Overlap syndrome shares features of both asthma and chronic obstructive pulmonary disease (COPD). The aim of this study was to investigate characteristics of overlap syndrome and their effect on self-rated health (SRH).
We analyzed data from the Fourth Korea National Health and Nutrition Examination Survey of 2007–2009. Subjects with acceptable spirometry and available wheezing history were included. Subjects were classified into four groups based on forced expiratory volume in one second (FEV 1)/forced vital capacity (FVC) results and the presence or absence of self-reported wheezing for the previous 12 months: 1) COPD group, defined as having FEV 1/FVC <0.7 without self-reported wheezing history; 2) asthma group, defined as having self-reported wheezing history without FEV 1/FVC <0.7; 3) overlap syndrome group, having both FEV 1/FVC <0.7 and wheezing history; and 4) non-obstructive disease (NOD) group, having neither FEV 1/FVC <0.7 nor self-reported wheezing. SRH was categorized as better or lower based on responses to a questionnaire.
From a total 9,104 subjects, 700 were assigned to the COPD group, 560 to the asthma group, 210 to the overlap syndrome group, and 7,634 to the NOD group. Compared to the other groups, subjects in the overlap syndrome group were more likely to have low lung function, a high proportion of smokers, low socioeconomic status, short education duration, lower SRH, and past diagnosis of pulmonary tuberculosis or bronchiectasis. Multiple logistic regression analysis revealed that both overlap syndrome and asthma groups were independently associated with lower SRH after adjustment for age, sex, socioeconomic status, education level, smoking status, comorbidities, and lung function. Female, old age, low education level, low economic status, smoker and other comorbidities were also associated with lower SRH.