Factors independently associated with cardiorespiratory fitness in patients with non-alcoholic fatty liver disease.

ABSTRACT

Low cardiorespiratory fitness (CRF) is associated with non-alcoholic fatty liver disease (NAFLD) and low CRF is an important risk factor for cardiovascular disease. The factors that influence CRF in NAFLD are poorly understood and it has been suggested that reduced hepatic mitochondrial function (HMF) may be linked to low CRF. Therefore, our aim was to determine the factors associated with CRF in NAFLD. METHODS: Ninety-seven patients with NAFLD were studied. CRF was assessed by treadmill testing and expressed as maximal O2 consumption (VO2 peak) per lean body mass. HMF was assessed by the 13 C-ketoisocaproate breath test. Multivariable linear regression modelling was undertaken to test the independence of associations with CRF. RESULTS: Mean (SD) age was 51 (13) years and 61% were men. With CRF as the outcome, age (B coefficient -0.3, 95%CI -0.4, -0.2, P < .0001), total body fat mass (B coefficient -0.2, 95%CI -0.3, -0.05, P = .01), type 2 diabetes mellitus (T2DM) (B coefficient -3.6, 95%CI -1.1, -6.1, P = .005), smoking status (B coefficient -5.7, 95%CI -1.9, -9.5, P = .004), serum γ-glutamyl transferase (GGT) (B coefficient -0.04, 95%CI -0.05, -0.02, P < .0001), HMF (B coefficient -0.5, 95%CI -0.8, -0.1, P = .01) and diastolic function (B coefficient 0.1, 95%CI 0.05, 0.13, P < .0001) were independently associated with CRF. This model explained 60% of the total variance in CRF (R2  = 0.6, P < .0001); and this model with GGT alone explained 24% of the variance in CRF. CONCLUSIONS: In patients with NAFLD, HMF is independently associated with CRF and a model with GGT alone explained most of the variance in CRF.