Dose-dependent association of smoking and bronchial hyperresponsiveness.

Our aim was to study the association of smoking habits and environmental tobacco smoke (ETS) exposure with bronchial hyperresponsiveness (BHR). A random sample of 292 adults was examined using a structured interview, spirometry, skin prick tests, exhaled nitric oxide fraction (FeNO) and bronchial histamine challenge. A large majority of subjects with BHR were smokers or ex-smokers. Starting to smoke before 20 years of age was significantly associated with BHR, as was current smoking, quantity of smoking and ETS exposure. The severity of BHR increased significantly with increasing pack-years of exposure (p<0.001). Current smokers with decreased lung function were at a particularly high risk of BHR. Impaired forced expiratory volume in 1 s and mean maximal expiratory flow were independent determinants for more severe BHR, regardless of age. In multivariate analysis, smoking remained an independent determinant for BHR after adjustment for impaired lung function and other covariates: ≥15 pack-years yielded an odds ratio of 3.00 (95% CI 1.33-6.76) for BHR. The association between BHR and FeNO was dependent on smoking habits. The results indicate that smoking is a significant risk factor for BHR, with a dose-dependent pattern, and that the severity of BHR increases with pack-years. The findings strongly suggest assessment of smoking habits in subjects with BHR.