Greater urinary calcium excretion is associated with diminished bone accrual in youth with type 1 diabetes

Context: The adverse skeletal effects of type 1 diabetes (T1D) include deficient bone accrual and lifelong increased fracture risk. The contributors to impaired bone accrual in people with T1D are incompletely understood.

Objective: To determine if urinary calcium excretion is associated with impaired bone accrual in youth with T1D and to characterize the contribution of glycemic control and markers of bone mineral metabolism to urinary calcium excretion.

Design: Observational study.

Participants: 50 participants with T1D aged 6-20 years completed a 12-month longitudinal study of bone accrual. A second cohort of 99 similarly aged participants with T1D completed cross-sectional 24-hr urine and blood collections.

Main outcome measure: Whole body less head bone mineral content (WBLH BMC) velocity Z-score and fractional excretion of calcium (FeCa).

Results: Participants in the bone accrual cohort had lower WBLH BMC velocity compared to a healthy reference dataset (Z-score -0.3 ± 1.0, p=0.03). FeCa was negatively associated with WBLH BMC velocity Z-score, ρ= -0.47, p=0.001. In the urinary calcium excretion cohort, intact parathyroid hormone (β= -0.4, p=0.01), beta c-telopeptide (β=0.35, p=0.007), and either hemoglobin A1c (HbA1c, β=0.08, p=0.03) or urine fractional glucose excretion (β=0.07, p=0.03) were associated with FeCa in multivariable regression models that included known determinants of urinary calcium excretion.

Conclusions: Urinary calcium excretion was negatively associated with bone accrual in this cohort of youth with T1D. Mechanistic studies are needed to determine if interventions to reduce urinary calcium excretion could increase bone accrual and reduce skeletal fragility in people with T1D.