Non-alcoholic Fatty Liver Disease as an Independent Manifestation of the Metabolic Syndrome

Results of a US National Survey in Three Ethnic Groups

Mark M Smits; George N Ioannou; Edward J Boyko; Kristina M Utzschneider

Disclosures

J Gastroenterol Hepatol. 2013;28(4):664-670. 

In This Article

Abstract and Introduction

Abstract

Background and Aim: The metabolic syndrome (MetS) and each of its components are strongly associated with non-alcoholic fatty liver disease (NAFLD). This has led many investigators to suggest that NAFLD is an independent component of the MetS. We formally tested this hypothesis using confirmatory factor analysis, which allows comparison of different models, with or without including NAFLD as a component of the MetS.

Methods: We analyzed data from 3846 subjects of the Third National Health and Nutrition Examination Survey (1988–1994). NAFLD was defined by increased liver fat measured by ultrasonography.

Results: MetS by Adult Treatment Panel III criteria was present in 20.5%, and 30.2% had NAFLD, defined as mild, moderate, or severe ultrasonographic steatosis. Using confirmatory factor analysis, a basic model representing the MetS using its currently accepted components (glucose, waist, triglyceride/high-density lipoprotein ratio, and mean arterial pressure) showed excellent goodness-of-fit statistics. Addition of NAFLD to the model as a fifth independent variable decreased model fit, suggesting that NAFLD is not an additional independent component of the MetS. Analysis by ethnicity showed that addition of NAFLD decreased model fit in Whites but resulted in minor improvements in non-Hispanic Blacks and Mexican Americans.

Conclusions: The MetS is strongly associated with NAFLD. However, we found no evidence that NAFLD is an independent component or manifestation of the MetS. Interestingly, ethnic differences might be important in this relationship and require further study.

Introduction

The metabolic syndrome (MetS) represents a clustering of five cardiometabolic risk factors known to increase the risk of type 2 diabetes and cardiovascular disease.[1,2] The pathophysiology underlying this clustering is not clearly defined, but obesity and insulin resistance are considered major factors.[3,4] Non-alcoholic fatty liver disease (NAFLD) is the accumulation of fat in the liver in the absence of excessive alcohol consumption[5] and is strongly associated with obesity and insulin resistance.[6] The MetS, as well as each of its five components, are strong risk factors for the presence of NAFLD.[7–10] This has led investigators to suggest that NAFLD is a component of the MetS, and it is frequently quoted that "NAFLD is the hepatic manifestation of the MetS."[11,12]

However, the fact that the MetS is strongly associated with NAFLD does not prove that NAFLD is a component of the MetS. To our knowledge, the hypothesis that NAFLD is a component of the MetS has not been formally tested using appropriate statistical methodology. Our aim was to test whether NAFLD is a component of the MetS using confirmatory factor analysis (CFA). CFA is a mathematical technique that allows the researcher to specify and test the plausibility of different models of the MetS that include different underlying components.[13] Using CFA, it has been shown that the features of the MetS cluster on one underlying variable, often referred to as the "pathophysiology" of the MetS.[14,15] CFA uses the dataset to analyze the validity of a specified model and expresses this in "goodness-of-fit" parameters. We aimed to investigate whether NAFLD is an additional independent component of the MetS by comparing the "goodness-of-fit" of models of the MetS with and without hepatic steatosis.

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