Effects of the interaction between walking activity and air pollution on daily respiratory symptoms in people with COPD

Objectives: Walking activity can improve the prognosis of people with chronic obstructive pulmonary disease (COPD), but might worsen the harmful effects of pollution if practised in polluted environments. We aimed to determine the combined effect of walking activity and air pollution on daily respiratory symptoms in people with COPD. Methods: This multicentre panel study assessed 105 people with COPD from Catalonia (Spain) over two 7 days periods. Daily walking activity (walking duration, step count) was measured via activity monitors. Daily air pollutant concentration (particulate matter with an aerodynamic diameter <2.5 µm (PM_2.5), black carbon (BC), nitrogen dioxide (NO₂)) was estimated by combining geolocation data with land use regression models. Dyspnoea, cough, expectoration and wheezing were recorded in diaries every evening (0–10 scale). We estimated the individual association of daily walking activity and air pollution and their interaction on symptoms using multivariable mixed-effects negative binomial models. Results: Participants (20% female) were mean±SD 68±7 years old and had a forced expiratory volume in 1 s of 53±23% predicted. Walking duration was associated with higher levels of cough and expectoration. All pollutants were associated with higher cough and BC also with higher expectoration, dyspnoea and wheezing. After including an interaction term, more walking duration was associated with higher cough and expectoration only on days with high BC concentrations (p for interaction <0.05). No interaction was observed between walking duration and PM_2.5 or NO₂. Results were similar for step count. Conclusions: Daily walking activity may worsen cough and expectoration in people with COPD when BC concentrations are high. Actions to ensure accessible low-traffic spaces to walk are paramount.