Physical Activity, Air Pollution Exposure, and Lung Function Interactions Among Adults with COPD.

Rationale: Although physical activity is strongly encouraged for patients with chronic obstructive pulmonary disease (COPD), it is unknown if physical activity affects daily exposure to air pollution, or whether it attenuates or exacerbates the effects of pollution on the airways among adults with COPD.

Methods: Thirty former smokers with moderate-to-severe COPD in Boston were followed for 4 non-consecutive months in different seasons. We assessed daily lung function (forced expiratory volume in 1 second [FEV₁] and forced vital capacity [FVC]), prior-day personal pollutant exposure measured by portable air quality monitors (fine particulate matter [PM_2.5] nitrogen oxide [NO₂], and ozone [O₃]), and daily step count. We constructed multi-level linear mixed-effects models with random intercepts for person and person-observation month, adjusting for demographic/seasonal covariates to test if step count was associated with daily pollution exposure, and if associations between prior-day pollution and lung function differed based on prior-day step count. Where effect modification was found, we performed stratified analyses by tertile of step count.

Results: Higher daily step count was associated with higher same-day personal exposure to PM_2.5, and O₃ but not NO₂. Each interquartile range (IQR) increment in step count was associated with 0.97 µg/m³ (95%CI: 0.30, 1.64) higher exposure to PM_2.5 and 0.15 parts per billion (95% CI: -0.05, 0.35) higher exposure to O₃ in adjusted models. We observed an interaction between prior-day NO₂ and step count on FEV₁ and FVC (P_interaction<0.05) in which the negative associations between NO₂ and lung function were reduced or absent at higher levels of daily activity. For example, FEV₁ was 28.5mL (95%CI: -41.0, -15.9) lower per IQR of NO₂ in the lowest tertile of step count, but there was no association in the highest tertile of step count (-1.6mL, 95% CI: -18.4, 15.2).

Conclusions: Higher physical activity was associated with modestly higher daily exposure to PM_2.5 and O₃ and may attenuate the association between NO₂ exposure and lung function.