The Epidemiology of Nonalcoholic Fatty Liver Disease: A Global Perspective

Mariana Lazo, M.D., M.Sc.; Jeanne M. Clark, M.D., M.P.H.

Disclosures

Semin Liver Dis. 2008;28(4):339-350. 

In This Article

Abstract and Introduction

Abstract

Nonalcoholic fatty liver disease (NAFLD) is an increasingly recognized cause of liver disease in the United States and worldwide. With obesity being an important risk factor universally, NAFLD is now receiving greater attention and is regarded as a public health issue. In addition, as a result of an aging population and the improving control of other major causes of chronic liver disease, such as hepatitis C and hepatitis B, the burden of NAFLD is expected to increase in years to come. Prevalence estimates of this disease vary widely across populations because of differences in methods for diagnosis and/or definition. New strategies for the prevention, diagnosis, and management will be required to alter the course of this disease.

Introduction

Nonalcoholic fatty liver disease (NAFLD) is a broad term used to encompass an entire spectrum of liver disease ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), which can eventually lead to nonalcoholic, noncholestatic cirrhosis and probably hepatocellular carcinoma.[1,2,3] Although, histologically NAFLD resembles alcohol-induced liver disease, by definition NAFLD develops in patients who consume little or no alcohol. Based on the etiology, NAFLD is subdivided into primary and secondary. The primary type is commonly found among people with conditions such obesity, type 2 diabetes, and metabolic syndrome, and is thought to be caused by insulin resistance. The secondary type can be associated with the use of certain medications and a variety of miscellaneous disorders that include infectious, nutritional, and inborn errors of metabolism.[4] An adequate review of all the causes of NAFLD listed is beyond the scope and intent of this article and was recently published.[5] In this article we will focus on the epidemiology of primary NAFLD.

For many years, alcoholic liver disease and viral hepatitis-induced liver disease were considered the main causes of liver disease morbidity and mortality in the United States and elsewhere in the world. However, with the dramatic increase in the prevalence of obesity, NAFLD has become the most common chronic liver disease and is now receiving greater attention globally. At the beginning of this 21st century more than 30% of the U.S. population is obese; globally, there are at least 400 million obese adults in low-, middle- and high-income countries.[6] Previous studies have estimated that ~75% percent of those with obesity have NAFLD, and up to 20% may have NASH.[7,8]

Epidemiologic studies are the foundation for disease control and prevention by tracking the prevalence of the disease, characterizing the natural history and identifying determinants of the disease. Beyond that, epidemiologic studies are also utilized to assess diagnostic methods and to evaluate interventions. Our objective is to provide the clinician with a summary of the most recent epidemiologic evidence on NAFLD in the United States and throughout the world. Other essential aspects of NAFLD are covered elsewhere in this issue of Seminars of Liver Disease.

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