Independent and joint relationships of cardiorespiratory fitness and body mass index with liver fat content.

Aims: To investigate the relationship between cardiorespiratory fitness (CRF) and liver fat content (LFC) in community-based participants and highlight their relationship in people with different body mass indices (BMIs).

Materials And Methods: Using UK Biobank data, CRF was estimated with bicycle ergometer fitness testing and was evaluated based on physical work capacity at 75% maximum heart rate (PWC). LFC was quantified through liver proton density fat fraction (PDFF) on magnetic resonance imaging. Multivariate linear regression models were used to analyse the associations of CRF and BMI with absolute reduction and percentage change in PDFF (%).

Results: In total, 5765 participants with a mean age of 55.57 years and a median (range) follow-up of 10.7 (4.0-17.7) years were included. Compared with the lowest PWC tertile, the absolute reduction and percentage change in PDFF in the highest PWC tertile were -0.450 (95% confidence interval [CI] -0.699 to -0.192) and -4.152 (95% CI -6.044 to -2.104), respectively. These associations were independent of BMI, and individuals with obesity and normal weight had the largest absolute reduction and percentage change in LFC, respectively (p for interaction <0.001). Joint analysis showed that PWC and BMI had a negative dose-response relationship with PDFF. These associations were consistent in different sex and age subgroups (p for interaction >0.05).

Conclusions: There was a significant negative association between CRF and LFC, and this association was independent of BMI. The results of this study strongly recommend improving CRF to mitigate LFC.