Bone accounts for 99% of the calcium, 80% of the phosphorus, and 60% of the magnesium in the body. The large reservoir of calcium in bone is important in maintaining calcium homeostasis, because a portion of bone calcium exchanges readily with the calcium of extracellular fluid.

Vitamin D facilitates transcellular calcium intestinal absorption. To achieve this effect, it must undergo sequential hydroxylation in the liver to calcidiol and in the kidney to the final product, 1,25-(OH)2-D also known as calcitriol. Calcidiol (25-hydroxyvitamin D [25-OH-D]) represents the primary circulatory and storage form of vitamin D.

Most infants born before 30 weeks’ gestation have some degree of osteopenia because

  • The third trimester of pregnancy is a time of rapid transfer of calcium and phosphorus to the fetus.
  • Fetal movement in the third trimester may stimulate bone development; most preterm infants have limited physical activity.
  • Premature infants excrete more phosphorus than term newborns
  • Diuretics or steroids, often given to premature infants, cause low calcium levels

Osteopenia of prematurity often has no symptoms.

  • When severe, bones are weak and brittle, and unknown fractures may be accompanied by swelling or decreased movement.
  • An increased risk for fracture often persists through the first year of life for very premature infants

Treatment of Osteopenia of Prematurity

Osteopenia in premature infants requires monitoring and testing:

  • Blood levels of calcium, phosphorus and alkaline phosphatase
  • Ultrasound
  • Radiography

Although minerals are well absorbed from human milk (60%–70%), the net retention of calcium and phosphorus are far below the rates in utero, therefore:

  • Supplementary calcium and phosphorus are needed to sustain optimal calcium balance in preterm infants.
  • Human milk fortifiers (for human milk-fed infants) and special formulas with added minerals are available in the United States and many other countries for feeding preterm infants.
  • Use of these products has led to net calcium retention comparable to that achieved in utero.

In VLBW preterm infants fed parenterally, the danger of calcium-phosphorus precipitation in the solution limits the amount that can be administered intravenously.

Although intrauterine rates of absorption are not achievable, intravenous solutions should be adequate to prevent severe osteopenia or rickets. In situations in which fluids are being restricted, this may be more difficult to achieve.

Infants who require oxygen or fluid restriction after hospital discharge, particularly benefit from providing a higher mineral intake than is available from human milk or from routine cow milk-based formulas.

AAP Recommendations for Calcium and Vitamin D of Enterally-Fed Preterm Infants

  • Preterm infants, especially those born at <27 weeks’ gestation or with birth weight <1000 g with a history of multiple medical problems, are at high-risk of rickets.
  • Routine evaluation of bone mineral status by using biochemical testing indicted for infants with birth weight <1500 g but not those with birth weight >1500 g. Biochemical testing should usually be started 4 to 5 weeks after birth.
  • Serum alkaline phosphatase activity >800 to 1000 IU/L or clinical evidence of fractures should lead to a radiographic evaluation for rickets and management focusing on maximizing calcium and phosphorus intake and minimizing factors leading to bone mineral loss.
  • A persistent serum phosphorus concentration less than approximately 4.0 mg/dL should be followed, and consideration should be given for phosphorus supplementation.
  • Routine management of preterm infants, especially those with birth weight <1800 to 2000 g, should include human milk fortified with minerals or formulas designed for preterm infants
  • At the time of discharge from the hospital, VLBW infants will usually be provided higher intakes of minerals than are provided by human milk or formulas intended for term infants with the use of transitional formulas. If exclusively breastfed, a follow-up serum alkaline phosphatase activity at 2 to 4 weeks after discharge from the hospital may be considered.
  • When infants reach a body weight >1500 g and tolerate full enteral feeds, vitamin D intake should generally be approximately 400 IU/day, up to a maximum of 1000 IU/day.

Vitamin D deficiency and insufficiency are common and pediatricians should have a low threshold for diagnosing and treating vitamin D deficiency. However, there is insufficient evidence to support universal screening for vitamin D deficiency among healthy children or children with dark skin or obesity.

Last Updated

05/31/2022

Source

American Academy of Pediatrics