A-130 Triglyceride–Glucose (TyG) Index Outperforms Glycemic Status Alone in Predicting Vitamin D Deficiency among Obese Egyptian Adults

Abstract

Vitamin D deficiency is highly prevalent in obesity and has been linked to insulin resistance, atherogenic dyslipidemia, and increased cardiometabolic risk. Whether vitamin D deficiency in obese individuals is driven predominantly by glycemic category (euglycemia, prediabetes, type 2 diabetes mellitus T2DM) or by the underlying burden of insulin resistance and metabolic dysfunction remains uncertain. This study evaluated the association between serum 25-hydroxyvitamin D 25(OH)Dand a panel of insulin resistance surrogates and metabolic risk indices across the glycemic spectrum in obese Egyptian adults. In a cross-sectional study, 410 adults aged 35–55 years were categorized into four groups: healthy controls (n = 100), euglycemic obese (n = 125), prediabetic obese (n = 85), and T2DM obese (n = 100). Clinical and biochemical evaluation included BMI, fasting plasma glucose, HbA1c, fasting insulin, lipid profile, and serum 25(OH)D. Insulin resistance surrogates (HOMA-IR, TyG, TyG–BMI, Metabolic Score for Insulin Resistance (METS IR), hemoglobin glycation index) and lipid-based ratios (non HDL-C/HDL-C, TG/HDL-C) were calculated. Pearson correlations examined associations between 25(OH)D and metabolic markers in obese groups. Principal component analysis (PCA) explored multivariate clustering of metabolic risk variables.Among obese participants (n = 310),binary logistic regression identified independent predictors of moderate–severe vitamin D deficiency, defined as 25(OH)D < 15 ng/mL, adjusting for age, sex, and glycemic category. Vitamin D deficiency was highly prevalent in all obese groups, with significantly lower 25(OH)D concentrations in euglycemic, prediabetic, and T2DM obese participants than in controls (p < 0.001), and the lowest levels observed in T2DM obese (10.0 ± 4.53 ng/mL). Obese groups showed progressive worsening of fasting glucose, HOMA-IR, and atherogenic lipid indices compared with controls (p < 0.001) respectively, with prediabetic obese individuals exhibiting particularly adverse TG/HDL-C, non HDL-C/HDL-C, and METS IR profiles. Across obese subgroups, serum 25(OH)D correlated inversely with fasting plasma glucose, triglycerides, TG/HDL-C, and TyG (p < 0.05) respectively, indicating a tight link between low vitamin D status, insulin resistance, and dyslipidemia. PCA demonstrated a clear metabolic gradient from controls to euglycemic obesity, and T2DM, with low 25(OH)D clustering alongside higher HOMA IR, METS IR, and adverse lipid markers, independently of glycemic category. In multivariable logistic regression, the TyG index emerged as a strong independent predictor of moderate–severe vitamin D deficiency (odds ratio 5.66, p < 0.001), whereas METS IR and glycemic category (prediabetes or T2DM vs euglycemic obesity) were not independently associated. In obese Egyptian adults, vitamin D deficiency is more strongly linked to the severity of insulin resistance and atherogenic dyslipidemia than to glycemic category alone.The TyG index, an inexpensive and insulin free surrogate of insulin resistance, outperforms glycemic status in identifying obese individuals at heightened risk of vitamin D deficiency,including those in the prediabetic “transition” stage.These findings support incorporating simple IR related indices such as TyG into risk stratification strategies for vitamin D deficiency and cardiometabolic risk in obesity.Longitudinal studies are warranted to clarify causality and determine whether targeting insulin resistance can favorably modify vitamin D status and downstream metabolic outcomes.