COPD in Japan: The Nippon COPD Epidemiology study

Objectives: Despite high smoking rates, few prevalence studies of COPD have been performed in Asia. The Nippon COPD Epidemiology (NICE) Study used spirometry to measure prevalence of air-flow limitation in Japanese adults. Methodology: Clinical, spirometric, and risk factor exposure data were collected on 2343 subjects aged ≥ 40 years who were demographically similar to the Japanese population. Airflow limitation was defined according to Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria (FEV ₁/FVC < 70%). Results: Prevalence of airflow limitation was 10.9%. Based upon GOLD severity criteria, 56% of these cases were found to be mild, 38% moderate, 5% severe, and 1% very severe. Airflow limitation was significantly more prevalent in males than females (16.4% vs. 5.0%; P < 0.001), in male ever-smokers than female ever-smokers (17.1% vs. 7.5%; P < 0.001), and in older subjects (3.5% in 40-49 years olds vs. 24.4% in those > 70 years; P < 0.001). Of note, airflow limitation was also found in 5.8% of non-smokers and 4.6% of those younger than age 60 years. Only 9.4% of cases with airflow limitation reported a previous diagnosis of COPD. Conclusions: Prevalence of airflow limitation in Japan is higher than previously reported, suggesting a high degree of under-recognition of COPD. The high prevalence of smoking coupled with an aging population threatens to further increase the burden of COPD, highlighting the need for enhanced screening efforts and interventions of prevention and treatment.