Association between air pollution and physical activity in patients with COPD

Knowledge on the environmental determinants of physical activity in COPD is scarce and no information on the specific role of air pollution is available. We aimed to explore the association between air pollution and physical activity in COPD patients, hypothesizing that higher levels of air pollution may negatively impact on physical activity. This is a cross-sectional analysis of baseline pre-randomisation data from the multi-centre Urban Training study (NCT01897298) in Catalonia. We estimated annual residential averages of nitrogen dioxide (NO2) and particulate matter (PM2.5, PM10 and PM2.5absorbance) using land-use regression models. We assessed physical activity (daily step count and sedentary time) using the Dynaport MoveMonitor, and physical activity experience using the C-PPAC difficulty score. We built mixed-effect linear regression models for each outcome and exposure, adjusting for confounders with a random intercept for the city area. We included 407 patients (mean (SD) 69 (8) y, 85% male, FEV1 57% pred); median (p25-p75) levels of air pollutants were at the WHO health limits (NO2 43.5 µg/m3 [35.0-48.7]; PM2.5 12.6 µg/m3 [10.7-13.8]; PM10 24.9 µg/m3 [22.3-27.7]). Multi-variable analysis showed an association between NO2 and sedentary time (Coef=0.23 [95% CI 0.03, 0.43] per IQR change, p=0.027) and C-PPAC difficulty (-2.57 [-5.12, -0.02] per IQR change, p=0.048). No other significant associations were observed. In COPD patients, higher NO2 levels of residential areas are associated with increased sedentary times and the experience of increased difficulty during physical activity. This likely contributes to the negative effects of air pollution in COPD patients and requires further investigation.