In recent years, a wealth of factors are associated with increased risk of developing non-alcoholic fatty liver disease (NAFLD) and NAFLD is now thought to increase the risk of multiple extra-hepatic diseases. The aim of this review is first to focus on the role of ageing and sex as key, poorly understood risk factors in the development and progression of NAFLD. Secondly, we aim to discuss the roles of white adipose tissue (WAT) and intestinal dysfunction, as producers of extra-hepatic factors known to further contribute to the pathogenesis of NAFLD. Finally, we aim to summarise the role of NAFLD as a multi-system disease affecting other organ systems beyond the liver. Both increased age and male sex increase the risk of NAFLD and this may be partly driven by alterations in the distribution and function of WAT. Similarly, changes in gut microbiota composition and intestinal function with ageing and chronic overnutrition are likely to contribute to the development of NAFLD both directly (i.e. by affecting hepatic function) and indirectly via exacerbating WAT dysfunction. Consequently, the presence of NAFLD significantly increases the risk of various extra-hepatic diseases including CVD, type 2 diabetes mellitus, chronic kidney disease and certain extra-hepatic cancers. Thus changes in WAT and intestinal function with ageing and chronic overnutrition contribute to the development of NAFLD – a multi-system disease that subsequently contributes to the development of other chronic cardiometabolic diseases.

Background: Type 2 diabetes mellitus (T2DM) is a strong risk factor for liver fibrosis in non-alcoholic fatty liver disease (NAFLD). It remains uncertain why T2DM increases the risk of liver fibrosis. It has been suggested that growth differentiation factor-15 (GDF-15) concentrations increase the risk of liver fibrosis. We aimed to investigate (a) whether GDF-15 concentrations were associated with liver fibrosis and involved in the relationship between T2DM and liver fibrosis and (b) what factors linked with T2DM are associated with increased GDF-15 concentrations. Methods: Ninety-nine patients with NAFLD (61% men, 42.4% T2DM) were studied. Serum GDF-15 concentrations were measured by electro-chemiluminescence immunoassay. Vibration-controlled transient elastography (VCTE)-validated thresholds were used to assess liver fibrosis. Regression modelling, receiver operator characteristic curve analysis and Sobel test statistics were used to test associations, risk predictors and the involvement of GDF-15 in the relationship between T2DM and liver fibrosis, respectively. Results: Patients with NAFLD and T2DM (n = 42) had higher serum GDF-15 concentrations [mean (SD): 1271.0 (902.1) vs. 640.3 (332.5) pg/ml, p < 0.0001], and a higher proportion had VCTE assessed ≥F2 fibrosis (48.8 vs. 23.2%, p = 0.01) than those without T2DM. GDF-15 was independently associated with liver fibrosis (p = 0.001), and GDF-15 was the most important single factor predicting ≥F2 or ≥F3 fibrosis (≥F2 fibrosis AUROC 0.75, (95% CI 0.63–0.86), p < 0.001, with sensitivity, specificity, positive predictive (PPV) and negative predictive (NPV) values of 56.3%, 86.9%, 69.2% and 79.1%, respectively). GDF-15 was involved in the association between T2DM and ≥F2 fibrosis (Sobel test statistic 2.90, p = 0.004). Other factors associated with T2DM explained 60% of the variance in GDF-15 concentrations (p < 0.0001). HbA1c concentrations alone explained 30% of the variance (p < 0.0001). Conclusions: GDF-15 concentrations are a predictor of liver fibrosis and potentially involved in the association between T2DM and liver fibrosis in NAFLD. HbA1c concentrations explain a large proportion of the variance in GDF-15 concentrations.

Background and Aims: The impact of metabolic syndrome (MetS) traits on chronic kidney disease (CKD) risk in metabolic dysfunction‐associated steatotic liver disease (MASLD) is unknown. We investigated the impact of type and number of MetS traits and liver fibrosis on prevalent CKD and incident end‐stage renal disease (ESRD) risk in SLD. Methods: 234 488 UK Biobank participants' were analysed. Hepatic steatosis index (> 36 for SLD, < 30 for no SLD) and MRI‐proton density fat fraction (≥ 5.56%) were used to identify SLD. MetS traits were identified using MASLD criteria. Advanced fibrosis (FIB‐4 score > 2.67) was determined using FIB‐4 scores. eGFR < 60 mL/min/1.73 m ² or albuminuria > 3 mg/mmol identified prevalent CKD. A validated algorithm identified incident ESRD. Binary logistic and Cox regressions were used to test associations with prevalent CKD ([adjusted odds ratios (ORs)]) and incident ESRD (adjusted hazard ratios [HRs]) respectively. Results: 102 410 participants (41.2%) had SLD. 64.4% had MetS. 1.3% had FIB‐4 score > 2.67. With SLD and only one MetS trait, hypertension (OR 1.35, 95% CI 1.35–1.72) or type 2 diabetes (T2D) (OR 1.89, 95% CI 1.06–3.38) increased risk of prevalent CKD. MetS (≥ 3 traits) increased prevalent CKD risk (OR 1.94, 95% CI 1.75–2.15), which was further increased by advanced liver fibrosis (OR 4.29, 95% CI 3.36–5.47). CKD prevalence increased with increasing MetS traits. Over 13.6 years (median follow‐up), MetS was associated with increased risk of developing ESRD (HR 1.70, 95% CI 1.19–2.43). Conclusions: In MASLD, hypertension, and T2D, number of MetS traits and liver fibrosis increased risk of prevalent CKD and presence of MetS increased the risk of incident ESRD.

Affecting approximately 25% of the global population, steatotic liver disease (SLD) poses a significant health concern. SLD ranges from simple steatosis to metabolic dysfunction-associated steatohepatitis and fibrosis with a risk of severe liver complications such as cirrhosis and hepatocellular carcinoma. SLD is associated with obesity, atherogenic dyslipidaemia, and insulin resistance, increasing cardiovascular risks. As such, identifying SLD is vital for cardiovascular disease (CVD) prevention and treatment. Bile acids (BAs) have critical roles in lipid digestion and are signalling molecules regulating glucose and lipid metabolism and influencing gut microbiota balance. BAs have been identified as critical mediators in cardiovascular health, influencing vascular tone, cholesterol homeostasis, and inflammatory responses. The cardio-protective or harmful effects of BAs depend on their concentration and composition in circulation. The effects of certain BAs occur through the activation of a group of receptors, which reduce atherosclerosis and modulate cardiac functions. Thus, manipulating BA receptors could offer new avenues for treating not only liver diseases but also CVDs linked to metabolic dysfunctions. In conclusion, this review discusses the intricate interplay between BAs, metabolic pathways, and hepatic and extrahepatic diseases. We also highlight the necessity for further research to improve our understanding of how modifying BA characteristics affects or ameliorates disease.