In this issue of Thorax Lokke et al report the incidence of COPD in the Copenhagen City Heart Study.¹ They were able to do so because they followed a large cohort of representative citizens of Copenhagen for 25 years with spirometric tests, far longer than any previous such study. Non-asthmatics aged 30–60 years with normal initial spirometric parameters and good smoking histories were studied. About 2500 of them underwent spirometric tests at least twice (25 years apart), and vital status was ascertained in another 5500 who did not undergo comparable spirometric measurements. COPD was assessed in terms of the current standards for spirometry² staged according to GOLD.

More than 24% of the continuous smokers who underwent spirometric tests had COPD (defined as FEV₁<80% of predicted, FEV₁/FVC <70%) after 25 years, in stark contrast to never smokers in whom COPD occurred in <5%. Those who stopped smoking before or during the study did …