Background: The frequency of smokers among asthma patients often mirrors the frequency of smokers among healthy individuals. Smoking has been shown to increase the lung function decline in adult asthma patients and change the composition of the bronchial inflammation.
Objective: To examine the consequences of smoking in a large cohort of young asthma patients.
Methods: Seven hundred ninety-three asthma patients, aged 14 to 44, were examined using lung function measurements, bronchial provocations, clinical interviews, and questionnaires.
Results: Forty-five percent of participants were smokers; smokers had significantly lower forced expiratory volume in one second (FEV(1)), FEV(1) in percent of predicted value (FEV(1)% pred), and FEV(1)/forced vital capacity (FVC) values compared with nonsmokers, and there was a dose-response relationship between tobacco exposure and these lung function measures. Smoking seemingly affected the FEV(1) growth already in adolescence, and before the age of 45, significantly more smokers than nonsmokers had signs of airflow limitation, with FEV(1)/FVC ratios below 0.70. Smokers had more asthma symptoms despite receiving inhaled corticosteroid (ICS) treatment as frequently as did nonsmokers.
Conclusion: The additive effect of smoking on lung function decline in asthma patients is detectable at early ages and leads to signs of airflow limitation before the age of 45 years.