Plasma levels of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in maternal, cord and neonatal blood.

A high-performance liquid chromatographic method for simultaneous assay of 25-hydroxyvitamin D2 (25-OH-D2) and 25-hydroxyvitamin D3 (25-OH-D3) proposed in a previous paper (1) was applied to determine the plasma levels of the metabolites in perinatal and postnatal periods. The plasma samples of maternal, cord and neonatal blood were collected in summer and winter seasons. 25-Hydroxyvitamin D3 was detected in all the samples. The plasma levels of the metabolite in mothers, cords and newborn infants (at life within 24 hr) in summer were 33.9 +/- 12.5, 18.9 +/- 8.4 and 16.6 +/- 6.4 (mean +/- S.D.) ng/ml, respectively, while those in winter were 15.8 +/- 6.6, 8.8 +/- 3.4 and 7.7 +/- 3.2 ng/ml, respectively. The data in summer were significantly higher than the respective data in winter and there were high significant correlations between the mothers and cords and between mothers and newborns. In both seasons, the plasma levels of mothers were about two times higher than the respective data of cords and newborns which were nearly identical with one another. The similar tendency was always observed in the individual data of mothers-cords-newborns pair samples. In this study, many plasma samples from mothers, cords and newborns were examined, but 25-OH-D2 was detected in only few samples (6/41 for mothers, 3/36 for cords and 2/34 for newborns). However, the metabolite began to appear in all the samples during nursing with vitamin D2-fortified dry milk to show 4.6 +/- 1.3 and 4.8 +/- 1.2 ng/ml in the summer and winter samples of neonates at life of 5-6 days, respectively. When the variation of plasma 25-OH-D2 and 25-OH-D3 levels was examined in postnatal periods until one month, the levels of exogenous 25-OH-D2 was increased while those of endogenous 25-OH-D3 was decreased. The sum of vitamin D2 intake from fortified dry milk was highly significantly correlated with the plasma levels of 25-OH-D2, which indicates that daily uptake of exogenous vitamin D2 is very important in nutrition during postnatal periods of bottle-fed infants.