Magnesium balance studies in premature and term infants

The knowledge of magnesium requirements of premature infants is still very limited, although it is essential for the optimal composition of suitable formulas.

The study concept was 1) to assess physiological magnesium balance data of healthy term infants and longitudinal results from formula-fed premature infants and 2) to deduce conclusions on the magnesium content of the formulas.

Premature infants (n = 14, birth weight < or = 1500 g, gestational age < or = 32 weeks) were studied in conventional balance trials with 1) a semi-elemental diet (A), 2) preterm infant formula (B), and 3) infant formula (C). In addition, healthy term formula-fed (n = 11, D) and breast-fed (n = 14, E) infants were investigated. Analysis was performed by flame atomic absorption spectroscopy.

The median magnesium intake ranged between 4.84 mg/kg x d-1 (breast-fed infants) and 16.33 mg/kg x d-1 (premature infants). The term breast-fed infants retained nearly as much magnesium as term formula-fed infants (3.37 vs. 3.97 mg/kg x d-1), due to a low percental fecal and urinary excretion. A higher magnesium retention was observed in the premature group: A: 7.97 mg/kg x d-1, B: 5.3 mg/kg x d-1, 3.) C: 5.54 mg/kg x d-1.

In view of the high percental magnesium retention in formula-fed premature infants, excessive supply should be avoided. The long-term effects of lower intakes have to be monitored.