Serial analyses of serum vitamin D-binding protein in preterm infants from birth to postconceptual maturity.

Serial measurements of vitamin D-binding protein (DBP) were made in 28 infants of 29.7 +/- 2 weeks gestation and 1162 +/- 344 g birthweight. Mean (+/- SD) values (micrograms per ml) were: cord, 375 +/- 97; 1 week, 396 +/- 82; 3 weeks, 382 +/- 67; 6 weeks, 393 +/- 78; 9 weeks, 372 +/- 120; and 12 weeks, 490 +/- 130. At 12 weeks of age (40-42 weeks postconceptual age), DBP, 25-hydroxyvitamin D (25OHD), calcium, phosphorus, copper, and albumin were all significantly increased (by paired t test). At this point, but not earlier, DBP was correlated with 25OHD (r = 0.69; P less than 0.01) and phosphorus (r = 0.49; P less than 0.05), and 25OHD was correlated with phosphorus (r = 0.48; P less than 0.05) and calcium (r = 0.44; P less than 0.05). This may represent a concomitant maturation of the liver's protein synthetic abilities and the absorption and/or 25-hydroxylation in the liver of the parent vitamin D.