Supplementary Material for: The Effect of Hidden Female Smoking on the Association between Smoking and Asthma

Background: The association between smoking and asthma remains controversial. In our previous study, we were not able to show an association between asthma and smoking in Korean adults. One Korean study demonstrated underreporting of smoking history by female adults. The aim of the present study was to investigate the effects of hidden female smoking on the association between asthma and smoking in Korean adults. Methods: Data were acquired from 23,483 men and women aged ≥19 years who participated in the Korean National Health and Nutrition Examination Surveys (KNHANES). Results: The prevalence of asthma was 1.5%, the self-reported smoking prevalence was 32.4%, and the cotinine-verified smoking prevalence was 30.3%. Of the male cotinine-verified smokers, 6.4% were self-reported nonsmokers (2.7% never smokers and 3.7% ex–smokers), whereas 48.8% of the female cotinine-verified smokers were self-reported nonsmokers (43.2% never smokers and 5.6% ex–smokers). In males, the adjusted odds ratio of the association between smoking and asthma was 0.738 (confidence interval, CI: 0.393–1.173) in self-reported and 0.767 (CI: 0.515–1.143) in cotinine-verified smoking; in females, the adjusted odds ratio was 1.945 (CI: 1.348–2.805) in self-reported and 1.531 (CI: 1.076–2.179) in cotinine-verified smoking. Conclusions: Our study showed smoking was associated with asthma in females but not in males.