Characteristics of COPD in never-smokers and ever-smokers in the general population: results from the CanCOLD study

Thorax. 2015 Sep;70(9):822-9. doi: 10.1136/thoraxjnl-2015-206938. Epub 2015 Jun 5.


Background: There is limited data on the risk factors and phenotypical characteristics associated with spirometrically confirmed COPD in never-smokers in the general population.

Aims: To compare the characteristics associated with COPD by gender and by severity of airway obstruction in never-smokers and in ever-smokers.

Method: We analysed the data from 5176 adults aged 40 years and older who participated in the initial cross-sectional phase of the population-based, prospective, multisite Canadian Cohort of Obstructive Lung Disease study. Never-smokers were defined as those with a lifetime exposure of <1/20 pack year. Logistic regressions were constructed to evaluate associations for 'mild' and 'moderate-severe' COPD defined by FEV1/FVC <5th centile (lower limits of normal). Analyses were performed using SAS V.9.1 (SAS Institute, Cary, North Carolina, USA).

Results: The prevalence of COPD (FEV1/FVC<lower limits of normal) in never-smokers was 6.4%, constituting 27% of all COPD subjects. The common independent predictors of COPD in never-smokers and ever-smokers were older age, self reported asthma and lower education. In never-smokers a history of hospitalisation in childhood for respiratory illness was discriminative, while exposure to passive smoke and biomass fuel for heating were discriminative for women. COPD in never-smokers and ever-smokers was characterised by increased respiratory symptoms, 'respiratory exacerbation' events and increased residual volume/total lung capacity, but only smokers had reduced DLCO/Va and emphysema on chest CT scans.

Conclusions: The study confirmed the substantial burden of COPD among never-smokers, defined the common and gender-specific risk factors for COPD in never-smokers and provided early insight into potential phenotypical differences in COPD between lifelong never-smokers and ever-smokers.

Trial registration number: NCT00920348 (; study ID number: IRO-93326.

Keywords: COPD epidemiology; Clinical Epidemiology.

Publication types

  • Multicenter Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Airway Obstruction / physiopathology*
  • Canada
  • Cross-Sectional Studies
  • Female
  • Hospitalization
  • Humans
  • Logistic Models
  • Lung / physiopathology*
  • Male
  • Middle Aged
  • Prevalence
  • Prospective Studies
  • Pulmonary Disease, Chronic Obstructive / physiopathology*
  • Risk Factors
  • Smoking / adverse effects*
  • Tobacco Smoke Pollution / adverse effects*


  • Tobacco Smoke Pollution

Associated data