Even after excluding subjects aged 18 to 24 years, the prevalence continues to be low in the Korean sample (10.5%). In a comparison of the prevalence for each age-sex group by ATS criteria to the same criteria in the Po Delta, the Korean rates remain substantially lower.
The prevalence of airway obstruction in Ansan City was also lower than those in the United States, based on data from the Third National Health and Nutrition Examination Survey III from 1988 to 1994. In the latter report, the proportion of the population with low lung function (defined as an FEV1/FVC ratio of < 70% and FEV1 of <80% predicted) was 6.8% among those aged а 17 years. In contrast, only 1.4% of Ansan City residents had low lung function based on the same criteria. Link
Geographic variation in the prevalence of COPD was found in the Epidemiological Study of Chronic Obstructive Pulmonary Disease in Spain (IBERPOC), which was conducted in seven different areas of Spain. Ansan City might be comparable to the area in the IBERPOC study with the lowest prevalence of the disease (4.9% by European Respiratory Society criteria), even though the subjects in the IBERPOC study (age range, 40 to 69 years) were older than those in the Ansan City sample. Here, in the IBERPOC study, asthma was excluded, and FVC was used instead of VC for defining COPD. This could partly explain the low prevalence in the region investigated in the IBERPOC study.
The results from the above comparison only suggest that airway obstruction is less prevalent in Korea than in the West, but more definitive comparisons need to be made based on standardized research protocols. The relatively low rate of patients with obstructive airway disease in Japan compared with those in Western countries, further suggests that low rates of airway obstruction are characteristic of Asia in general.