Parathyroid hormone suppression and calcium homeostasis shift in type 2 diabetes with osteoporosis: a propensity score-matched cross-sectional study

The bone metabolic characteristics of type 2 diabetes mellitus (T2DM) with osteoporosis (OP) remain controversial. Previous studies often used “DM without OP” as comparison groups, but such groups may confound patients using antiresorptive drugs for bone metastasis. This study re-evaluates bone metabolism in DM + OP after excluding drug confounders and using propensity score-matched (PSM) pure DM comparison group. A retrospective cross-sectional study of hospitalized T2DM patients (2021–2024). The DM + OP group ( n = 461) excluded bone metastasis cases. From 21,181 pure DM patients without antiresorptive drugs, 1,383 were 1:3 PSM-matched on age and sex—selected as the two strongest confounders of bone metabolism given data availability. Serum bone turnover markers (beta-CTX, osteocalcin), 25(OH)VitD, PTH, calcium, and phosphorus were compared. HbA1c-stratified analysis was performed. After PSM, age (69.3 ± 8.8 years) and sex (15.2% male) were perfectly matched (SMD = 0.000). PTH was 22.6% lower in DM + OP vs. pure DM (40.3 vs. 52.0 ng/L, p < 0.001, Cohen’s d=-0.434), although both medians were within the reference range (15–65 ng/L). Serum calcium was statistically higher (2.21 vs. 2.20 mmol/L, p = 0.043), but the absolute difference (0.01 mmol/L) is unlikely to be clinically meaningful. Bone turnover markers (beta-CTX: 0.38 vs. 0.38 ng/mL, p = 0.580; osteocalcin: 12.0 vs. 11.0 ng/mL, p = 0.141) and 25(OH)VitD (24.7 vs. 22.8 ng/mL, p = 0.127) showed no significant differences. In pure DM, HbA1c-osteocalcin showed a moderate negative correlation ( r =-0.456, p < 0.001), while this correlation was weaker in DM + OP ( r =-0.206, p = 0.006). In this PSM-matched cross-sectional study of hospitalized T2DM patients, bone turnover markers showed no significant difference between DM + OP and pure DM comparison groups. Lower PTH concentrations in DM + OP were the most notable finding, though both groups’ median PTH remained within the normal range. The proposed mechanisms involving altered CaSR sensitivity or functional hypoparathyroidism remain unproven and require direct investigation. Since the study population consisted entirely of T2DM patients, these data cannot establish whether diabetes itself alters bone turnover. Future studies with BMD confirmation, renal function data, and longitudinal design are needed.