High-Dose Vitamin D 3 Supplementation in a Cohort of Breastfeeding Mothers and Their Infants: A 6-Month Follow-Up Pilot Study

Objective: To examine the effect of high-dose maternal vitamin D₃ (vitD) supplementation on the nutritional vitD status of breastfeeding (BF) women and their infants compared with maternal and infant controls receiving 400 and 300 IU vitD/day, respectively.

Design: Fully lactating women (n = 19) were enrolled at 1–month postpartum into a randomized- control pilot trial. Each mother received one of two treatments for a 6–month study period: 0 or 6000 IU vitD₃ plus a prenatal vitamin containing 400 IU vitD₃. The infants of mothers assigned to the control group received 300 IU vitD₃/day; those infants of mothers in the high-dose group received 0 IU (placebo). Maternal serum and milk vitD and 25(OH)D were measured at baseline then monthly; infant serum vitD and 25(OH)D were measured at baseline, and months 4 and 7. Urinary calcium/creatinine ratios were measured monthly in both mothers and infants. Dietary and BF history and outdoor activity questionnaires were completed at each visit. Changes in skin pigmentation were measured by spectrophotometry. Data were analyzed using chi-square, t-test, and analysis of variance (ANOVA) on an intent-to-treat basis.

Results: High-dose (6400 IU/day) vitD₃ safely and significantly increased maternal circulating 25(OH)D and vitD from baseline compared to controls (p < 0.0028 and 0.0043, respectively). Mean milk antirachitic activity of mothers receiving 400 IU vitD/day decreased to a nadir of 45.6 at visit four and varied little during the study period (45.6–78.6 IU/L), whereas the mean activity in the 6400 IU/day group increased from 82 to 873 IU/L (p < 0.0003). There were no differences in circulating 25(OH)D levels of infants supplemented with oral vitD versus infants whose only source of vitD was breast milk

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Conclusion: With limited sun exposure, an intake of 400 IU/day vitamin D₃ did not sustain circulating maternal 25(OH)D levels, and thus, supplied only extremely limited amounts of vitamin D to the nursing infant via breast milk. Infant levels achieved exclusively through maternal supplementation were equivalent to levels in infants who received oral vitamin D supplementation. Thus, a maternal intake of 6400 IU/day vitamin D elevated circulating 25(OH)D in both mother and nursing infant.