Long-term exposure to ambient air pollution and respiratory disease mortality in Shenyang, China: a 12-year population-based retrospective cohort study.

BACKGROUND In China, both the levels and patterns of outdoor air pollution have altered dramatically with the rapid economic development and urbanization over the past two decades. However, few studies have investigated the association of outdoor air pollution with respiratory mortality, especially in the high pollution range. OBJECTIVE We conducted a retrospective cohort study of 9,941 residents aged ≥35 years old in Shenyang, China, to examine the association between outdoor air pollutants [particulate matter <10 µm in aerodynamic diameter (PM(10)), sulfur dioxide (SO(2)) and nitrogen dioxide (NO(2))] and mortality using 12 years of data. METHODS We applied extended Cox proportional hazards modeling with time-dependent covariates to respiratory mortality. Analyses were also stratified by age, sex, educational level, smoking status, personal income, occupational exposure and body mass index (BMI) to examine the association of air pollution with mortality. RESULTS We found significant associations between PM(10) and NO(2) levels and respiratory disease mortality. Our analysis found a relative risk of 1.67 [95% confidence interval (CI) 1.60-1.74] and 2.97 (95% CI 2.69-3.27) for respiratory mortality per 10 µg/m(3) increase in PM(10) and NO(2), respectively. The effects of air pollution were more apparent in women than in men. Age, sex, educational level, smoking status, personal income, occupational exposure, BMI and exercise frequency influenced the relationship between outdoor PM(10) and NO(2) and mortality. For SO(2), only smoking, little regular exercise and BMI above 18.5 influenced the relationship with mortality. CONCLUSION These data contribute to the scientific literature on the long-term effects of air pollution for the high-exposure settings typical in developing countries.