Characteristics and prognosis of never smokers with asthma in the general population

Abstract

Background: Asthma is associated with complications, cardiovascular comorbidities, and higher mortality in some individuals.

Objective: We tested the hypothesis that in individuals with asthma, never smokers have different characteristics and better prognosis than smokers.

Methods: Among 94,079 individuals aged 20-100 years from the Copenhagen General Population Study 5,691 had self-reported asthma. We examined respiratory symptoms, lung function, and levels of biomarkers in the systemic circulation. We assessed prospectively risk of exacerbations of asthma and COPD, pneumonias, lung cancer, ischemic heart disease(IHD), ischemic stroke(IS), and all-cause mortality.

Results: Compared to never smokers without asthma, individuals with asthma had more respiratory symptoms and airflow limitation, and higher levels of inflammatory and allergic biomarkers. Among individuals with asthma compared to never smokers without asthma, hazard ratios(HRs) for asthma exacerbations were 11(95% confidence interval:5.8-22) in never smokers,13(6.2-29) in former, and 18(8.2-39) in current smokers. Corresponding HRs for COPD exacerbations were 8.9(2.1-38), 23(8.8-58), and 36(12-105), for pneumonias 1.5(0.9-2.2), 1.6(1.0-2.4), and 2.4(1.6-3.7), for lung cancer 0.6(0.1-5.1), 4.0(1.3-12), and 13(4.3-41), for IHD 1.2(0.9-1.6), 1.5(1.2-2.0), and 2.0(1.4-2.9), for IS 1.4(0.9-2.1), 1.2(0.8-1.9), and 3.0(1.7-5.3), and for all-cause mortality 0.9(0.6-1.3), 1.5(1.1-2.0), and 2.7(1.9-3.7).

Conclusions: Never smokers with asthma were different with increased risk of exacerbations of asthma and COPD, but not pneumonias, lung cancer, cardiovascular comorbidities, or all-cause mortality. Smoking was the main explanation of poor prognosis in asthma.