VITAMIN D METABOLISM IN PRETERM INFANTS

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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.alpha.,25-dihydroxyvitamin D [1,25(OH)2D] were measured in 22 infants (31-35 wk of gestation) from birth up to 96 h of age. Compared to cord blood levels, serum Ca decreased significantly during the first 24 h of life (P < 0.005) and remained low until day 4. Serum immunoreactive parathyroid hormone (iPTH) levels increased from birth to 24 h 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 4 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. In preterm infants after 31 wk of gestation, absorption and activation of vitamin D is present as soon as 24 h after birth and early neonatal hypocalcemia is unlikely to be caused by an impairment of either PTH secretion or vitamin D activation.