Epidemiology of Non-alcoholic Fatty Liver Disease in the Asia-Pacific Region

Jiangao Fan  Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China

Non-alcoholic fatty liver disease (NAFLD) is among the most common causes of chronic liver disease in the Western world. However, obesity and metabolic syndrome (MetS), the common substrates of NAFLD are not restricted to the West, as witnessed by their increasingly universal distribution. Based particularly on large community-based studies, the prevalence of US-defined NAFLD in the general population ranges from 9% to 30% in Asia, depending on age, gender, locality, ethnicity, and the time of the survey performed (Lazo M, Clark JM. Seminars Liver Dis 2008; 28:339-350). There is strong evidence that the prevalence of NAFLD has increased recently in parallel with regional trends in obesity, type 2 diabetes, and MetS; and that further increases are likely. The relationship between NAFLD and MetS is clearly evident in retrospective and prospective Asian studies, but the strength of association with these metabolic risk factors is only appreciated when regional definitions of ethnic-specific definitions are used. Moreover, NAFLD patients with normal body weight seem to more common in Asians than Caucasians. NAFLD appears to be associated with long-standing insulin resistance and likely represents the hepatic manifestation of MetS. Not surprisingly therefore, Asians with NAFLD are at high risk of developing both hepatic (cirrhosis and hepatocellular carcinoma) and extra-hepatic (diabetes and cardiovascular disease) complications in the long-term. Therefore, NAFLD is also emerging into a new and major health problem in Asia-Pacific region, and the magnitude of the problem is comparable to Western countries.

In China, fatty liver is highly prevalent in residents of affluent, industrialized regions, and is more often linked to obesity than to alcoholism. With the increasing pandemic of obesity, the prevalence of NAFLD has approximately doubled in the past decade. The full range of histological manifestations of NAFLD has been demonstrated in Chinese patients, but to date hepatic severity is generally mild. In contrast to chronic hepatitis C, hepatic steatosis is less common in patients with chronic hepatitis B infection; it is associated with metabolic factors not viral ones, and does not appear to affect disease severity of hepatitis B. Although long-term outcomes of NAFLD in Chinese populations remain unclear, it may be a predictor of metabolic disorders, diabetes and cardiovascular disease (Fan JG, Farrell GC. J Hepatol 2009; 50: 204-210).

There are few published data on the incidence of NAFLD worldwide. The incidence of US-defined NAFLD in 3147 healthy Japanese men with a mean age 48 years after a mean follow-up of 414 days was found to be 9.8% (Hamaguchi M, et al. Ann Intern Med 2005; 143:44-52). In a more recent study, Fan, et al. prospectively investigated the incidence of NAFLD among 5626 employees (4437 men, mean age 36 years) of Bao-Steel company (Shanghai, China). The incidence of NAFLD was found to be 6.2% in the overall population with no significant difference between men and women (6.4% vs. 4.7%) during the 2-year follow-up. The baseline level of body weight, serum triglyceride, and their subtle gains during follow-up are independent predictors of incident NAFLD (Unpublished data).