Smoking cessation and lung function in mild-to-moderate chronic obstructive pulmonary disease - The Lung Health Study

Previous studies of lung function in relation to smoking cessation have not adequately quantified the long-term benefit of smoking cessation, nor esta blished the predictive value of characteristics such as airway hyperrespons iveness. In a prospective randomized clinical trial at 10 North American me dical centers, we studied 3,926 smokers with mild-to-moderate airway obstru ction (3,818 with analyzable results; mean age at entry, 48.5 yr; 36% women ) randomized to one of two smoking cessation groups or to a nonintervention group. We measured lung function annually for 5 yr. Participants who stopp ed smoking experienced an improvement in FEV1 in the year after quitting (a n average of 47 ml or 2%). The subsequent rate of decline in FEV1 among sus tained quitters was half the rate among continuing smokers, 31 +/- 48 versu s 62 +/- 55 ml (mean +/- SD), comparable to that of never-smokers. Predicto rs of change in lung function included responsiveness to beta-agonist, base line FEV1, methacholine reactivity, age, sex, race, and baseline smoking ra te. Respiratory symptoms were not predictive of changes in lung function. S mokers with airflow obstruction benefit from quitting despite previous heav y smoking, advanced age, poor baseline lung function, or airway hyperrespon siveness.