Liver enzymes and vitamin D levels in metabolically healthy but obese individuals: Korean National Health and Nutrition Examination Survey

Abstract

Objective

Increased liver enzymes and decreased vitamin D levels are associated with insulin resistance and type 2 diabetes. We examined liver enzymes and vitamin D levels in metabolically healthy but obese (MHO) individuals and compared the values with those of other body size phenotypes in the Korean population.

Materials/Methods

A total of 16,190 people over the age of 18 years were analyzed using data from the Fourth Korean National Health and Nutrition Examination Survey, which is a nationally representative survey. Body size phenotypes were classified into four groups by body mass index (BMI) and number of metabolic syndrome components.

Results

The prevalence of MHO was 14.9% in the entire population and 47.7% in the obese population. In a correlation analysis adjusted for age, sex, and BMI, AST and ALT levels were positively correlated with insulin resistance and cardiometabolic risk factors of the metabolic syndrome, whereas vitamin D level was negatively correlated with these variables. MHO individuals had significantly lower concentrations of AST and ALT compared to metabolically abnormal obese (MAO) subjects, although vitamin D levels were not significantly different. Furthermore, a multiple logistic regression analysis revealed that MHO individuals had lower risk of liver enzyme abnormality compared to MAO after adjusting for potential confounding factors. However, the risk of vitamin D deficiency was not significantly different among groups with different body size phenotypes.

Conclusions

Although both liver enzymes and vitamin D levels are related to insulin resistance and metabolic syndrome, only liver enzymes were independently associated with MHO phenotype.

Introduction

Metabolically healthy but obese (MHO) individuals comprise a subset of the obese population, and they have drawn attention due to their unique metabolic features. These individuals, despite having excessive body fat, display a favorable metabolic profile, including high insulin sensitivity, normal lipid and blood pressure, and low circulating inflammatory markers [1], [2], [3]. Calori et al. reported that MHO individuals did not show increased all-cause, cancer, or cardiovascular disease (CVD) mortality compared with non-obese insulin-sensitive subjects in a 15-year follow-up study [4].

Obesity is closely associated with nonalcoholic fatty liver disease (NAFLD), which is a hepatic manifestation of metabolic syndrome [5]. Stefan et al. found that ectopic fat in skeletal muscle and particularly the liver was lower in the obese–insulin-sensitive group than in the obese–insulin-resistant group [6]. In a recent study of 103 postmenopausal Caucasian women, Messier et al. reported that MHO individuals, defined by insulin sensitivity index, had significantly lower concentrations of liver enzymes than insulin-resistant at-risk subjects [7]. However, the relationship between liver enzymes and MHO phenotype has not been established in other age groups or ethnicities.

Vitamin D has numerous functions beyond calcium and bone metabolism. The cross-sectional survey of the Third National Health and Nutrition Examination Survey in the United States (NHANES III) showed an inverse relationship between vitamin D level and diabetes, possibly involving insulin resistance, in non-Hispanic whites and Mexican Americans [8]. Moreover, there was an inverse relationship between serum concentration of vitamin D and the prevalence of metabolic syndrome [9]. Recently, Barchetta et al. reported that low 25-hydroxyvitamin D (25(OH)D) level is associated with the presence of NAFLD, independent of metabolic syndrome, diabetes and insulin-resistant profiles [10]. However, to the best of our knowledge, no previous studies have explored vitamin D level in MHO individuals.

The present study examined concentrations of liver enzymes and vitamin D in MHO individuals and compared them with those of other body size phenotypes using representative data from the Fourth Korean National Health and Nutrition Examination Survey (KNHANES IV).