Plasma concentrations of vitamin D metabolites in unsupplemented breast-fed infants.

Plasma concentrations of the vitamin D metabolites 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, 24,25-dihydroxyvitamin D and 25,26-dihydroxyvitamin D were determined in 12 solely breast-fed infants 4 days and 6 weeks after birth. They were not exposed to sunlight, but the mothers received an average of 600 IU vitamin D2 per day during the study period. The mothers' 25-hydroxyvitamin D levels did not change significantly (medians 42 and 58 nmol/l), but the median level dropped from 26 to 15 nmol/l in the infants (P less than 0.001). There was a close correlation between maternal and infant levels at 4 days (r = 0.95). The babies with the highest initial levels showed the most marked decrease by 6 weeks. The median concentrations of 24,25-dihydroxyvitamin D and 25,26-dihydroxyvitamin D decreased similarly from 1.7 to 0.8 and 0.63 to 0.35 nmol/l respectively, (P less than 0.001). The 1,25-dihydroxyvitamin D levels were within normal limits as were plasma calcium, phosphorus, and alkaline phosphatase. The data suggest that fetal stores of vitamin D may be rapidly depleted, and that breast milk may be inadequate as the only source of vitamin D, even for breast-fed infants of vitamin D-supplemented mothers.