Epidemiology and Natural History of Non-alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is an important cause of liver disease burden across the world. By definition, although the histopathologic features of NAFLD are identical to that of alcoholic liver disease, its diagnosis requires absence of significant alcohol use and absence of other causes of chronic liver disease. We now know that NAFLD is not simply a disease of the Western world. It is manifested across the world, in varying rates, across gender, across varying ethnicities, and in its association with other host factors. In this review article, the definition of NAFLD, its spectrum, ranging from mild steatosis to hepatocellular injury and inflammation defined as non-alcoholic steatohepatitis (NASH) is discussed. Mild steatosis is generally a stable disease whereas NASH can be progressive. Based on current published literature, current incidence and prevalence of NAFLD and NASH are discussed. It is also accepted that these processes will continue to increase in prevalence with the rise of obesity, type II diabetes, and associated metabolic syndrome. Some of the risk factors have been well-established and are discussed. In addition, this review also presents emerging associations with other risk factors for NAFLD. Natural history of NAFLD is variable depending upon the histologic subtypes and other underlying comorbidities and is discussed in this review as well.