Vitamin D, bone density, and nephrocalcinosis in preterm infants: a prospective study

Background: Vitamin D (VitD) supplementation is recommended by the American Academy of Pediatrics (AAP) for preterm infants to improve bone density. Complications of VitD supplementation include hypercalciuria and nephrocalcinosis (NC). NC has been reported in 7–64% infants < 32 weeks gestational age (GA) or < 1500 g birth weight (BW). The relationships between VitD supplementation, serum 25-hydroxy VitD levels, bone density, hypercalciuria and development of NC in preterm infants are not well established. Methods: Prospective, observational cohort study of 56 infants with GA ≤ 32 weeks or BW ≤ 1800 g. Demographics, dietary intakes, serum 25-hydroxy VitD levels and weekly urinalyses were collected until 40 weeks corrected GA or discharge. Bone mineral density (BMD) and content (BMC) were assessed using dual-energy X-ray absorptiometry (DEXA) scan. NC was identified by kidney ultrasound. Results: 56 infants received on average 447 IU/day of VitD with average serum 25-hydoxy VitD level 39.6 ng/mL. DEXA scan showed average BMD 0.13 g/cm² and BMC 35.8 g. 23/56 (41%) infants were diagnosed with NC. Infants with NC had lower GA (p < 0.01) and BW (p < 0.01) and increased presence of calcium oxalate crystals (78% vs. 36%) (p = 0.002). There were no differences in VitD intake, urine calcium/creatinine ratios or BMD and BMC in infants with versus without NC. Conclusions: VitD supplementation per AAP guidelines resulted in acceptable serum 25-hydroxyVitD levels, but no improvement in BMD or BMC compared to previously reported values. However, infants receiving recommended amounts born at earlier GA and lower BW are at increased risk of NC. VitD supplementation and serum levels should be closely monitored in this high-risk population. Graphical abstract: A higher resolution version of the Graphical abstract is available as Supplementary information. [Figure not available: see fulltext.].