Maternal concentrations of vitamin D metabolites in response to high-dose oral vitamin D during first trimester pregnancy: a randomized controlled trial.

Vitamin D deficiency has become a common problem globally. The present study aimed to evaluate the effects of different vitamin D3 regimens on maternal concentrations of vitamin D metabolites during pregnancy. Subjects were ≤ 14 weeks gestation pregnant women with 25(OH)D serum level < 30 ng/mL]. Two intervention groups were randomly assigned: 5,000 IU of vitamin D3 daily or 50,000 IU weekly of vitamin D3. Maternal blood samples were collected before and after four weeks of intervention to assess changes in serum concentrations of 25-hydroxyvitamin D (25(OH)D), 1,25-dihydroxyvitamin D (1,25(OH)₂D), vitamin D binding protein (VDBP), and 24,25-dihydroxyvitamin D (24,25(OH)2D). Sixty subjects were randomized into two groups, and eight subjects were dropped out. There were no differences in the baseline demographics or baseline levels of any of the vitamin D metabolites between the two groups. In the 50,000 group, the 25(OH)D levels increased from 15.3 ± 4.7 ng/mL to 26.9 ± 6.1 ng/mL (p < 0.001) and 34.6% of the subjects achieved vitamin D sufficiency. While in the 5,000 group, the 25(OH)D levels increased from 14.5 ± 4.3 ng/mL to 27.9 ± 9.3 ng/mL (p < 0.001) and 23.1% of the subjects achieved vitamin D sufficiency. Both groups showed an increasing trend in the total levels of 25(OH)D, 1,25(OH)2D, VDBP, and 24,25(OH)2D. However, the increment of all vitamin D metabolites were not significantly different between two groups. Vitamin D3 50,000 IU weekly is equally effective and safe as 5,000 IU daily in increasing vitamin D levels in pregnant women with vitamin D deficient or insufficient. This randomized controlled trial was retrospectively registered at ClinicalTrials.gov (NCT06054919) on 22nd September 2023.