The amount of enteral calcium, phosphorus, and magnesium intake required to match intrauterine accretion rates is high: calcium 185 to 200 mg/kg per day, phosphorus 100 to 113 mg/kg per day, and magnesium 5.3 to 6.1 mg/kg per day. VLBW infants with a less complicated clinical course may require lower intakes. The American Academy of Pediatrics recommends intakes of calcium of 185 to 210 mg/kg per day, phosphorus 123 to 140 mg/kg per day, and magnesium 8.5 to 10.0 mg/kg per day. However, magnesium intake at this level with such high calcium and phosphorus intake results in negative magnesium balance; therefore, a higher intake of magnesium approximately 20 mg/kg per day may be needed.
The recommendation for vitamin D, which is required for normal metabolism of calcium, phosphorus, and magnesium, has ranged from 200 to 2000 IU per day for the preterm infant. VLBW infants can maintain normal vitamin D status with 400 IU per day. Providing high-dose vitamin D supplementation does not decrease the incidence of osteopenia in VLBW infants.
Human milk has concentrations of calcium and phosphorus that are appropriate for full-term infants. These amounts are inadequate for the VLBW infant. Breast milk should be supplemented with additional calcium, phosphorus, and vitamin D, which can easily be done with a powdered human milk fortifier (Enfamil Human Milk Fortifier, Mead Johnson, Evansville, IN; Similac Human Milk Fortifier, Abbott Laboratories, Columbus, OH). Also recently available is a human milk fortifier (Prolact + H2MF, Prolacta, Bioscience, Monrovia, CA).