Does air pollution contribute to urban–rural disparity in male lung cancer diseases in China?

It remains unknown whether exposure to ambient air pollution can be a mediator linking socioeconomic indicator to health outcome. The present study aims to examine the mediation effect of PM₂.₅ air pollution on the association between urban–rural division and the incidence (mortality) rate of male lung cancer. We performed a nationwide analysis in 353 counties (districts) of China between 2006 and 2015. A structural equation model was developed to determine the mediation effect of exposure to PM₂.₅. We also tested whether the findings of the mediation effect of exposure to PM₂.₅ are sensitive to the controls of smoking factors and additional air pollutant, and PM₂.₅ exposures with different lag structures. According to the results, we found that exposure to PM₂.₅ significantly mediated the association between urban–rural division and the incidence rate of male lung cancer. Specifically, there were significant associations between urban–rural division, exposure to PM₂.₅, and the incidence rate of male lung cancer, with PM₂.₅ exposure accounting for 29.80% of total urban–rural difference in incidence rates of male lung cancer. A similar pattern of results was observed for the mortality rate of male lung cancer. That is, there was a significant mediation effect by PM₂.₅ on the association of the mortality rate with urban–rural division. The findings of exposure to PM₂.₅ as a mediator were robust in the three sensitivity analyses. In conclusion, urban–rural difference in exposures to PM₂.₅ may be a potential factor that contributes to urban–rural disparity in male lung cancer diseases in China. The findings inform that air pollution management and control may be effective measures to alleviate the great difference in male lung cancer diseases between urban and rural areas in China.