Association between non-alcoholic fatty liver disease and decreased lung function in adults: a systematic review and meta-analysis

AIM: Recent observational studies assessed the association between non-alcoholic fatty liver disease (NAFLD) and lung function in adults, but the magnitude of this association remains uncertain. We estimated the magnitude of the association between NAFLD and lung function on spirometry (predicted forced expiratory volume in 1 sec [FEV1] and forced vital capacity [FVC]). METHODS: - We searched publication databases using predefined keywords to identify studies (published up to October 4, 2018), in which NAFLD was diagnosed by imaging or biochemistry (no studies with biopsy-proven NAFLD were available). Data from selected studies were extracted, and meta-analysis was performed using random-effects modelling. RESULTS: - Six observational studies (5 cross-sectional and 1 longitudinal) with aggregate data on 133,707 individuals (27.8% with NAFLD) of predominantly Asian ethnicity (74.6%) were included in the final analysis. There were significant differences in predicted FEV1 (n = 5 studies; pooled weighted mean difference [WMD]: -2.43%, 95%CI -3.28 to -1.58; I2 = 69.7%) and predicted FVC (pooled WMD: -2.96%, 95%CI -4.75 to -1.17; I2 = 91.7%) between individuals with and without NAFLD. Decreased FEV1 and FVC at baseline were also independently associated with a ~15% increased risk of incident NAFLD (n = 1 study in Korean individuals). Subgroup analyses did not materially modify these findings. CONCLUSIONS: - NAFLD is associated with significant reductions of both FEV1 and FVC in Asian and United States adults, and such small, but significant, reductions of lung volumes at baseline may be also associated with increased NAFLD incidence in Asian individuals. Further research is needed to better elucidate the link between NAFLD and impaired lung volumes.