Randomized double-blind trial finds high-dose vitamin D does not alter glucose tolerance in pregnant women, indicating that supplementation primarily benefits neonatal vitamin D status.
Key Points
To evaluate whether high-dose compared to standard-dose vitamin D3 supplementation improves maternal glucose metabolism and prevents gestational diabetes.
Double-blind randomized controlled trial of pregnant women with plasma 25-hydroxyvitamin D <32 ng/mL before 20 weeks' gestation.
Participants received oral vitamin D3 at 5,000 IU daily (high-dose, n = 89) or 400 IU daily (low-dose, n = 90) until delivery.
Assessed primary maternal glucose levels via an oral glucose tolerance test at 26–28 weeks' gestation, alongside secondary neonatal and insulin resistance outcomes.
Maternal glucose levels on oral glucose tolerance tests did not differ between arms, with gestational diabetes occurring in 8% (7/89) of the high-dose group versus 13% (12/90) of the low-dose group (P = 0.25).
Neonatal cord blood 25-hydroxyvitamin D levels were significantly higher in the high-dose group compared to the low-dose group (46 ± 11 vs. 29 ± 12 ng/mL, P < 0.001), while neonatal deficiency was lower (10% vs. 24%, P = 0.06).