Time-course analysis of 3-epi-25-hydroxyvitamin D3 shows markedly elevated levels in early life, particularly from vitamin D supplementation in preterm infants

Background: An epimeric form of 25-hydroxyvitamin D-3 (25(OH)D-3) has recently been detected in clinical samples, with relatively high levels in infants. Little is known on 3-epi-25(OH)D-3 formation and physiological function. Our objective was to study dynamics of 3-epi-25(OH)D-3 formation during infancy. Methods: 25(OH)D-3 an 3-epi-25(OH)D-3 levels were measured by liquid chromatography-tandem mass spectrometry in 22 preterm (aged 34-37 wk), 15 early preterm (aged <34 wk), and 118 term infants up to 2 y of age. All infants were prescribed vitamin D 400 IU/day after the first week of life. Results: At birth, 3-epi-25(OH) D-3 levels were 3 (1-7) nmol/l, <10% of total 25(OH)D-3. From the second week to 3 mo of age, both 25(OH)D-3 anD(3)-epi-25(OH)D-3 increased, with highest 3-epi-25(OH)D-3 contribution in early preterm infants (up to 55% of total 25(OH)D-3 vs. 36% in term infants, P < 0.0001). After 3 mo of age, 3-epi-25(OH)D-3 normalized to <10% in all infants. Conclusions: At birth, all infants showed low contribution of 3-epi-25(OH) D3, increasing the week after starting vitamin D supplementation, until 3 mo of age. Highest levels of 3-epi25(OH)D-3 were found in early preterm infants, supporting the hypothesis that hepatic immaturity plays a role in 3-epi-25(OH) D-3 formation.