Rickets in very low birthweight infants. Influence of supplementation with vitamin D, phosphorus and calcium.

The influence of extra phosphorus (P) and calcium (Ca) on the incidence of rickets was studied in 40 infants with a birthweight below 1.5 kg. All were fed breastmilk and all received vitamin D 1200 IU/day. Half of the infants were supplemented with P 20 mg/kg/day and Ca 30 mg/kg/day. Rickets, diagnosed with X-ray at 5 to 7 weeks of age, developed in 12 infants, 11 of whom weighed below 1.0 kg. In infants below 1.0 kg rickets was significantly more common in the group not receiving extra P and Ca. After diagnosis all were substituted and radiographic healing occurred in all. Serum Ca concentrations were normal in both groups whereas serum P was significantly lower in non-supplemented patients. Serum alkaline phosphatases (ALP) were normal in all patients at the time of diagnosis demonstrating the risk of using ALP as a diagnostic test for rickets in very low birthweight.