Vitamin D supplementation in pregnancy and lactation to promote infant growth

Multiarm supplementation study in healthy pregnant women in Dhaka, Bangladesh, enrolled at 17-24 weeks' gestation and followed with their infants to 1 year of age. Active intervention groups included prenatal low-, medium-, and high-dose vitamin D3, plus a prenatal and postpartum continuation arm.

Vitamin D3 was given orally at 4,200 IU/week, 16,800 IU/week, or 28,000 IU/week from 17-24 weeks' gestation until birth. One arm continued 28,000 IU/week for 26 weeks postpartum. All participants also received calcium 500 mg/day, iron 66 mg/day, and folic acid 350 micrograms/day.

Maternal vitamin D supplementation from midpregnancy through birth or through 6 months postpartum did not improve infant linear growth or other anthropometric outcomes. The primary endpoint, length-for-age z score at 1 year, was not different across groups (global P = 0.23); mean values were -0.93, -1.11, -0.97, -1.06, and -0.94 across placebo and the four vitamin D groups, respectively. Stunting at 1 year was also similar across groups, ranging from 13.4% to 19.4%. Although vitamin D-related biomarkers changed in a dose-dependent manner, there were no growth benefits; possible hypercalciuria was more frequent with the highest-dose prenatal and postpartum regimen, and hypercalcemia was uncommon.

Interpretation is limited by modest per-arm sample sizes (N = 259-260) and enrollment from a single public hospital in Dhaka, which may limit generalizability beyond healthy pregnant women in this setting. The main clinical endpoints were negative despite biochemical responses, and the highest-dose regimen raised a small safety signal for possible hypercalciuria.