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.