Nitrogen dioxide increases the risk of disease progression in idiopathic pulmonary fibrosis

Air pollution affects clinical course and prognosis of idiopathic pulmonary fibrosis (IPF). However, the effect of individual exposure to air pollutants on disease progression is unclear. We aimed to identify the effect of individual exposure to nitrogen dioxide (NO2 ) and particulate matter (aerodynamic diameter ≤ 10 μm [PM10 ]) on disease progression in patients with IPF.The serial lung function data of 946 IPF patients (mean age: 65.4 years, male: 80.9%) were analysed. Individual-level long-term exposures to NO2 and PM10 at the residential addresses of patients were estimated using a national-scale exposure prediction model, constructed based on air quality regulatory monitoring data. Progression was defined as a relative decline (≥10%) in forced vital capacity. Individual- and area-level covariates were adjusted in the primary analysis model.Overall, 547 patients (57.8%) experienced progression during a median follow-up of 1.0 year (interquartile range: 0.4-2.6 years). In the primary model, a 10-ppb increase in NO2 concentration was associated with a 10.5% increase in the risk of progression (hazard ratio [HR] = 1.105; 95% CI = 1.000-1.219) in patients with IPF. There was also an increasing trend of progression in patients with IPF according to the second to fourth quartiles of NO2 (Q2 [HR = 1.299; 95% CI = 0.972-1.735], Q3 [1.409; 1.001-1.984], Q4 [1.598; 1.106-2.310]) compared to the first quartile. We found no association between PM10 and progression in IPF patients.Our data suggest that increased individual exposure to NO2 can increase the risk of progression in patients with IPF.