• copd epidemiology
• exercise

Physical activity is nowadays a widely accepted determinant of the progression of COPD.1 However, its role in preventing COPD development remains unclear. Several epidemiological analyses using population-based adult cohorts have reported longitudinal associations between higher physical activity levels and higher lung function levels, attenuated lung function decline and/or lower COPD incidence.2–7 In cohorts of patients with asthma8 9 or COPD,10 higher physical activity levels appear to attenuate lung function decline. In childhood, higher physical activity levels (assessed by accelerometer) relate to higher lung function at adolescence,11 which will likely impact on adult COPD risk.12

In the current issue of Thorax, Hansen et al 13 provide additional evidence supporting a role for physical activity on COPD risk, although they used physical fitness as a marker of physical activity. The authors report a longitudinal association between cardiorespiratory fitness (determined as maximal oxygen uptake (V̇O₂max) by ergometer test) and both COPD incidence and mortality in 4730 Danish adult men (mostly active smokers at baseline) followed for 46 years, after adjustment for age, socioeconomic status, smoking intensity, alcohol consumption, self-reported physical activity, body mass index, arterial hypertension and diabetes mellitus. In order to remove reverse causation (ie, COPD affects physical fitness via reduced physical activity), Hansen and colleagues restricted the analysis to events that happened 10 years or more after baseline. This approach is of special relevance because reverse …