Visceral Adiposity Index and Leptin Levels in Type 2 Diabetics in Port Harcourt: Effects of Disease Duration and Sex

Abstract

Background: Diabetes mellitus (DM) is a group of endocrine diseases, resulting from insufficient or improper use of insulin. It is characterized by prolonged high blood sugar levels. The exponential increase in DM poses serious public health concerns. Again, obesity is a complex condition with substantial accumulation of excess total body fat (visceral and subcutaneous) that could impact health. Visceral fat previously thought to be inert, has been found to be an endocrine organ, that produces adipokines such as leptin and adiponectin, which regulate several body functions including metabolism, inflammation, appetite, cardiovascular function and immunity. Visceral adiposity index (VAI), a sex specific mathematical model which indicates fat distribution and function, is a better indicator for obesity, as opposed to body mass index (BMI), which cannot differentiate between subcutaneous and visceral fat, making it a valuable tool for assessing metabolic dysfunction in diabetes. Aim: This study evaluated visceral adiposity index (VAI) and leptin levels in type 2 diabetic subjects in Port Harcourt, Nigeria, highlighting the effect of disease duration and sex differences. Materials and Methods: A cross-sectional study design was adopted for the study. A total of 225 participants were involved in the study. This was made up of 125 type 2 diabetic (test) subjects and 100 non-diabetic (control) subjects.  Subjects observed an overnight fast prior to sample collection. Fasting blood sugar (FBS) was determined using the glucose oxidase method. Glycated haemoglobin (HbA1c) was determined using the electrochemical piezoelectric sensor method. Fasting insulin and leptin were determined using the enzyme–linked immunosorbent assay (ELISA) method. Insulin resistance was determined using the homeostatic model assessment for insulin resistance (HOMA-IR) method. Triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) were determined by the enzymatic method. Body mass index (BMI) was determined with the formula: BMI = weight (kg) / height² (m²). Waist to hip ratio (WHR) was determined with the formula: WHR= Waist circumference (WC) (cm) / Hip Circumference (HC) (cm). Visceral adiposity index (VAI) was determined with the formula: VAI = [WC/39.68 + (1.88 × BMI)] × (TG/1.03) × (1.31/HDL) for men, and [WC/36.58 + (1.89 × BMI)] × (TG/0.81) × (1.52/HDL) for women. Data generated was analysed using GraphPad Prism version 8.0.2. Independent student’s t-test, analysis of variance (ANOVA) and Tukey Post-test were done where necessary. Pearson’s correlation was also used to correlate parameters. Results were considered significant at a 95% confidence interval (P ≤ 0.05). Results: HbA1c, FBS, insulin and HOMA-IR were significantly higher (P<0.05) in the diabetics, compared to the controls. Leptin levels, VAI, BMI and WHR of the diabetics were significantly higher (P<0.05), compared to the controls. Leptin levels were significantly higher (P<0.05) in the female diabetics, compared to the male diabetics. There were no significant differences (P>0.05) in HOMA-IR and WHR between the male and female diabetics. VAI and BMI were significantly higher (P<0.05) in the female diabetics, compared to their male counterparts. There were no significant differences (P>0.05) in leptin levels, HOMA-IR, VAI, HbA1c and BMI in subjects with diabetes for 1 – 5 years, 6 – 10 years and those with diabetes for 11 years and above. Leptin was positively correlated with insulin (r=0.363), insulin resistance (r=0.540) and VAI (r=0.210). There was a significant (P<0.05) and positive correlation between leptin and WHR (r=0.229), and leptin and BMI (r=0.238). VAI (r=0.698) and WHR (r=0.638) were significantly (P<0.05) and positively correlated with insulin resistance (HOMA-IR). Conclusion: Type 2 diabetes is associated with visceral fat accumulation, hyperleptinaemia, and leptin resistance. Sex differences contributed significantly to elevated VAI, BMI and leptin levels in the female diabetics, compared to the male diabetics. Disease duration had no effect on the parameters, as leptin, VAI, BMI, HOMA-IR and HbA1c remained elevated throughout the duration of diabetes. VAI and leptin estimation should be incorporated into routine clinical assessments as reliable biomarkers for insulin resistance and metabolic dysfunction.