Plasma 1.25-Dihydroxyvitamin D Concentrations in Preterm Infants

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Abstract
1,25-Dihydroxyvitamin D concentrations were measured in 10 preterm infants (mean gestational age 29 wk, range 26-32; mean birthweight 1226 g, range 980-1700). Total parenteral nutrition was begun after birth and partial enteral feeding was started at 1 wk of age. Total enteral feeding was achieved at a mean age of 26 days (range 16-47). The daily vitamin D3 intake was .apprx. 400 IU. No clinical, chemical or radiological signs of rickets were observed. The mean 1,25-dihydroxyvitamin D concentration .+-. SEM [standard error of the mean] was 103.2 .+-. 24.0 pmol/l at 1 wk (range 9.6-252.0), 141.6 .+-. 26.4 at 3 wk (range 31.2-324.0), 153.6 .+-. 21.6 at 6 wk (range 67.2-256.8), 165.6 .+-. 24.0 at 9 wk (range 74.4-307.2) and 153.6 .+-. 21.6 at 12 wk (range 76.8-268.8) postnatal age. The mean values at 6, 9 and 12 wk were significantly higher (P < 0.01, < 0.002 and < 0.005, respectively) than in adults (88.8 .+-. 7.2; n = 27). 1,25-Dihydroxyvitamin D concentrations were highly variable and did not correlate with 25-hydroxyvitamin D concentrations, plasma Ca and P concentrations and plasma alkaline phosphatase levels, nor with illness nor postnatal age. Preterm infants are apparently capable of producing high plasma levels of 1,25-dihydroxyvitamin D.