Long-Term Exposure to Urban Air Pollution and Mortality in a Cohort of More than A Million Adults in Rome.

BACKGROUND: Few European studies have investigated the effects of long-term exposure to both fine particulate matter (PM2.5) and nitrogen dioxide (NO2) on mortality. OBJECTIVES: To analyze the association of exposure to NO2, PM2.5 and traffic indicators on cause-specific mortality; to evaluate the form of the concentration-response relationship. METHODS: We analyzed a population-based cohort enrolled at 2001 Census with 9 years of follow-up. We selected all 1,265,058 subjects, aged ≥ 30 years, who had been living in Rome for at least 5 years at baseline. Residential exposures included annual NO2 (from a land use regression model), annual PM2.5 (from a Eulerian dispersion model), traffic intensity and distance to roads with >10,000 vehicles/day. We used Cox regression models to estimate associations with cause-specific mortality adjusted for individual (sex, age, place of birth, residential history, marital status, education, occupation) and area (socioeconomic status, clustering) characteristics. RESULTS: Long-term exposures to both NO2 and PM2.5 were associated with an increase in non-accidental mortality (Hazard Ratio, HR=1.03; 95% CI: 1.02, 1.03 per 10 µg/m3NO2; HR = 1.04; 95% CI: 1.03, 1.05 per 10 µg/m3 PM2.5). The strongest association was found for ischemic heart diseases (IHD, HR = 1.10; 95% CI: 1.06, 1.13 per 10 µg/m3 PM2.5), followed by cardiovascular diseases and lung cancer. The only association showing some deviation from linearity was that between NO2 and IHD. In a bi-pollutant model, the estimated effect of NO2 on mortality was independent of PM2.5. CONCLUSIONS: This large study strongly supports an effect of long-term exposure to NO2 and PM2.5 on mortality, especially from cardiovascular causes. The results are relevant for the next European policy decisions regarding air quality.