Serum 25-hydroxyvitamin D is associated with islet function in postmenopausal women with type 2 diabetes and osteoporosis.

BACKGROUND

To evaluate the association between serum 25-hydroxyvitamin D [25(OH)D] levels and islet function in postmenopausal women with type 2 diabetes mellitus (T2DM) and osteoporosis.

METHODS

A total of 343 consecutively hospitalized postmenopausal women with type 2 diabetes mellitus and osteoporosis between December 2024 and December 2025 were included in the final analysis. Participants were classified into three groups according to serum 25(OH)D levels: sufficiency (>30 ng/mL), insufficiency (20-30 ng/mL), and deficiency (<20 ng/mL). Clinical characteristics, bone mineral density, and islet function-related indices were compared among the groups. Spearman correlation analysis and multivariable linear regression were performed to evaluate the associations between serum 25(OH)D levels and islet function.

RESULTS

No significant differences were found among the three groups in age, duration of T2DM, or glycated hemoglobin (HbA1c) (all P > 0.05), whereas body mass index (BMI) showed a marginal overall difference among the groups (P = 0.047). Lumbar spine, femoral neck, and total hip T-scores were progressively lower across groups with lower serum 25(OH)D levels (all P < 0.001). Fasting insulin (FINS), fasting C-peptide (FCP), homeostasis model assessment of β-cell function (HOMA-β), and homeostasis model assessment of insulin resistance (HOMA-IR) also showed significant intergroup differences (all P < 0.001). Serum 25(OH)D was positively correlated with fasting insulin, fasting C-peptide, and HOMA-β, but negatively correlated with HOMA-IR (all P < 0.001). Multivariable analysis showed that serum 25(OH)D remained associated with islet function and insulin resistance after adjustment for age, BMI, HbA1c, and T2DM duration.

CONCLUSION

In postmenopausal women with type 2 diabetes mellitus and osteoporosis, lower serum 25(OH)D levels were associated with poorer β-cell function, greater insulin resistance, and lower bone mineral density.