Vitamin D status and response to supplementation in very preterm infants: A prospective cohort study

Abstract Background Very preterm infants are at high risk of vitamin D deficiency (VDD), which contributes to metabolic bone disease (MBD) and other morbidities. Despite guidelines, optimal dosing remains uncertain. We determined VDD incidence and evaluated 25-hydroxyvitamin D 25(OH)D responses to varying vitamin D intakes during the first 8 weeks of life. Methods This prospective cohort enrolled infants born at 700 IU/kg/day. Serum 25(OH)D was measured at birth, 4, and 8 weeks. Biochemical markers and MBD screening were performed. VDD was defined as 25(OH)D 100 ng/mL. Results Among 126 infants (gestational age 30 27, 31 weeks; birth weight 1230 950, 1570 g), 94.3% had VDD at birth. At 4 weeks, VDD persisted in 17.8% receiving <400 IU/kg/day and 6.5% receiving 400–700 IU/kg/day; vitamin D excess (VDE) occurred in 3.3% and 3.2%, respectively. At 8 weeks, normal 25(OH)D was achieved in 90.1% receiving <400 IU/kg/day and 77.4% receiving 400–700 IU/kg/day, while VDE increased to 8.6% and 22.6%, respectively. Biochemical markers remained normal; only one infant developed MBD. Conclusions VDD is highly prevalent at birth in very preterm infants. Daily intake <400 IU/kg generally normalizes vitamin D status by 8 weeks while minimizing risk of excessive vitamin D. Higher doses may provide no additional benefit and increase risk of exceeding 25(OH)D levels. Clinical trial registration Thai Clinical Trials Registry. Registration number TCTR20230725007. Web link: http://www.thaiclinicaltrials.org/show/TCTR20230725007 .