Relationships Among Adipose Tissue Distribution, Vitamin D, and Bone Metabolism in Normoglycemic and Type 2 Diabetic Individuals

Objectives: To investigate the interplay between adipose distribution, vitamin D metabolites, and bone mineral density (BMD) in Normal Glucose Tolerance (NGT) and type 2 Diabetic (T2DM) individuals. Methods: 167 participants (NGT: 61; T2DM: 106) were enrolled. Serum 25(OH)D, 1,25(OH)2D3, Parathyroid Hormone (PTH), and Ca were quantified. Visceral (VAT) and subcutaneous (SAT) adipose areas were assessed via dual bioelectrical impedance analysis. BMD and body composition were assessed via DXA. Metabolic indices (HOMA-IR, HOMA-β, ISI) were calculated. Results: 1. NGT: 25(OH)D was unrelated to adiposity. Conversely, 1,25(OH)2D3 was correlated inversely with VAT, SAT, body mass index (BMI), and Fat Mass Index (FMI), with VAT being the strongest independent predictor. 2. T2DM: High VAT correlated with insulin resistance yet paradoxically higher BMD. 25(OH)D correlated positively with Z-score, while 1,25(OH)2D3 correlated negatively with lumbar BMD. 3. VAT exerted a greater influence on insulin resistance than SAT, particularly in T2DM. Conclusions: 1. Visceral adiposity is the primary determinant of active 1,25(OH)2D3 metabolism in both NGT and T2DM individuals. 2. 1,25(OH)2D3 levels may be more closely associated with adiposity-related metabolic alterations than 25(OH)D. Despite lower 1,25(OH)2D3, the positive association between VAT and BMD in T2DM suggests complex mechanisms where visceral fat may paradoxically influence bone metabolism while driving insulin resistance.