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Majority of never-smokers with airflow limitation do not have asthma: the Copenhagen General Population Study
  1. Yunus Çolak1,2,3,4,
  2. Shoaib Afzal3,4,5,
  3. Børge G Nordestgaard3,4,5,
  4. Peter Lange2,3,4,5,6
  1. 1Department of Internal Medicine, Section of Respiratory Medicine, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark
  2. 2Department of Public Health, Section of Social Medicine, University of Copenhagen, Copenhagen, Denmark
  3. 3The Copenhagen General Population Study, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark
  4. 4Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
  5. 5Department of Clinical Biochemistry, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark
  6. 6Medical Unit, Respiratory Section, Hvidovre Hospital, Copenhagen University Hospital, Hvidovre, Denmark
  1. Correspondence to Professor Peter Lange, Professor and Consultant in Respiratory Medicine, Department of Public Health, Section of Social Medicine, University of Copenhagen, Øster Farimagsgade 5, PO Box 2099, Copenhagen K DK-1015, Denmark; Peter.Lange{at}


Background A substantial proportion of individuals with airflow limitation are never-smokers. However, whether never-smokers with airflow limitation have undiagnosed asthma is unknown. We hypothesised that the majority of never-smokers with respiratory symptoms and airflow limitation but without known asthma have undiagnosed asthma by comparing characteristics and prognosis in never-smokers with airflow limitation and asthma (NS+AFL+A) with never-smokers with airflow limitation but without asthma (NS+AFL−A).

Methods Among 94 079 participants aged 20–100 years from the general population, 39 102 (42%) were never-smokers. In this group, 13 719 (35%) reported to have respiratory symptoms of whom 1610 (12%) had airflow limitation. We investigated characteristics and risk of complications (asthma or COPD exacerbations, pneumonias and all-cause mortality) and comorbidities (lung cancer, ischaemic heart disease, myocardial infarction, deep venous thrombosis and PE) during 4.5 years median follow-up.

Results NS+AFL−A compared with NS+AFL+A reported less allergy and respiratory symptoms, and had higher FEV1 and lower levels of eosinophils and IgE in peripheral blood. NS+AFL+A had increased risk of asthma and COPD exacerbations, but not of pneumonias; adjusted HRs in NS+AFL+A compared with NS+AFL−A were 16 (95% CI 3.7 to 73) for asthma exacerbations and 15 (2.8 to 80) for COPD exacerbations. Still, NS+AFL−A had increased risk of COPD exacerbations and pneumonias, but not of asthma exacerbations; adjusted HRs in NS+AFL−A compared with never-smokers without airflow limitation or asthma (NS−AFL−A) were 7.7 (2.8 to 21) for COPD exacerbations and 1.7 (1.3 to 2.3) for pneumonias. Risk of comorbidities or all-cause mortality was not increased in NS+AFL−A or NS+AFL+A compared with NS−AFL−A.

Conclusions Majority of NS+AFL−A do not seem to have undiagnosed asthma and may instead have airflow limitation caused by other risk factors.

  • Asthma
  • Asthma Epidemiology
  • Asthma Mechanisms
  • Clinical Epidemiology
  • COPD epidemiology
  • COPD Exacerbations
  • Pneumonia
  • Smoking cessation
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