Evaluation of the total fetomaternal vitamin D relationships at term: evidence for racial differences.

The present study assessed the total fetomaternal vitamin D relationship at term in 12 white and 10 black mothers and their infants. Antirachitic sterols were extracted from plasma, chromatographed, and finally quantitated using competitive protein binding assays. Compounds quantitated included vitamins D2 and D3, 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D2, 24,25-dihydroxyvitamin D3, 25,26-dihydroxyvitamin D3, 1,25-dihydroxyvitamin D2, and 1,25-dihydroxyvitamin D3. There was a strong correlation between maternal and neonatal plasma concentrations of all antirachitic sterols measured with the exception of vitamins D2 and D3. Vitamins D2 and D3, although detectable in maternal plasma, were undetectable in neonatal plasma. Racial comparisons demonstrated that vitamin D3, 25-hydroxyvitamin D3, 24,25-hydroxyvitamin D3, and 25,26-(OH)2-D3 were significantly (P less than 0.05) higher in white than in black mothers. Total 25-hydroxyvitamin D and 24,25-hydroxyvitamin D were also significantly (P less than 0.05) higher in white than in black mothers. A similar pattern was found in black and white infants except for 25,26-(OH)2-D3. Black mothers and their infants had significantly (P less than 0.05) higher 1,25-hydroxyvitamin D3 compared to the white subjects, although total 1,25-hydroxyvitamin D was not different between races. No significant racial (P greater than 0.05) differences were found for any of the vitamin D2 compounds. The results support the concept that fetomaternal vitamin D status are intimately related. Further, they strongly suggest that fetal metabolism begins with 25-hydroxyvitamin D rather than vitamin D. Finally, racial factors appear to influence the overall vitamin D status of both mother and fetus, and may influence antirachitic sterol metabolism.