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.