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Vitamin D metabolism in preterm infants: effect of a calcium load
E E Delvin1, B L Salle, F H Glorieux
1Shriners Hospital, Department of Surgery, Montreal, Canada.
Insights
Hypocalcemia in premature infants is common. A 24-hour calcium infusion normalized calcium levels, decreased parathyroid hormone, and increased vitamin D, showing an appropriate response to increased calcium supply.
Area of Science:
- Neonatal Medicine
- Pediatric Endocrinology
- Biochemistry
Background:
- Hypocalcemia is frequent in premature neonates within the first week of life.
- Premature infants were fed phosphate-enriched human milk and given vitamin D3.
- Eight premature neonates with hypocalcemia in the first 4 days of life were studied.
Purpose of the Study:
- To evaluate the effect of a 24-hour pharmacologic calcium infusion on serum levels of calcium, inorganic phosphate, magnesium, 25-hydroxycalciferol (25-OHD), 1 alpha,25-dihydroxycalciferol [1,25(OH)2D], and immunoreactive parathyroid hormone (iPTH).
Main Methods:
- Administered a 24-hour pharmacologic calcium infusion to eight premature neonates with hypocalcemia.
- Monitored serum levels of calcium, inorganic phosphate, magnesium, 25-OHD, 1,25(OH)2D, and iPTH before and after the infusion.
Main Results:
- Circulating iPTH and inorganic phosphate levels dropped significantly after calcium infusion (p < 0.025 and p < 0.005, respectively).
- Serum calcium and 25-OHD levels increased significantly (p < 0.005).
- Serum magnesium and 1,25(OH)2D levels remained unchanged.
Conclusions:
- A 24-hour increased calcium supply induces an appropriate response in iPTH secretion in premature neonates.
- Variability in 1,25(OH)2D levels may reflect individual differences in half-life or feedback mechanisms.
- This study provides insights into calcium homeostasis management in premature infants.
Abstract:
Decrease in serum calcium level leading to hypocalcemia during the first week of life is a frequent finding in premature neonates. Eight premature neonates presenting with such an episode of hypocalcemia in the course of their first 4 days of life were studied. They were fed with a phosphate-enriched human milk and given vitamin D3 (2,100 IU/day per os). We have evaluated the effect of a 24-hour pharmacologic calcium infusion on the circulating levels of calcium, inorganic phosphate, magnesium, 25-hydroxycalciferol (25-OHD), 1 alpha,25-dihydroxycalciferol [1,25(OH)2D] and immunoreactive parathyroid hormone (iPTH). After the infusion, circulating iPTH and Pi levels dropped significantly (p less than 0.025 and p less than 0.005 respectively) whereas serum Ca and 25-OHD (p less than 0.005) increased. Mg and 1,25(OH)2D serum levels remained unchanged. Our data show that an increased calcium supply sustained for 24 h induces an appropriate response in iPTH secretion. Effects on circulating levels of 1,25(OH)2D were variable and probably reflected individual differences in half life of 1,25(OH)2D or in set points in the feedback mechanisms involved in the control of 1,25(OH)2D synthesis.