Maternal Versus Infant Vitamin D Supplementation During Lactation: A Randomized Controlled Trial.

OBJECTIVE: Compare effectiveness of maternal vitamin D3 supplementation with 6400 IU per day alone to maternal and infant supplementation with 400 IU per day.

METHODS: Exclusively lactating women living in Charleston, SC, or Rochester, NY, at 4 to 6 weeks postpartum were randomized to either 400, 2400, or 6400 IU vitamin D3/day for 6 months. Breastfeeding infants in 400 IU group received oral 400 IU vitamin D3/day; infants in 2400 and 6400 IU groups received 0 IU/day (placebo). Vitamin D deficiency was defined as 25-hydroxy-vitamin D (25(OH)D) <50 nmol/L. 2400 IU group ended in 2009 as greater infant deficiency occurred. Maternal serum vitamin D, 25(OH)D, calcium, and phosphorus concentrations and urinary calcium/creatinine ratios were measured at baseline then monthly, and infant blood parameters were measured at baseline and months 4 and 7.

RESULTS: Of the 334 mother-infant pairs in 400 IU and 6400 IU groups at enrollment, 216 (64.7%) were still breastfeeding at visit 1; 148 (44.3%) continued full breastfeeding to 4 months and 95 (28.4%) to 7 months. Vitamin D deficiency in breastfeeding infants was greatly affected by race. Compared with 400 IU vitamin D3 per day, 6400 IU/day safely and significantly increased maternal vitamin D and 25(OH)D from baseline (P < .0001). Compared with breastfeeding infant 25(OH)D in the 400 IU group receiving supplement, infants in the 6400 IU group whose mothers only received supplement did not differ.

CONCLUSIONS: Maternal vitamin D supplementation with 6400 IU/day safely supplies breast milk with adequate vitamin D to satisfy her nursing infant's requirement and offers an alternate strategy to direct infant supplementation.