Evidence of disordered calcium metabolism in adolescent girls with type 1 diabetes: An observational study using a dual-stable calcium isotope technique.

Type 1 diabetes (T1D) is associated with skeletal abnormalities including low bone density and increased fracture risk. The pathophysiology underlying T1D related skeletal fragility remains unknown. The objective of this study was to use a dual-stable calcium isotope method to investigate the effects of T1D on calcium absorption and estimated calcium retention in adolescent females. Twenty adolescent females with T1D were admitted for a 24-h calcium absorption study using oral (44 Ca) and intravenous (42 Ca) stable isotopes for determination of percent gastrointestinal calcium absorption and estimated calcium retention. Five out of twenty participants were found to have negative estimated calcium retention. Participants with negative calcium retention had greater urinary calcium excretion [202mg/d (IQR: 178-213)] compared to those with positive calcium retention [101.5mg/d (IQR: 82-122)], p=0.01, but similar calcium intake and percent calcium absorption. With the exception of one outlier, 24-h urine calcium was significantly associated with hemoglobin A1c (Pearson's r=0.55, p=0.02). 50% of participants consumed less than the RDA for calcium; fractional calcium absorption was inversely correlated with calcium intake in participants not meeting the RDA (Spearman's rho -0.65, p=0.04). In conclusion, one-quarter of adolescent girls with T1D were found to have negative estimated calcium retention at a time when bone mineral accrual should be ongoing. This appeared to be the result of excess urinary calcium excretion as opposed to diminished gastrointestinal calcium absorption. Insufficient calcium availability for bone deposition during adolescence could impair bone mineral accrual and contribute to skeletal fragility. Trial registered: ClinicalTrials.gov Reg No. NCT03156179.