BACKGROUND & AIMS The association between nonalcoholic fatty liver disease (NAFLD) and pulmonary function remains elusive because of the heterogeneous spectrum and inaccurate diagnostic methods of NAFLD, and insufficient pulmonary function data. We conducted this study to identify the association between histological severity of NAFLD and pulmonary function.

METHODS This study included patients ≥18 years old with baseline pulmonary function data between August 2014 and July 2019 within a biopsy-evaluated prospective NAFLD cohort. Cross-sectionally, pre-/post-bronchodilator spirometric data with diffusing capacity (DL_CO ) were compared according to histological severity of NAFLD in the various demographic and metabolic subgroups. Multivariable-adjusted analysis revealed specific histological features associated with reduced pulmonary function.

RESULTS In a total of 420 patients with biopsy-proven NAFLD, pre-/post-bronchodilator forced vital capacities (FVCs; a percentage of the predictive value) were inversely correlated with histological severity of NAFLD. Conversely, pre-bronchodilator forced expiratory volume in 1 second (FEV₁ )/FVC was positively correlated with NAFLD severity. Post-bronchodilator FVC (%) decreased and DL_CO /alveolar volume (V_A ) increased linearly with worsening histological severity of NAFLD in multivariable analysis. In particular, fibrosis stage remained a significant independent predictor of decreased post-bronchodilator FVC (%) (β-coefficient, 4.41; 95% confidence interval [-8.39, -0.43]; P = .031) even after adjusted for clinical variables, exclusively in age <65 years, female, never-smoker and nonchronic obstructive pulmonary disease subgroups.

CONCLUSIONS Pulmonary function deteriorates with worsening histological severity of NAFLD, especially at the fibrosis stage. The common pathogenesis of reduced pulmonary function and NAFLD fibrosis progression should be further explored.