Association Between Vitamin D Deficiency and Bone Mineral Density in Type 2 Diabetes: A cross-sectional study

Background: People with type 2 diabetes mellitus (T2DM) sustain more fractures than peers despite often normal areal bone mineral density (BMD). Vitamin D deficiency is common in South Asia and may worsen diabetic skeletal fragility. Objectives: To assess the association between serum 25-hydroxyvitamin D [25(OH)D] and BMD in adults with long-standing T2DM. Methods: A Multicenter cross-sectional study at two tertiary hospitals in Punjab, Pakistan was conducted. Current study enrolled 110 adults aged 40–75 years with T2DM duration ≥5 years. Fasting 25(OH)D was measured by LC–MS/MS. Lumbar-spine (L1–L4) and femoral-neck BMD were measured by DXA. Multivariable linear models related 25(OH)D (per 10-ng/mL and categories: deficient <20 ng/mL; insufficient 20–29; sufficient ≥30) to site-specific BMD, adjusting for age, sex, BMI, diabetes duration, HbA1c, eGFR, lifestyle factors, diet, and thiazolidinedione use. Results: Participants were 57.2±8.6 years; 52.7% women; BMI 28.9±4.7 kg/m²; diabetes duration 10.5 years. Vitamin D deficiency and insufficiency were present in 62.7% and 24.5%. Each 10-ng/mL higher 25(OH)D associated with +0.029 g/cm² (95% CI 0.014–0.044) lumbar and +0.025 g/cm² (0.011–0.039) femoral-neck BMD. Versus sufficiency, deficiency associated with −0.071 and −0.056 g/cm² lower lumbar and femoral-neck BMD; insufficiency showed intermediate deficits. Associations were stronger in women and in participants with HbA1c ≥8%; no strong nonlinearity was detected. Conclusions: Lower 25(OH)D independently relates to lower axial and femoral BMD in T2DM. Integrating vitamin D evaluation and correction into diabetes bone care is clinically prudent while fracture-endpoint trials are pursued.