Objective: Obesity has become a public health problem and its incidence is increasing rapidly worldwide. It is a well-known risk factor for metabolic and cardiovascular diseases and closely related to insulin resistance the mechanism of which is not exactly understood. Obesity cause a low grade inflammatory state, increase in adipose-specific cytokines, immune cell infiltration and disrupted function of tissues involved in glucose homeostasis (1). Insulin resistance refers to the resistance to actions of insulin hormone in peripheral tissues. This may be the result of impaired insulin signaling and/or downregulation of insulin receptors on cell membrane. Evaluation of insulin resistance in daily practice generally requires sophisticated methods. Homeostatic model assessment of IR (HOMA-IR) is commonly used parameter for evaluation of insulin resistance and its calculation is based on measurement of glucose and insulin levels. Since insulin levels are not routinely calculated, other parameters that could be helpful in determining the insulin resistance have been developed. Triglyceride-glucose index (Tyg index) is a novel surrogate marker for detecting insulin resistance in various clinical conditions. Its calculation requires serum triglyceride (TG) and glucose levels. Several studies showed its relation with type 2 diabetes mellitus, hypertension, metabolic syndrome, intima media thickness and chronic kidney disease (2-6). Furthermore it could be used as a measure of insulin sensitivity in obese subjects (7). The present study was aimed to evaluate Tyg index in overweight and morbid obese subjects and to test whether there was a difference between two groups of subjects.
Materials and Methods: This retrospective study enrolled 40 overweight and 39 morbid obese subject. Individuals with diabetes mellitus, hypertension, thyroid function abnormalities, renal and/or hepatic insufficiency, malignancy and active infection were excluded from the study. Body mass index (BMI) was calculated from self-reported height and weight with the use of following formula: weight (kg) / height (m)2. Subjects who had BMI values between 25-30 kg/m2 and >40 m2 were classified as overweight and morbid obese, respectively. Group 0 composed of overweight subjects, group 1 composed of morbid obese patients. Biochemical analysis results of the participants were obtained from hospital database. Venous blood samples of the subject were drawn after an overnight fast. Parameters including fasting glucose, HOMA-IR, high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), TG, uric acid, c-reactive protein (CRP) were measured. Tyg index was calculated as ln (fasting triglycerides × fasting glucose / 2).
Statistical analysis: Normality of the data was assessed by using Kolmogorov-Smirnov test. Comparison of the parametric and non-parametric data was done by independent samples t-test and Mann-Whitney U test, respectively. Correlation of the parameters was assessed by Spearman correlation analysis. A p value of less than 0.05 was considered as significant.
Results: Mean age of the overweight and morbid obese subjects were 33.28±12.89 years and 35.08±11.78 years, respectively. BMI of overweight group was 28.00 ±1.36 kg, morbid obese group was 44.51±4.11 kg. There were no differences with respect to values of glucose, HDL-C, LDL-C, TG between two groups. HgA1c, HOMA-IR, uric acid, CRP levels of the morbid obese subjects were higher than that of the overweight subjects. Table 1 shows the clinical characteristics of two groups. There was no difference in Tyg index values of two groups. Although Tyg index showed a positive correlation with BMI in overweight subjects (p=0.013, r=0.389), we did not find any correlation between two parameters in morbid obese group (p=0.316, r=0.165). Uric acid and HOMA-IR showed positive correlation with BMI (p=0.004, r=0.340 and p=0.001, r=0.352, respectively).
Discussion: Obesity is closely related to insulin resistance which is a risk factor for metabolic syndrome, type 2 diabetes and cardiovascular disease. Predictive value of BMI for identification of impaired fasting glucose and impaired glucose tolerance was found to be as 0.61 and 0.60, respectively (8). Man et al. showed that each one unit increase of BMI is associated with an increased incidence of prediabetes by 6%. Moreover, BMI values of greater than 27.5 kg/m2 increased the risk of prediabetes by 61% (9). Cardiometabolic risk scores and HOMA-IR levels were found to be positively correlated with BMI (10). In this context we wanted to evaluate HOMA-IR and Tyg index values of morbid obese subjects in order to evaluate the value of this parameter in this group of subjects. According to our results Tyg index did not differ between overweight and morbid obese subjects. However HOMA-IR levels were found to be statistically significantly higher in morbid obese group. Although Tyg index did not show any correlation with BMI; when two groups were evaluated separately, it showed significant although weak correlation in overweight subjects. Our results suggested that Tyg index might not be a valuable tool for the assessment of insulin resistance in morbid obese subjects.
Anahtar Kelimeler: triglyceride-glucose index, morbid obese, overweight, insulin resistance
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