Mineral balance studies in very low birth weight infants fed human milk

Mineral homeostasis often is disrupted in the very low birth weight (VLBW) infant fed either human milk or commercial formula that contains insufficient quantities of available calcium (Ca) and phosphorus (P). Alterations in mineral homeostasis include abnormal patterns of serum (Ca and P concentrations and alkaline phosphatase activity) and urine (Ca and P) biochemical markers, low net Ca and P retentions in comparison with intrauterine estimates of mineral accretion, and decreased bone mineral content. A two-phase study was conducted in our laboratory to test for these alterations in mineral homeostasis. In phase 1, VLBW infants fed a preparation of fortified human milk (either human milk-derived fortifier I or II or cow milk-derived fortifier) or cow milk-based formula specially designed for VLBW infants were evaluated during their hospitalization. In phase 2, after hospitalization, these infants were evaluated during the first 6 months of life when fed either their mother's milk or routine formula exclusively. The bioavailability of Ca and P from the tested preparations varied widely. Although the fortification of human milk resulted in both an improved biochemical pattern and net retention of Ca and P, optimal intrauterine mineral accretion was not achieved in any group tested. Longitudinal assessments of bone mineralization, by single photon absorptiometry, demonstrated that human milk-fed former VLBW infants had reduced bone mineral content. These investigations suggest that former VLBW infants fed human milk exclusively may be at risk for Ca and P deficiencies.