Response to Prenatal and Postpartum Cholecalciferol Supplementation.

BACKGROUND Variability in the 25-hydroxyvitamin D (25(OH)D) response to prenatal and postpartum vitamin D supplementation is an important consideration for establishing vitamin D deficiency prevention regimens. OBJECTIVES We aimed to examine inter-individual variation in maternal and infant 25(OH)D following maternal vitamin D supplementation. METHODS In a randomized trial of maternal vitamin D supplementation (Maternal Vitamin D for Infant Growth Trial), healthy pregnant women (n = 1300) received a prenatal cholecalciferol (vitamin D3) dose of 0, 4200, 16800 or 28000 IU/week from 17-24 weeks' gestation followed by placebo to 6 months postpartum. A fifth group received 28000 IU cholecalciferol/week both prenatally and postpartum. In a subset of participants, associations of 25(OH)D with hypothesized explanatory factors were estimated among women at delivery (n = 655) and 6 months postpartum (n = 566), and among their infants at birth (n = 502) and 6 months of age (n = 215). Base models included initial 25(OH)D and supplemental vitamin D dose. Multivariable models were extended to include other individual characteristics and specimen-related factors. The model coefficient of determination (R2) was used to express the % of total variance explained. RESULTS Supplemental vitamin D intake and initial 25(OH)D accounted for the majority of variance in maternal 25(OH)D at delivery and postpartum (R2 = 70% and 79%, respectively). Additional characteristics, including BMI, contributed negligibly to remaining variance (<5% increase in R2). Variance in neonatal 25(OH)D was explained mostly by maternal delivery 25(OH)D and prenatal vitamin D intake (R2 = 82%). Variance in 25(OH)D in later infancy could only partly be explained by numerous biological, socio-demographic and laboratory-related characteristics, including feeding practices (R2 = 43%). CONCLUSIONS Pre-supplementation 25(OH)D and vitamin D supplemental dose are the major determinants of the response to maternal prenatal vitamin D intake. Vitamin D dosing regimens to prevent maternal and infant vitamin D deficiency should take into consideration the mean 25(OH)D concentration of the target population.