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Korean researchers have discovered that the effect of air pollutants on mortality risk in patients with idiopathic pulmonary fibrosis (IPF) is independent of their smoking status, according to a study published in the European Respiratory Journal. 

The authors of this study previously published a paper on the effect of air pollutants in residential areas on the mortality risk of patients with IPF. However, since smoking releases nitrogen dioxide (NO2 ) and other potentially harmful particulate matter, they decided to continue their investigation into whether smoking plays a significant role in increasing the risk of mortality in patients with IPF. 

“Thus, we stratified all patients into ever- and nonsmokers according to their smoking status and analyzed the effect of air pollutants on mortality risk in these patients using our health analysis models that included different sets of confounders,” the authors of the study wrote. 


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Among the 1114 IPF patients recruited, 846 (75.9%) patients were classified as “ever-smokers” and 268 (24.1%) were classified as “nonsmokers.” The researchers found that ever-smokers were mostly male, had a higher baseline forced vital capacity, and were treated less frequently with anti-inflammatory drugs compared to nonsmokers. However, there was no significant difference between the groups in terms of age, body mass index, diffusing capacity for carbon monoxide, and annual concentrations of NO2  and particulate matter.

Importantly, there was no significant difference in the median survival period between ever-smokers and nonsmokers (4.3 years vs 3.9 years, respectively; P =.815), and the hazard ratios of mortality for NO2 were relatively similar.  

The authors of this study acknowledged that the effects of smoking on the prognosis of patients with IPF remain controversial. Some studies have demonstrated that smoking increases the risk of developing IPF, while other studies have indicated that smokers have higher survival rates and lower frequencies of acute exacerbations than nonsmokers.

Researchers hypothesized that this could be due to the “healthy smoker” effect — a scenario in which diseases in smokers are diagnosed earlier due to more frequent hospital visits for smoking-related health issues. Alternatively, smoking also could have helped them develop more resistance in their lungs against acute exacerbations.  

Reference

Yoon HY, Kim SY, Kim OJ, Song JW. The role of cigarette smoking-derived pollutants in the risk of mortality in idiopathic pulmonary fibrosis. Eur Respir J. Published online August 12, 2021. doi:10.1183/13993003.01739-2021