Chronic effects of low-level air pollution on cause-specific mortality among 30 million residents of Europe: meta-analysis of 7 European large administrative cohorts in the ELAPSE project

Abstract

Background Long-term exposure to air pollution has been related to cause-specific mortality. However, results vary across studies because of heterogeneities in exposure assessment and statistical analysis. In addition, there is uncertainty on the shape of the association at low concentrations. The multicentre Effects of Low-Level Air Pollution: A Study in Europe (ELAPSE) study collected data from multiple European cohorts using standardized protocols for exposure assessment and statistical analysis, with focus on the exposure-response functions at low concentrations. Methods We analysed data from seven large administrative cohorts: Norway, England, Denmark, the Netherlands, Belgium, Switzerland and Rome, Italy. Annual average concentrations of PM2.5, NO2, BC and O3 were centrally modelled for Europe by hybrid land use regression at 100-m spatial resolution. Within each cohort we applied Cox proportional hazard models with adjustment for area- and individual-level confounders. We evaluated associations with cause-specific mortality (natural, cardiovascular, respiratory and lung cancer). Flexible approaches were used to capture non-linearity in the air pollution-mortality association. Finally, cohort-specific results where pooled into a random-effects meta-analysis. Results We analysed data on 27,896,312 subjects and observed 3,257,837 deaths from natural causes. We found significant associations with NO2 and PM2.5, with pooled hazard ratios (HRs) 1.04 (95% CI: 1.02, 1.07) and 1.05 (1.02, 1.09) per increments of 10 μg/m3 and 5 μg/m3, respectively. Similar results were obtained for cardiovascular and respiratory mortality, while higher estimates were reported for lung cancer mortality: 1.09 (1.02, 1.16) and 1.08 (1.05, 1.12). Associations with natural mortality remained significant when the analyses were restricted to very low concentrations, i.e. HRs below the WHO guidelines for PM2.5 (10 μg/m3) and NO2 (40 μg/m3) were 1.05 (1.00, 1.11) and 1.05 (1.02, 1.07), respectively. Conclusions Long-term exposure to low levels of air pollutants was associated with natural, cardiovascular, respiratory and lung cancer mortality in seven large European cohorts.