Doria K. Thiele, Jody Ralph, Maher El-Masri, Cindy M. Anderson

To identify the combined effect of prenatal and postnatal vitamin D3 supplementation on the vitamin D status of pregnant and lactating women and their exclusively breastfed infants. Double-blind, randomized controlled trial. Upper Midwestern U.S., hospital-based obstetric practice. Pregnant women (N = 13) planning to exclusively breastfeed were randomized at 24 to 28 weeks gestation to receive vitamin D3 at a dosage of 400 IU (control group, n = 6) or 3,800 IU (intervention group, n = 7) daily through 4 to 6 weeks postpartum. Vitamin D status was determined at enrollment and in mother-infant dyads at 24 to 72 hours after birth and 4 to 6 weeks postpartum. Serum 25-hydroxyvitamin D levels were measured to determine the effect of vitamin D3 supplementation on the vitamin D status of mothers and infants. Analysis of covariance was used to compare differences in 25-hydroxyvitamin D levels between the control and intervention groups. The mothers' vitamin D levels were significantly higher in the intervention group than in the control group at birth (p = .044) and at 4 to 6 weeks postpartum (p = .002). Infants in the intervention group had significantly higher vitamin D levels at birth (p = .021) and nonsignificant, clinically relevant increases at 4 to 6 weeks of age (p = .256). No differences were found between maternal groups in serum calcium or parathyroid hormone levels. Prenatal to postpartum vitamin D3 supplementation is an effective intervention to increase a mother's vitamin D status and to promote optimal vitamin D status in newborns and exclusively breastfed infants.