Elevated serum parathyroid hormone, calcitonin, and 1,25-dihydroxyvitamin D in lactating women nursing twins.

The roles of vitamin D, calcitonin, and parathyroid hormone in calcium metabolism during lactation may be more evident in women secreting very large amounts of milk for a number of months, as in mothers nursing twins. We report significant increases in serum concentrations of parathyroid hormone, calcitonin, and 1,25(OH)2 vitamin D in mothers nursing twins compared to mothers nursing single infants. Serum concentrations of calcium actually increased in both groups during lactation. Maternal intakes of calories, calcium, and phosphorus were significantly higher in mothers nursing twins. Thus, mothers nursing twins were able to compensate for higher calcium losses in breast milk by increased dietary intakes of calcium as well as increased serum concentrations of parathyroid hormone, calcitonin, and 1,25(OH)2 vitamin D.