Association of asthma and smoking with lung function impairment in adolescence and early adulthood: the Isle of Wight Birth Cohort Study

We investigated associations of asthma and smoking with lung function and airway reversibility from childhood to early adulthood.The population-based Isle of Wight Birth Cohort (n=1456) was assessed at birth, and at 1, 2, 4, 10, 18 and 26 years. Asthma was defined as physician diagnosis plus current wheeze and/or treatment. Spirometry was conducted at 10 (n=981), 18 (n=839) and 26 years (n=547). Individuals were subdivided into nonsmokers without asthma, nonsmokers with asthma, smokers without asthma and smokers with asthma, based on asthma and smoking status at 26 years. Their lung function trajectories from 10 to 26 years were examined using longitudinal models.Nonsmokers with asthma had smaller forced expiratory volume in 1 s (FEV ), FEF (forced expiratory flow at 25-75% of forced vital capacity (FVC)) and FEV /FVC ratio compared to nonsmokers without asthma at age 10 and 18 years, with differences reduced after bronchodilator (pre-bronchodilator FEV at 26 years 3.75 L 4.02 L, p