The Chinese University of Hong Kong (CUHK) has engaged in many epidemiological studies aiming at portraying the severity of non-alcoholic fatty liver disease (NAFLD) in Hong Kong. Recently, it was revealed that NAFLD afflicts even the non-obese population and yielded a 19% of incidence from the community. Another study showed the prevalent clinical characteristics of non-obese patients with NAFLD. The first and the second studies were published in the American Journal of Gastroenterology1 and Hepatology2 respectively, and the results were announced by Professor Vincent Wong and Professor Grace Wong from the CUHK Faculty of Medicine.
Being the most commonly seen chronic liver disease globally, NAFLD afflicts 27% of the Hong Kong adult population3. NAFLD can be so devastating that it is the 2nd leading cause of liver transplant and the 3rd leading cause of liver cancer in the United States.3
Therefore, it is of paramount importance to understand this disease in even lean population, but as Professor Grace Wong highlighted, the understanding was scarce. “Though NAFLD rarely shows clinical symptoms, it may progress to steatohepatitis, cirrhosis, and hepatic carcinoma. NAFLD used to be associated with obesity, but it is now found in non-obese people as well. The epidemiology and clinical characteristics of this special group are poorly understood. Physicians are just beginning to learn more about NAFLD in the lean population.”3
To address this veiled field, the Faculty of Medicine in CUHK conducted two prospective, observational studies aiming at revealing the epidemiology of NAFLD in lean population. In the first study, 911 patients were recruited during 2006-2015, from the census database of the Hong Kong Government with their intrahepatic triglycerides (IHTG)1 and liver fibrosis assessed by proton-magnetic resonance spectroscopy and transient elastrography (FibroScan)3 respectively. When non-obese was defined as BMI≤25 kg/m2, 701 patients were found non-obese.1
It was found that around one-fifth (19%) of the general lean Chinese population suffers from NAFLD, but their severity of disease was generally lower than that of obese patients, as shown by the lower markers of liver injury (cytokeratin-18 fragments: 149 vs. 182 IU/l; p=0.019) and fibrosis (4.6 vs. 5.6 kPa; p<0.001). Moreover, enlarged waist circumference, elevated blood sugar (glycated hemoglobin level), insulin resistance, higher ferritin level, and the presence of polymorphism of the PNPLA3 gene were found to be the risk factors of NAFLD in non-obese patients.1
Professor Vincent Wong commented on the results. “To be frank, that one in five does have fatty liver is higher than expected. Based on the study, the risk of fatty liver goes up by 10 percent if a patient’s waist is just a centimeter larger. People are strongly advised to avoid soft drinks as the fructose content in them could induce fatty liver and make existing conditions worse.”4,5
While for the second study when 307 NAFLD patients were recruited during 2004-2015 and performed liver biopsy (72 were non-obese), non-obese patients had lower fibrosis stage (1.3 vs. 1.7, p=0.004). Nevertheless, these patients suffered from steatohepatitis (43.5% vs. 51.9%, p=0.217) and severe liver fibrosis (26.1% vs. 27.7%, p=0.791) in a similar rate comparing to the obese patients.2 It was also noted that after a median follow-up of 49 months, six patients died, two patients developed hepatocellular carcinoma, and one suffered from liver failure, all of whom belonged to the obese population.2
Professor Vincent Wong further elaborated the results. “Non-alcoholic steatohepatitis causes a faster progression into liver fibrosis while liver fibrosis can lead to cirrhosis or even cancer. But the non-obese fatty liver patients were less likely to develop life-threatening conditions in the average 49-month follow-up period.”Wong said.
“Nearly 20% of the people with BMI<25 still have NAFLD. Although non-obese patients tend to have less severe liver disease, they are still prone to developing steatohepatitis and liver fibrosis. Therefore, those with concurrent metabolic diseases should still undergo proper liver assessment,” Professor Vincent Wong concluded in the press release.3
The urge for people to undergo a liver assessment if they belong to risky populations was echoed by Professor Grace Wong. “People with normal build should undergo a proper liver assessment if they have concurrent metabolic problems, such as hypertension, high blood sugar, central obesity and high blood lipids.”4