VITAMIN D METABOLISM IN PRETERM INFANTS

ABSTRACT. In order to evaluate after birth the changes in circulating vitamin D metabolite levels in preterm babies supplemented with vitamin D (2100 I. U./d), the serum concentration of 25-hydroxyvitamin D [25-OHD] and 1 α,25-dihydroxy vitamin D [1, 25(OH)₂D] were measured in 22 infants (31 to 35 weeks of gestation) from birth up to 96 hours of age. Compared to cord blood levels, serum calcium decreased significantly during the first 24 hours of life ( p <0.005) and remained low until day 4. Serum immunoreactive parathyroid hormone (iPTH) levels increased from birth to 24 hours and then plateaued. The 25-OHD levels at birth were 27.5±2.5 nmol/l and increased to 67.5±12.5 nmol/l ( p <0.005) during the four days of the study. During the same period, the 1, 25(OH)₂D serum levels increased steadily from 84<7 to 343<105 pmol/l ( p <0.005). At all times, there was a positive correlation between 25-OHD levels and those of 1, 25(OH)₂D. Our data demonstrate that in preterm infants after 31 weeks of gestation, absorption and activation of vitamin D is present as soon as 24 hours after birth and that early neonatal hypocalcemia is unlikely to be caused by an impairment of either PTH secretion or vitamin D activation.