Long-term air pollution exposure accelerates ageing-associated degradation of lung function

Abstract

Several longitudinal studies have associated ambient air pollution exposure with lung function, while cohort evidence was extremely sparse in low- and middle-income countries (LMICs) experiencing heavy air pollution. In this study, we sought to establish the concentration-response association between long-term exposures to fine particulate matter (PM2.5) and gaseous air pollutants (e.g., nitrogen dioxide [NO2] and ozone [O3]) and lung function in Chinese middle-aged and older adults. We conceived a nationwide longitudinal study from 2011 through 2015, by enrolling 13,614 participants aged 45 and above from 28 provincial regions across mainland of China. Lung function in each survey wave was measured as peak expiratory flow (PEF) repeatedly by well-trained interviewers using standardized devices. We assigned the exposures to ambient air pollutants (PM2.5, NO2 and O3) of participants according to their residential cities at baseline, via deriving monthly estimates from well-validated spatiotemporal datasets developed by machine learning methods. Possible exposure biases were examined through Monte Carlo simulation approach with 1000 random simulations of the residential addresses for each participant. The associations of long-term air pollution exposure with PEF and PEF z-score were assessed using mixed-effects linear models. We compared estimated effects of each pollutant with the effect of aging on lung function to elevate interpretability of the association magnitude. Subgroup analyses were conducted to identify potential effect modifiers. We evaluated totally 34,196 repeated measurements of lung function from 13,614 adults. Mean of age at survey was 60.8 years (standard deviation 9.4 years). An increase of 10-μg/m3 in annual PM2.5, NO2 and O3 exposure was respectively associated with a decline in PEF of 14.6 (95% confidence interval: 13.1–16.2) L/min, 21.7 (19.6–23.8) L/min, and 25.5 (20.6–30.4) L/min, which were equivalent to the effects of aging by 3.9–7.3 years and percent declines of 4.9–8.5%. We observed approximately linear relationships between PEF and PM2.5 and O3, while a reversely J-shaped NO2-PEF relation was identified with steeper drops below 30 μg/m3. Stratified analyses suggested significantly greater lung function impairment associated with ambient air pollutants in men, younger (<65), and less-educated adults. Our primary findings were robust to the sensitivity analyses based on Monte Carlo simulation approach with 1000 simulations, as well as adjustments for co-pollutant analyses. This study provided national evidence that long-term exposure to ambient PM2.5, NO2 and O3 may be independently associated with reduced lung function in Chinese middle-aged and older adults. Improvement of air quality may substantially offset the deterioration of lung function due to ageing in LMICs.