The association of impaired lung function and nonalcoholic fatty liver disease: a systematic review

Background and aims Nonalcoholic fatty liver disease (NAFLD) and impaired lung function share similar risk factors and phenotypes, such as obesity and type 2 diabetes. The study is an updated meta-analysis to evaluate the association between NAFLD and impaired lung function. Methods A total of 696 articles were identified with mention of NAFLD and lung function (or pulmonary function testing) in MEDLINE, EMBASE, and Scopus. After de-duplication, 455 articles were screened, 18 underwent full-text review. Five studies met our review and inclusion criteria with an interrater reliability kappa score of 1. Results Five studies with a total of 118 118 subjects (28.4% with NAFLD) were included. The cross-sectional studies supported a statistically significant relationship between decreased pulmonary function tests and NAFLD. There was no association observed with obstructive lung pattern. One of the longitudinal studies revealed an association with increased rate of decline in forced vital capacity in patients with NAFLD and FIB4 score ≥1.30 (-21.7 vs. -27.4 mL/year, P = 0.001 in males, -22.4 vs. -27.9 mL/year, P = 0.016 in females). The second longitudinal study revealed that patients with impaired pulmonary function had an increased hazard ratio of developing NAFLD dependent on the severity of pulmonary impairment. Conclusions This is the first systematic review that supports an association of NAFLD with decreased (restrictive) lung function. The estimated severity of liver fibrosis correlates with the rate of progression of restrictive lung function. There are also data showing that patients with impaired lung function have a higher risk of developing NAFLD.