Minimal Vitamin D and High Calcium and Phosphorus Needs of Preterm Infants Receiving Parenteral Nutrition

Abstract

Preterm infants (birth weight, 1,089 ± 91 g; gestational age, 28.9 ± 0.7 weeks; mean ± SEM) with mixed medical and surgical indications for parenteral nutrition (PN) were observed to determine the adequacy of infusates with fixed, low‐dose vitamin D (25 IU/dl) and two combinations of calcium and phosphorus. The duration of low‐dose vitamin D PN ranged from 5 to 52 days, with a median of 27 days. Twelve infants were randomly assigned to low (standard) Ca and P doses (5 mM each; 20 mg/dl of Ca and 15.5 mg/dl of P) and 13 high Ca and P doses (15 mM each; 60 mg/dl of Ca and 46.5 mg/dl of P). The maximum daily vitamin D intake was similar for both groups (31 ± 1.3 versus 33 ± 1.2 IU/kg). Vitamin D status in either group, as indicated by serum 25‐hydroxyvitamin D (25‐OHD) concentrations, was normal. There was no significant difference in observed changes of serial measurements of serum calcium, magnesium, phosphorus, alkaline phosphatase, creatinine (Cr), 25‐OHD, and vitamin D‐binding protein concentrations or urinary Ca:Cr and Mg:Cr ratios. In the low‐dose Ca and P group, the serum P level was consistently <4 mg/dl in five infants, serum 1,25‐dihydroxyvitamin D concentrations were higher, and tubular reabsorption of phosphorus was consistently <95% and significantly higher than in the high‐dose Ca and P groups. Severe bone demineralization apparent on X‐ray occurred in two infants, with a fractured distal left ulna in one of the two infants. Abdominal ultrasonograms showed gallbladder “sludge” in six infants (four in the low‐dose and two in the high dose Ca, P group) that resolved with enteral feeding. We conclude that for preterm infants receiving PN, the vitamin D requirement is minimal. A high Ca‐ and P‐level (15 mM each) infusate may be more appropriate than low Ca and P levels (5 mM each) to maintain Ca and P homeostasis.