Exposure to nitrogen dioxide and chronic obstructive pulmonary disease (COPD) in adults: a systematic review and...

Exposure to nitrogen dioxide (NO₂) has long been linked to elevated mortality and morbidity from epidemiological evidences. However, questions remain unclear whether NO₂ acts directly on human health or being an indicator of other ambient pollutants. In this study, random-effect meta-analyses were performed on examining exposure to nitrogen oxide (NO_x) and its association with chronic obstructive pulmonary disease (COPD). The overall relative risk (RR) of COPD risk related to a 10 μg/m³ increase in NO₂ exposure increased by 2.0%. The pooled effect on prevalence was 17% with an increase of 10 μg/m³ in NO₂ concentration, and 1.3% on hospital admissions, and 2.6% on mortality. The RR of COPD cases related to NO₂ long-term exposure was 2.5 and 1.4% in short-term exposure. The COPD effect related with a 10 μg/m³ increase in exposure to a general outdoor-sourced NO₂ was 1.7 and 17.8% to exposure to an exclusively traffic-sourced NO₂; importantly, we did observe the effect of NO₂ on COPD mortality with a large majority in lag0. Long-term traffic exerted more severe impairments on COPD prevalence than long-term or short-term outdoor effect; long-term mortality effect on COPD was serious in single model from this meta-analysis. Overall, our study reported consistent evidence of the potential positive association between NO₂ and COPD risk.