Dose-related effect of urinary cotinine levels on pulmonary function among Korean women

SETTING: Country-wide general population in South Korea. BACKGROUND: The dose-response relationship between smoking and pulmonary function in women may have been significantly over-estimated by studies that employed a self-reporting questionnaire. OBJECTIVE: To evaluate whether this relationship was still observed among Korean women when smoking levels were determined by urinary cotinine measurements. DESIGN: A total of 4584 Korean women from the spirometry data set of the Korean National Health and Nutrition Examination Surveys IV and V (2008-2010) were included. Analysis of covariance was performed to estimate the dose-related effect of urinary cotinine levels on pulmonary function after adjusting for covariates in this country-wide cross-sectional study. RESULTS: Compared to urinary cotinine levels (cut-off 50 ng/ml), the false-positive rate of self-reported smoking was 53.2%. After the smokers were divided into deciles, the regression coefficients for percentage forced expiratory volume in 1 second (FEV₁%) and percentage forced expiratory volume/forced volume capacity (FEV₁/ FVC) ratio (FEV₁/FVC%) were -0.2903 and -0.2680 (%/decile), respectively (both P < 0.001). CONCLUSION: It is necessary to use objective methods when determining the smoking status of Korean women. Even after reducing information bias, smoking affected pulmonary function in a dose-dependent manner.