Lung Function and Respiratory Symptoms as Factors Associated with Smoking Cessation Status in a Population-Based Study

Background/Objectives: The aim of this study was to test the association of poorer spirometry and more respiratory symptoms with being an ex-smoker in a cohort of ever-smokers in a population-based study in Kazakhstan. Methods: We first enrolled 5058 subjects, of whom 1769 were classified as ever-smokers (63% current and 37% former smokers) from the general population in five cities in Kazakhstan and analyzed them hereinafter. They filled in a questionnaire and underwent spirometry with bronchodilation, in which z-scores of post-bronchodilation forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were analyzed. Respiratory symptoms and spirometry were compared between continuing smokers and those who stopped in multivariate logistic regression models. Results: Current smokers smoked a median of 10 (interquartile range (IQR) 7;20) cigarettes a day. In the fully adjusted models, neither lung function (FEV1, FVC and FEV1/FVC z-scores and even FEV1/FVC below the lower limit of normality (LLN)) nor symptoms could predict being an ex-smoker at present. Age (odds ratio (OR) 1.02; 95% confidence interval (CI) 1.01; 1.03), body mass index (BMI) over 25 kg/m2 (OR 1.36; 95% CI 1.10; 1.68), lifetime exposure to vapor, gas, dust and fume (OR 0.77; 95% CI 0.62; 0.97), exposure to SHS (OR 0.34; 95% CI 0.27; 0.42) and electronic cigarette use (OR 0.58; 95% CI 0.34;0.99) were significantly associated with being a former smoker vs. a current smoker at the time of examination. Conclusions: Spirometry and early respiratory symptoms did not predict being a former smoker, but co-exposure to secondhand smoke, occupational exposures, and electronic cigarette use sustain continuing smoking.