AIR pollution may worsen cough and sputum when people with COPD walk for longer periods each day.
Air Pollution and Walking in COPD
Daily walking was associated with greater respiratory symptoms among people with chronic obstructive pulmonary disease (COPD), but the relationship depended partly on exposure to black carbon, a pollutant strongly associated with road traffic.
The multicenter panel study included 105 people with COPD from Catalonia, Spain, who were assessed during up to two separate seven-day periods. Participants had a mean age of 68 years, 20% were female, and mean forced expiratory volume in 1 second was 53% of the predicted value.
Activity monitors measured daily walking duration and step count. Researchers combined geolocation data with land-use regression models to estimate daily exposure to fine particulate matter measuring less than 2.5 µm, black carbon, and nitrogen dioxide. Participants recorded dyspnea, cough, sputum production, and wheezing each evening on a scale from 0–10.
Black Carbon Linked to Cough and Sputum
Longer walking duration was individually associated with higher cough and sputum levels. All three pollutants were associated with greater cough, while black carbon was also associated with increased sputum, dyspnea, and wheezing.
However, the interaction analysis revealed that longer daily walking was associated with greater cough and sputum only on days when black carbon concentrations were high. The interaction incidence rate ratio was 1.8 for cough and 2.0 for sputum.
No significant interaction was identified between walking duration and either fine particulate matter or nitrogen dioxide. Analyses using step count produced similar findings.
The interaction pattern remained after excluding people who currently smoked, although it was no longer statistically significant. Other sensitivity analyses, including the exclusion of participants with asthma and extreme exposure values, produced broadly consistent results.
Walking Should Still Be Encouraged
The findings do not suggest that walking should be discouraged in people with COPD. Regular physical activity remains important for COPD prognosis, and walking may acutely promote airway clearance by increasing ventilation and helping expel existing secretions.
Instead, the results support recommending low-traffic walking routes when possible. Black carbon particles may penetrate deeply into the lungs and contribute to oxidative stress, mucus production, epithelial injury, and airway inflammation.
The short monitoring period, limited number of female participants, estimated rather than directly measured outdoor pollution exposure, and lack of daily rescue medication data should be considered when interpreting the results.
Accessible, low-traffic spaces may help people with COPD gain the long-term benefits of walking while reducing exposure to traffic-related air pollution.
Reference
Josa-Culleré A et al. Effects of the interaction between walking activity and air pollution on daily respiratory symptoms in people with COPD. Thorax. 2026;doi:10.1136/thorax-2025-224411.
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