Type 1 diabetes associated with excess urinary calcium excretion in adolescent girls
Researchers observed excess urinary calcium loss in a small group of adolescent girls with type 1 diabetes, suggesting diminished calcium retention in these patients and a possible increased risk for fracture, according to findings published in Bone.
“Our results did not identify an adverse effect of [type 1 diabetes] on gastrointestinal calcium absorption, but did suggest that excess urinary calcium excretion during adolescence may contribute to whole body calcium loss during a time when bone mineral accretion is expected to be ongoing,” David R. Weber, MD, MSCE, of the department of pediatrics at Golisano Children’s Hospital and the University of Rochester School of Medicine and Dentistry, and colleagues wrote. “Because lower bone mass is associated with greater fracture risk, optimizing bone accrual and peak bone mass is a critical aspect of skeletal health.”
In a cross-sectional study, Weber and colleagues analyzed data from 20 girls aged 9 to 16 years with type 1 diabetes for at least 3 years and at Tanner stage 2 or greater breast development, recruited from the pediatric endocrinology clinic at the University of Rochester (median age, 14 years; median diabetes duration, 5.6 years; mean HbA1c, 9%). Between August 2015 and December 2016, participants were admitted for a 24-hour calcium absorption study using both oral and IV calcium stable isotopes to determine the percentage of gastrointestinal calcium absorption and estimated calcium retention. All girls provided fasting blood samples and received 2 mg calcium infusion for 5 minutes, followed by a 5-mL saline flush. With breakfast, participants consumed 30 mL milk or calcium-fortified orange juice containing 7 mg calcium. A complete 24-hour urine collection followed in 8-hour intervals. All participants completed a 3-day food diary before their study visits to estimate typical calcium intake. Researchers calculated percent dietary calcium absorption as the ratio of the cumulative recovery of oral calcium to the cumulative recovery of IV calcium in the 24-hour urine sample. True calcium absorption was calculated as the product of fractional calcium absorption and dietary calcium intake, in which dietary calcium intake was the average of calcium intake at home and from the weighed-food record.
Within the cohort, five patients reported a history of fracture and 20% were deficient in 25-hydroxyvitamin D. Dietary calcium intake was lower than the recommended daily allowance of 1,300 mg per day in 50% of participants, and the median percent calcium absorption and true calcium absorbed were 26.6% and 277.9 mg per day, respectively. There were no between-group differences by pubertal status.
Five participants had an estimated calcium retention value of less than 0, all of whom were Tanner stage 4 or 5. These participants also had a urinary calcium excretion (mean, 202 mg per day) compared with those with positive calcium retention (mean, 101.5 mg per day; P = .01). However, there were no between-group differences for calcium intake, percent calcium absorption or true calcium absorbed.
Apart from one outlier, 24-hour urine calcium was associated with HbA1c, according to researchers.
They also found that fractional calcium absorption was inversely correlated with calcium intake in participants not meeting the recommended daily allowance (Spearman rank correlation, 0.65; P = .04).
According to the researchers, 40% of late pubertal participants with type 1 diabetes had negative estimated calcium retention.
“All participants were under 18 years and within 3 years of menarche, and therefore would be expected to be accruing bone mineral and retaining calcium,” they wrote. “In the context of previous studies that identified bone mineral deficits in [type 1 diabetes], this result suggests insufficient calcium availability for bone mineralization as a possible mechanism underlying the finding of low BMD in patients with [type 1 diabetes].” – by Regina Schaffer
Disclosures: The authors report no relevant financial disclosures.