Air pollution, lung function and mortality: survival and mediation analyses in UK Biobank

Background Air pollution is associated with lower lung function, and both are associated with premature mortality and cardiovascular disease (CVD). Evidence remains scarce on the potential mediating effect of impaired lung function on the association between air pollution and mortality or CVD.

Methods We used data from UK Biobank (N∼200 000) with 8-year follow-up to mortality and incident CVD. Exposures to PM10, PM2.5, and NO2 were assessed by land-use regression modelling. Lung function [forced expiratory volume in 1-second (FEV1), Forced Vital Capacity (FVC), and their ratio] was measured between 2006–2010 and transformed to Global Lung Function Initiative z-scores. Adjusted Cox proportional hazards and causal proportional hazards mediation analysis models were fitted, stratified by smoking status.

Results Lower FEV1 and FVC were associated with all-cause and CVD mortality, and incident CVD, with larger estimates in ever- than never-smokers: (all-cause mortality Hazard Ratio (HR) per decrease FEV1 GLI z-score, ever-smokers: 1.29 [95%CI:1.24–1.34], never-smokers: HR 1.16 [95%CI:1.12–1.21]). Long-term exposure to PM2.5 or NO2 was associated with incident CVD, with similar effect sizes for ever and never-smokers. Mediated proportions of the air pollution—all-cause mortality estimates driven by FEV1 were 18% [95%CI:2%-33%] for PM2.5, and 27% [95%CI:3%-51%] for NO2. Corresponding mediated proportions for incident CVD were 9% [95%CI:4%-13%] for PM2.5 and 16% [95%CI:6%-25%] for NO2.

Conclusions Lung function may mediate a modest proportion of associations between air pollution on mortality and CVD outcomes. Results likely reflect the extent of either shared mechanisms or direct effects relating to lower lung function caused by air pollution.