Vitamin D activity of breast milk in women randomly assigned to vitamin D3 supplementation during pregnancy

Background: Human milk is typically low in vitamin D activity (VDA). Whether the vitamin D content of breast milk at birth can be increased by supplementing the mother during pregnancy has not been reported to the best of our knowledge. Objective: We examined the effect of vitamin D supplementation during pregnancy on breast-milk VDA in the first 2 mo of lactation. Design: Breast-milk samples were obtained from women who were enrolled in a randomized, double-blinded, placebo-controlled trial. of vitamin D supplementation during pregnancy. Pregnant women were enrolled at 27 wk of gestation and randomly assigned to the following 3 groups: a placebo group, a group who received one dosage of daily oral vitamin D-3 (1000 IU), or a group who received 2 dosages of daily oral vitamin D-3 (2000 IU). Serum 25-hydroxy-vitamin D [25(OH)D] was measured at enrollment, at 36 wk of gestation, and in cord blood at birth. Study participants who were breastfeeding were invited to provide breast-milk samples for VDA measurement [concentration of vitamin D-2, vitamin D-3, 25(OH)D-2, and 25(OH)D-3] at 2 wk and 2 mo postpartum. A linear mixed model was used to compare breast-milk VDA between the 3 study groups. Results: A total of 75 women provided breast-milk samples (44 women provided breast-milk samples at both 2 wk and 2 mo postpartum). The mean (95% CI) VDA at age 2 wk was 52 IU/L (12, 217 IU/L) in the placebo group, 51 IU/L (17, 151 IU/L) in the 1000-IU group, and 74 IU/L (25, 221 IU/L) in the 2000-IU group; and at age 2 mo, the mean (95% CI) VDA was 45 IU/L (16, 124 IU/L), 43 IU/L (18, 103 IU/L), and 58 IU/L (15, 224 IU/L), respectively. There was no significant interaction in VDA between the sample-collection time and treatment (P = 0.61), but there was a difference between lower- and higher-dosage treatment groups (P = 0.04). Conclusion: Maternal vitamin D supplementation during pregnancy of 2000 IU/d (compared with 1000 IU/d and with a placebo) results in a higher VDA of breast milk >= 2 mo postpartum. This trial was registered at the Australian New Zealand Clinical Trials Registry as ACTRN12610000483055.