Epidemiology of interstitial lung diseases in Japan: A nationwide database analysis

Interstitial lung disease (ILD) comprises a wide range of pulmonary disorders associated with high morbidity and mortality. Although idiopathic pulmonary fibrosis (IPF) has been the focus of much prior research, population-level data covering the full spectrum of ILD in Japan remain limited.

This retrospective cohort study used the National Database of Health Insurance Claims (NDB) in Japan to identify patients diagnosed with ILD from January 2015 to December 2023. We analyzed annual prevalence, incidence, patient demographics, and survival outcomes overall and by ILD subtypes.

A total of 2,758,542 patients with ILD were identified during the study period. ILD prevalence nearly doubled, from 656 per 100,000 population in 2015 to 1301 per 100,000 in 2023, while incidence remained relatively stable (192 per 100,000 in 2015 to 212 per 100,000 in 2023), with a notable decline observed in 2020 (178 per 100,000). Males consistently had higher prevalence and incidence than females. Age and sex distributions differed substantially across ILD subtypes. The overall 5-year survival rate was 59.9 %, with IPF demonstrating the poorest survival (32.1 %).

This nationwide study provides the most comprehensive epidemiological overview of ILD in Japan to date. The insights gained can support evidence-based healthcare planning and help guide priorities for future research and clinical improvements.