[An Overview of NAFLD/NASH in Japan]

Clinical identity of nonalcoholic steatohepatitis (NASH) has established it as a chronic liver disease since the 1990s in the USA and in the 21st century in Japan, although its significance is not well recognized in Japanese society. It is characterized as a chronic liver disease, differentiated from viral liver disease and alcoholic liver disease. Nonalcoholic fatty liver disease (NAFLD) comprises nonalcoholic fatty liver (NAFL) and NASH. NASH is considered to be the hepatic manifestation of a metabolic syndrome. It is understood that among individuals with NAFLD, NAFL is a benign condition, whereas NASH can progress to cirrhosis and ultimately to hepatocellular carcinoma. The precise mechanism of NASH is poorly understood, although insulin resistance, oxidative stress and multiple parallel hits theory have been reported. Computed tomography and ultrasonography are performed to detect NAFLD, but these are not sufficient to distinguish between NAFL and NASH. The distinct diagnosis of NAFL and NASH is currently made by liver biopsy, requiring hospitalization. Therefore, there is an urgent need to develop simple, non-invasive markers that can accurately distinguish between NASH and NAFL. In Japan, the number of NASH patients is estimated to be about 1 million. The treatment of NASH comprises changes in life style, including eating habits and exercise that will lead to weight loss, and drug intake, including vitamin E. Based on the global increase in obese people, NASH as a chronic liver disease will become the most important chronic liver disease in the 21st century, not only in Japan but also worldwide.