Abstract
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 [FEV(1)] and forced vital capacity [FVC]), prior-day personal pollutant exposure measured by portable air quality monitors (fine particulate matter [PM(2.5)] nitrogen oxide [NO(2)], and ozone [O(3)]), 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 O(3) but not NO(2). Each interquartile range (IQR) increment in step count was associated with 0.97 µg/m(3) (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 O(3) in adjusted models. We observed an interaction between prior-day NO(2) and step count on FEV(1) and FVC (P(interaction)<0.05) in which the negative associations between NO(2) and lung function were reduced or absent at higher levels of daily activity. For example, FEV(1) was 28.5mL (95%CI: -41.0, -15.9) lower per IQR of NO(2) 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 O(3) and may attenuate the association between NO(2) exposure and lung function.