Impact of long-term exposure to ambient air pollution on the incidence of chronic obstructive pulmonary disease: A systematic review and meta-analysis

Background: It is well known that air pollution causes respiratory morbidity and mortality by inducing airway inflammation. However, whether long-term exposure to air pollution is associated with increased incidence of chronic obstructive pulmonary disease (COPD) is controversial. Methods: We conducted a systematic review and meta-analysis with a random-effects model to calculate the pooled risk estimates of COPD development per 10 μg/m3 increase in individual air pollutants. PubMed, Embase, and Cochrane Library were searched from the date of their inception to August 2019 to identify long-term (at least three years of observation) prospective longitudinal studies that reported the risk of COPD development due to exposure to air pollutants. The air pollutants studied included particulate matter (PM2.5 and PM10) and nitrogen dioxide (NO2). Results: Of the 436 studies identified, seven met our eligibility criteria. Among the seven studies, six, three, and five had data on PM2.5, PM10, and NO2, respectively. The meta-analysis results showed that a 10 μg/m3 increase in PM2.5 is associated with increased incidence of COPD (pooled HR 1.18, 95% CI 1.13–1.23). We also noted that a 10 μg/m3 increase in NO2 is marginally associated with increased incidence of COPD (pooled HR 1.07, 95% CI 1.00–1.16). PM10 seems to have no significant impact on the incidence of COPD (pooled HR 0.95, 95% CI 0.83–1.08), although the number of studies was too small. Meta-regression analysis found no significant effect modifiers. Conclusions: Long-term exposure to PM2.5 and NO2 can be associated with increased incidence of COPD.