Mineral homeostasis during lactation- relationship to serum 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D, parathyroid hormone and calcitonin.

During lactation maternal losses of calcium and phosphorus through human milk average 220 to 340 and 110 to 170 mg/day, respectively. The present study reports maternal serum concentrations of vitamin D metabolites, parathyroid hormone, calcitonin, calcium, magnesium, and phosphorus during the first 6 months of lactation. Serum calcium and magnesium concentrations increased during the first 6 months of lactation. Serum 1,25-(OH)2 vitamin D was increased at 6 months of lactation compared to values in nonpregnant nonlactating controls. During this same period, serum parathyroid hormone decreased slightly and serum calcitonin remained unchanged. Our data do not support the observation that lactation represents a state of physiological hyperparathyroidism. On the contrary, our results suggest that lactating women are able to adequately compensate for the losses of calcium and phosphorus during the early months of lactation, although increased serum 1,25-(OH)2 vitamin D concentrations may be necessary to maintain calcium homeostasis with lactation beyond 6 months.

Physiologic cholestasis: elevation of the primary serum bile acid concentrations in normal infants.

Immaturity of hepatic excretory function resulting in a period of "physiologic cholestasis" may occur during early life. Serum bile acids should accurately reflect maturation of the enterohepatic circulation; we therefore determined serum concentrations of the primary bile acids in normal infants to define age-related changes. There was a striking rise in serum cholylglycine and conjugates of chenodeoxycholate during the first few days of life over levels detected in cord sera; the values attained were significantly greater than maximal postprandial concentrations found in children over 1 yr of age (p less than 0.01). There was a gradual decline in bile acid concentration; however cholylglycine remained higher than the postprandial values of older children until 4 mo and chenodeoxycholate until 6 mo of age. In 12 infants a liquid feeding stimulated a greater maximal postprandial cholylglycine concentration and integrated area under the meal curve than that achieved in children (p less than 0.01). There was no difference in the postprandial response in chenodeoxycholate in these infants compared with the older subjects. We conclude that serum bile acids are elevated in normal infants and that the subsequent decline to levels of the child and adult demonstrates the evolving maturation of liver function during infancy.

Bone mineral content and serum 25-hydroxyvitamin D concentration in breast-fed infants with and without supplemental vitamin D.

Eighteen term, healthy, appropriate for gestational age, breast-fed infants were studied in a double-blind prospective study to determine whether or not supplemental vitamin D affected bone mineralization. All patients were from a single, private pediatric practice. Nine infants were randomly assigned to a vitamin D supplement of 400 IU/day and nine infants to a placebo. By 12 weeks of age, infants receiving placebo had a significant decrease in bone mineralization and in serum 25-hydroxyvitamin D concentrations compared to the vitamin D-supplemented group. It is not known whether or not the increased BMC at 12 weeks of age in vitamin D-supplemented breast-fed infants is of ultimate value. Supplemental vitamin D may be necessary for optimal bone mineralization in term breast-fed infants. A longer follow-up study and additional analyses are required to make conclusive statements.