Short-term effects of particulate air pollution on male smokers and never-smokers

Numerous studies have shown that ambient air pollution and smoking are both associated with increased mortality, but until now there has been little evidence as to whether the effects of these 2 factors combined are greater than the sum of their individual effects. We assessed whether smokers are subject to additional mortality risk from air pollution relative to never-smokers.

This study included 10,833 Chinese men in Hong Kong who died at the age of 30 or above during the period 1 January to 31 December 1998. Relatives who registered for deceased persons were interviewed about the deceased's smoking history and other personal lifestyle factors about 10 years before death. Poisson regression for daily number of deaths was fitted to estimate excess risks per 10 microg/m increase in particulate matter with aerodynamic diameter <10 microm (PM10) in male smokers and never-smokers in stratified data, and additional excess risk for smokers relative to never-smokers in combined data.

In smokers there was a significant excess risk associated with PM10 for all natural causes and cardio-respiratory diseases for men age 30 years or older and men 65 or older. For all natural causes, greater excess risk associated with PM10 was observed for smokers relative to never-smokers: 1.9% (95% confidence interval = 0.3% to 3.6%) in men age 30 and older and 2.3% (0.4% to 4.3%) in those age 65 and older.

Ambient particulate air pollution is associated with greater excess mortality in male smokers compared with never-smokers.