Role of Calcium-Phosphate Ratio of Milk Formulae on Calcium Balance in Low Birth Weight Infants during the First Three Days of Life

Abstract

Summary: Twenty-six low birthweight infants with no differences in the neonatal status were allocated into three groups. Group A (10 infants), Group B (8 infants), and C (8 infants) received formulae with 2.4, 1.6, and 4.1 Calcium/Phosphate (Ca/Pi) ratio respectively. Formula C was supplemented with calcium lactate 800 mg/ kg/day, which yielded 12.7 ± 0.4 mg of Ca and 0.04 ± 0.002 mg of Mg per each 100 mg of salt (mean ± S.D.). The osmolality of the C formula before its administration was 361 ± 52 mOsm/kg. Balances (mean ± S.D.) from the first feeding up to a period of 3 days were obtained. The intestinal product before any feeding contained: Ca, 1.3 ± 0.6 mg/kg; Mg, 2.9 ± 1.5 mg/kg, and Pi, 1.5 ± 2.3 mg/kg. Calcium intake (mg/kg/day) was 89.7 ± 13.8 for formula A, 71.1 ± 12.5 for formula B, and 156.8 ± 19.8 for formula C. Their net retention (mg/kg/day) was 50.8 ± 15.9, 39.3 ± 12.8 (P < 0.05), and 105.2 ± 21.9 (p < 0.001) respectively.

Net retention of Pi was comparable in the three groups (A, B and C) ranging 24.7–25.7 mg/kg/day. Small variations in intake are finely compensated by parallel urinary excretion (range 6.3–12.8 mg/kg/day).

Magnesium absorption did not show differences among the three formulae. The evolution of plasmatic values for magnesium was fairly normal in the three groups. Phosphatemia was significantly (P < 0.01) lower in group A (lowest Pi containing formula) on the 3rd day. Patients on formula B (smaller Ca content) showed a mean blood calcium of 7.9 mg/dl, which was significantly lower than in the other groups. In two instances, blood calcium was lower than 6.9 mg/dl (Z = 6.32; P < 0.05). Net retention of calcium correlates positively with Ca/Pi ratio (r = 0.82) and with absolute Ca intake (r = 0.84). Calcium lactate supplementation did not modify acid base equilibrium, lactatemia nor digestive tolerance.

Speculation: To prevent demineralization in the early postnatal period of preterm babies, the net retention of calcium could be improved more effectively by adding a calcium supplement to the formula rather than by decreasing its Pi content, even though both procedures lead to a comparable Ca/Pi quotient.

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