Causes of Mortality in Non-Alcoholic Fatty Liver Disease (NAFLD) and Alcohol Related Fatty Liver Disease (AFLD)

Non-alcoholic fatty liver disease (NAFLD) and alcohol related fatty liver disease (AFLD) both represent a spectrum of liver disease severity from hepatic steatosis to fibrosis and cirrhosis. Both NAFLD and AFLD are common diseases in the general population. NAFLD affects ~25% of the adult global population whilst AFLD has become the commonest indication for liver transplantation in the United States. It is often not possible to distinguish between NAFLD and AFLD on examination of liver histology, consequently, differentiation between NAFLD and AFLD is heavily reliant on a history of alcohol consumption. Age, smoking, alcohol consumption and sex appear to influence the risk of mortality in NAFLD or AFLD. In NAFLD and AFLD, the key causes of increased liver-related mortality are advanced liver fibrosis and cirrhosis leading to complications such as hepatocellular carcinoma and decompensated cirrhosis. NAFLD and AFLD are also associated with an increased risk of all-cause mortality including an increased risk of extra-hepatic malignancy. Non-invasive biomarkers of liver disease severity in NAFLD and AFLD perform poorly to predict mortality. However, alanine aminotransferase, gamma-glutamyl transpeptidase, FIB-4 and the NAFLD Fibrosis Score are independently associated with increased mortality in NAFLD. Both NAFLD and AFLD are associated with extra-hepatic risk factors and complications such as metabolic syndrome encompassing obesity, hypertension, type 2 diabetes mellitus, and chronic kidney disease. AFLD is associated with hypertension and cardiovascular disease as well as other organ damage. This narrative review discusses the associations, risk factors and diagnostic biomarkers linking NAFLD and AFLD with increased mortality.