The effect of smoking on lung function: a clinical study of adult-onset asthma

The aim of this study was to evaluate the effect of smoking on lung function decline in adult-onset asthma in a clinical, 12-year follow-up study. In the Seinajoki Adult Asthma Study, 203 patients were followed for 12 years (1999-2013) after diagnosis of new-onset adult asthma. Patients were divided into two groups based on smoking history: <10 or >= 10 pack-years. Spirometry evaluation points were: 1) baseline, 2) the maximum lung function during the first 2.5 years after diagnosis (Max0-2.5) and 3) after 12 years of follow-up. Between Max0-2.5 and follow-up, the median annual decline in absolute forced expiratory volume in 1 s (FEV1) was 36 mL in the group of patients with <10 pack-years of smoking and 54 mL in those with smoking history >= 10 pack-years (p=0.003). The annual declines in FEV1 % pred (p=0.006), forced vital capacity (FVC) (p=0.035) and FEV1/FVC (p=0.045) were also accelerated in the group of patients with >= 10. pack-years smoked. In multivariate regression analysis, smoking history ?;10 pack -years became a significant predictor of accelerated decline in FEV1. Among patients with clinically defined adult-onset asthma, smoking history >= 10 pack-years is associated with accelerated loss of lung function.