Vitamin D deficiency is common in postmenopausal women with Type 2 diabetes mellitus (T2DM) and osteoporosis, but its relationship with islet function remains incompletely characterized. An observational study published in Frontiers in Endocrinology evaluated associations between serum 25-hydroxyvitamin D [25(OH)D] levels, β-cell function, insulin resistance, and bone mineral density in hospitalized postmenopausal women with T2DM and osteoporosis.

The analysis included 343 consecutively hospitalized postmenopausal women with T2DM and osteoporosis between December 2024 and December 2025. Participants were categorized according to serum 25(OH)D levels into sufficiency (>30 ng/mL), insufficiency (20-30 ng/mL), and deficiency (<20 ng/mL) groups. The study assessed clinical characteristics, bone mineral density, fasting insulin and C-peptide levels, and homeostasis model assessment indices for β-cell function (HOMA-β) and insulin resistance (HOMA-IR).

Findings

• Lumbar spine, femoral neck, and total hip T-scores progressively declined across groups with lower serum 25(OH)D levels (all P<0.001).
• Fasting insulin, fasting C-peptide, HOMA-β, and HOMA-IR differed significantly between vitamin D groups (all P<0.001).
• Serum 25(OH)D levels were positively correlated with fasting insulin, fasting C-peptide, and HOMA-β, while inverse correlations were observed with HOMA-IR (all P<0.001).
• Multivariable analyses showed that associations between serum 25(OH)D levels, islet function, and insulin resistance remained significant after adjustment for age, body mass index, glycated hemoglobin (HbA1c), and T2DM duration.

The findings suggested that lower serum 25(OH)D levels were associated with poorer β-cell function, greater insulin resistance, and lower bone mineral density in postmenopausal women with T2DM and osteoporosis.