Smoking cessation and changes in respiratory symptoms in two populations followed for 13 years.

To investigate the relationship between persistence and incidence rates of respiratory symptoms, and the cessation of cigarette smoking, the data from longitudinal studies conducted in Cracow, Poland and Tucson, USA were analysed jointly. Among 1722 subjects smoking at the beginning of the study, 468 had given up smoking at the 13-year follow-up. The persistence and incidence rates of chronic cough, chronic phlegm, wheeze and attacks of breathlessness were reduced by 50% in ex-smokers compared to the subjects continuing to smoke. The beneficial effects of smoking cessation were decreased in subjects smoking more cigarettes per day in the past and starting to smoke at a younger age. The symptoms were less likely if smoking ceased before the onset of any respiratory disease. These results were similar in the Cracow and Tucson populations, confirming the universal nature of the observations.