The aim of this study was to investigate the correlation between the retention of calcium (Ca) and phosphorus (P) and weight gain and intake of Ca and P when using the concept of individualized Ca and P supplementation in extremely low birthweight infants. Three-day Ca and P balances were performed in 20 infants with a mean gestational age of 26.6wk (between 24.1 and 28.7 wk) and a birthweight of 744 g (450-990), when the infant was able to tolerate at least 100 ml/kg/d of milk. The daily supplementation with Ca and P was individually adjusted to achieve a simultaneous excretion of > or = 1.2 mmol/L Ca and > or = 0.4 mmol/L P in the urine. In 16 of the 20 infants, the urinary concentrations of both Ca and P exceeded the lower limits. The retention of Ca (mean 3.8 mmol/kg/d, minimum 0.9; maximum 8.1; 57% of intake, 34-80) and P (2.4,1.1-4.2; 76%, 52-96) was significantly correlated with both the daily weight gain (16 g, 3-28; Ca r2 = 0.22, p = 0.02; P r2 = 0.21, p = 0.03) and the intake of Ca (6.5 mmol/kg/d, 2.4-10.2; r2 = 0.67, p < 0.001) and P (3.1, 1.9-5.3; r2 = 0.85, p < 0.0001). The molar ratio of the Ca and P intake was 2.2 (1.3-4.0).
Conclusion: It was found that Ca and P retention was a function of growth and intake.