RICKETS AND CALCIUM AND PHOSPHORUS REQUIR EMENTS IN VERY-LOW-BIRTH-WEIGHT INFANTS

Rickets can occur in up to 30% of infants with birth weight < 1500g, b ut the incidence may be as high as 70% in infants < 800g. In these inf ants the major cause of rickets/osteopenia appears to be calcium (Ca) and phosphate (P) deficiency. Additional risk factors are prolonged pa renteral nutrition and use of furosemide. Serum Ca is usually normal, while serum P is typically low, with elevated alkaline phosphatase. Th ere are no specific defects in hydroxylation steps for vitamin D in pr eterm infants. Mineral accretion in utero is high, reaching 150mg of C a/Kg of fetal weight, and 75mg of P/Kg, per day. Bone mineral content (BMC) increases linearly in the last trimester. Therefore preterm infa nts have reduced postnatal BMC, which can be increased by formulas wit h very high Ca and P content. On long term follow-up, BMC generally la gs behind that of normal term infants. Human milk fed preterm infants particularly have low P intake, low serum P concentrations and rickets and/or fractures at 6-8 weeks of age. P balances in human milk-fed pr eterm infants show very high intestinal absorption (about 90%) and ret ention (about 85%), with very low urinary excretion. Ca absorption in human milk-fed preterm infants is about 70%, with urine Ca excretion o f about 20%: retention rate is approximately 50% Provision of high min eral intake by parenteral and enteral routes appears to be appropriate to maintain or restore bone mass in preterm infants.