Calcium, Phosphorous, and Vitamin D

 Background
 Assessment
 Interventions

Background

Although advances in early nutritional care of VLBW infants have reduced incidence of rickets of prematurity and osteopenia considerably, high risk infants may continue to have decreased bone mineral content which persists beyond 1 year of age (Abrams, 1989).

Risk factors for osteopenia include:

• Long term diuretic exposure
• Long term corticosteroid therapy
• Long term exposure to total parenteral nutrition
• Feedings of standard formula, soy formula or unfortified human milk before achieving weights of 2000 g

Assessment

For very high risk infants it may be appropriate to routinely monitor bone status. Assessment may include:

• Biochemical: Measure alkaline phosphatase, calcium, and phosphorus every two months. In the absence of other disease conditions, alkaline phosphatase provides an indirect indicator of bone cell activity. Higher alkaline phosphatase in conjunction with lower calcium and phosphorus indices may indicate a need for further supplementation. On the other hand, alkaline phosphatase levels might also rise during periods of rapid growth. In the absence of abnormal calcium and phosphorus indices, a rise in alkaline phosphatase should be followed closely, but may not indicate a need for nutritional intervention.
• Bone Mineral Content: As dual-energy x-ray absorptiometry (DEXA) and other methods of determining bone mineral content become more available to clinicians, it is reasonable to suggest its use in high risk infants. Sequential tests may be most appropriate for an individual infant, as normative values are not based on VLBW infants.

Interventions

Vitamin D: The AAP recommends that preterm infants receive 200-400 IU vitamin D in the hospital and after discharge. (Abrams, 2013)

Calcium and Phosphorus: Some studies suggest that infants fed nutrient enriched formulas with additional calcium and phosphorus show improvements in growth and mineral status (Lucas, 1992; Wheeler, 1996; Chan, 1994). For infants with osteopenia a modified transition from premature formula to standard formula or use of a commercial preterm post-discharge formula after discharge may be options. Use of premature formula after discharge should be carefully monitored to avoid excess intake of fat soluble vitamins (Vitamin A and Vitamin D). Infants at higher risk for rickets include those: born at <27 weeks gestation, with birth weight <1000 g, who received long-term parenteral nutrition, who had severe BPD with use of loop diuretics and fluid restriction, with long-term steroid use, with a history of nec, or who were unable to tolerate formulas or fortifiers with high mineral content (Abrams, 2013).

Hall found that at eight-weeks post discharge, a group of breastfed infants with birth weights less than 1800 g had lower incidence of hypophosphatemia and a trend toward lower alkaline phosphatase levels when breastmilk was supplemented. The regimen used in this study was 100 mg/kg/d of 10% calcium lactate and 50 mg/kg/d of phosphorus in the form of monobasic and dibasic salts. Both supplemented and non-supplemented groups received 400 IU vitamin D per day. This study suggests that some breastfed infants may benefit from increased calcium, phosphorus and vitamin D after discharge. Other investigators, however, have demonstrated spontaneous improvement in bone mineral content of breast fed babies after discharge (Congdon, Bishop). For infants with significant osteopenia, modified transition from fortified breastmilk or supplementation with premature formula may be options. Use of calcium and phosphorus supplements may not be tolerated and may result in abnormal calcium/phosphorus balance and requires close monitoring.

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