronger effect, compared to single-exposure HRs: [PM2.5 pooled HR:1.061, 95%C.I.(1.021-1.102) and NO2 pooled HR:1.041, 95%C.I.(1.025-1.057)].
CONCLUSIONS - The findings of our study not only support the independent adverse effects of long-term exposure to ambient air pollution and protective effects of greenness, but also highlight the increased effect when combined with other environmental exposures.