The long term objective of this proposal is to develop a more comprehensive understanding of neonatal vitamin D utilization. Our more immediate objective, however, is to define the antirachitic sterol requirements of preterm and term infants by studying vitamin D and its metabolites in relation to skeletal mineralization during various antirachitic sterol dietary regimes. Specifically, we propose to: 1) determine separately and individually the levels of vitamin D2 and D3, and their metabolites present in mothers plasma and milk and correlate these levels with the level of metabolites found in the blood of the nursing infant. This separation and individual quantitation of the vitamin D2 and D3 forms provides a powerful tool in assessing antirachitic sterol interactions between mother and the nursing infants; 2) determine the plasma levels of vitamin D2 and D3 and their metabolites in newborn infants of varying gestational age and birth weight while these infants are being fed differing vitamin D dietary regimens; 3) examine the effects of extended phototherapy on the antirachitic sterol content of human milk and how this phototherapy of the mother affects the mineral homeostasis of the nursing infant; 4) determine the vitamin D binding protein content of the mothers' plasma and milk in an effort to gain better insight into the transfer of vitamin D and its metabolites from blood to milk; 5) make serial measurements of other circulating components that reflect dynamic mineral metabolic status and calcium homeostatsis, including parathyroid hormone, calcitonin, total calcium, phosphorus, magnesium, alkaline phosphatase and ionized calcium; and 6) monitor neonatal bone mineralization vs. differing vitamin D dietary regimens by measuring the bone mineral content and bone width via direct photon absorptometry. This proposed study should provide insight into the obscure areas of neonatal vitamin D metabolism and dietary requirements. The data will provide information regarding the amount and type of vitamin D metabolites required by neonates at varying gestational ages. Finally, on a long-range basis, the data from this study could result in a redefinition of the vitamin D requirement for the low birth weight and/or premature neonate which would, in turn, facilitate the development of synthetic formulas for the developing newborn.
