Determinants of the maternal 25-hydroxyvitamin D response to vitamin D supplementation during pregnancy

Context: Current approaches to antenatal vitamin D supplementation do not account for inter-individual differences in 25-hydroxyvitamin D [25(OH)D] response. Objective: We assessed which maternal and environmental characteristics were associated with 25-hydroxyvitamin D [25(OH)D] following supplementation with cholecalciferol. Design: Within-randomisation-group analysis of participants in the MAVIDOS trial of vitamin Dsupplementation in pregnancy. Setting: Hospital antenatal clinics Participants: 829 pregnant women (422 placebo, 407 cholecalciferol). At 14 and 34 weeks’ gestation, maternal anthropometry, health and lifestyle were assessed and 25(OH)D measured. Compliance was determined using pill counts at 19 and 34 weeks. Interventions: 1000IU/day cholecalciferol or matched placebo from 14 weeks’ gestation until delivery. Main outcome measure: 25-(OH)D at 34 weeks, measured in a single batch (Diasorin Liaison). Results: 25(OH)D at 34 weeks’ gestation was higher in the women randomised to vitamin D [mean(SD): 67.7 (21.3) nmol/l] compared with placebo [43.1 (22.5) nmol/l, p