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. 

  • Vitamin D undergoes sequential hydroxylation in the liver to 25-hydroxycholecalciferol (25-(OH)-D), also known as calcidiol, and in the kidney to the final product, 1,25-(OH)2-D, also known as calcitriol.  
  • Calcidiol represents the primary circulatory and storage form of vitamin D.  

Vitamin D deficiency and insufficiency are common, and pediatricians should have a low threshold for diagnosing and treating vitamin D deficiency.  

Most neonates 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 neonates have limited physical activity.
  • Preterm neonates excrete more phosphorus than term neonates.
  • Diuretics or steroids, often given to preterm neonates, cause low calcium levels. 

Osteopenia in preterm neonates 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 after birth for very preterm infants. 

Routinely evaluate bone mineral status for newborns and infants with birth weight <1,500 g but not those with birth weight >1,500 g.  

  • Biochemical testing should usually be started 4 to 5 weeks after birth. 

Treatment of Osteopenia

The fetus accrues ~80% of calcium, phosphorus, and magnesium present at term. For normal bone mineralization, preterm infants require higher intake of these minerals than term infants. 

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 neonates. 
  • Human milk fortifiers (for human milk–fed neonates) and special formulas with added minerals are available in the United States and many other countries for feeding preterm neonates. 
  • 10% to 20% of hospitalized infants with birth weight <1,000g have radiologically defined rickets.

Osteopenia in preterm neonates requires monitoring and testing.

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

In very low birth rate (VLBW) preterm neonates 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. 

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

  • Preterm newborns and infants, especially those born at <27 weeks’ gestation or with birth weight of <1,000 g with a history of multiple medical problems, are at high risk of rickets.
  • Routine evaluation of bone mineral status by using biochemical testing is indicted for newborns and infants with birth weight <1,500 g but not those with birth weight >1,500 g. Biochemical testing should usually be started 4 to 5 weeks after birth.
  • Serum alkaline phosphatase activity greater than 800 to 1,000 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 <4.0 mg/dL should be followed, and consideration should be given for phosphorus supplementation.
  • Routine management of preterm newborns and infants, especially those with birth weight <1,800 to 2,000 g, should include human milk fortified with minerals or formulas designed for preterm newborns and infants.
  • At the time of discharge from the hospital, VLBW newborns and infants will usually be provided higher intakes of minerals than are provided by human milk or formulas intended for term newborns and 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 newborns and infants reach a body weight >1,500 g and tolerate full enteral feeds, vitamin D intake should generally be approximately 400 IU/day, up to a maximum of 1,000 IU/day. 

The development of this resource was made possible with support from Abbott. The AAP maintains full independence in its editorial and strategic activities. Financial supporters have no influence over AAP content, policies, or leadership decisions.

Last Updated

02/12/2026

Source

American Academy of Pediatrics