Obesity and the risk of idiopathic pulmonary fibrosis: a nationwide population-based study

Background Obesity is a chronic inflammatory and metabolic condition implicated in the pathogenesis of several fibrotic diseases. However, population-based evidence regarding the association between obesity and the risk of idiopathic pulmonary fibrosis (IPF) remains limited.Methods This is a nationwide population-based cohort study using the National Health Information Database of South Korea. Adults aged ≥20 years who participated in the National Health Screening Program in 2012 were included. Individuals with prevalent IPF or those diagnosed within 1 year after baseline were excluded. Obesity was assessed using body mass index (BMI ≥25 kg/m² by Asian criteria) and waist circumference (WC). Incident IPF was defined by insurance claims with the International Classification of Diseases, 10th Revision code J84.1 in conjunction with registration in the Rare Intractable Diseases programme.Results Among 4 788 202 participants followed for a mean of 10.15 years, 1 591 830 (33.2%) were classified as obese. Higher BMI was associated with an increased risk of IPF in a dose–response manner after multivariable adjustment. Compared with participants with BMI 18.5–22.9 kg/m², adjusted HRs for IPF were 1.25 (95% CI 1.16 to 1.35) for BMI 23–24.9 kg/m², 1.55 (95% CI 1.45 to 1.66) for BMI 25–29.9 kg/m² and 1.66 (95% CI 1.42 to 1.94) for BMI ≥30 kg/m². In contrast, underweight individuals (BMI <18.5 kg/m²) had a lower risk of IPF. WC demonstrated a similar trend, with higher values independently associated with increased IPF risk.Conclusions In this large nationwide cohort, both general and abdominal obesity were independently associated with an increased risk of incident IPF. These findings provide population-based evidence supporting a potential role of increased adiposity in IPF pathogenesis.