Impact of Vitamin D Supplementation during Lactation on Vitamin D Status and Body Composition of Mother-Infant Pairs: A MAVID Randomized Controlled Trial

Randomized controlled trial in healthy, term, Caucasian lactating mother-infant pairs recruited in Warsaw, Poland. A total of 174 mothers were randomized 1:1, and 137 were analyzed for the primary outcome (70 in the 1200 IU/d group and 67 in the 400 IU/d group).

Lactating mothers received oral vitamin D3 (cholecalciferol) for 6 months starting about 3 weeks postpartum. The low-dose arm took 400 IU/d total (400 IU vitamin D3 in a multivitamin tablet plus placebo capsule), and the higher-dose arm took 1200 IU/d total (400 IU vitamin D3 in a multivitamin tablet plus an 800 IU cholecalciferol capsule); intake was twice daily. All infants also received 400 IU/d cholecalciferol orally.

Higher-dose maternal vitamin D3 improved maternal vitamin D status more than 400 IU/d, but neither dose fully corrected deficiency and there was no benefit for infant vitamin D status, bone mass, or body composition. Maternal 25(OH)D at 6 months was 25.6 ng/mL with 400 IU/d versus 23.1 ng/mL with 1200 IU/d, P = 0.009, while maternal 25(OH)D <20 ng/mL at 6 months was 29.9% versus 14.3%, P = 0.028. Infants' 25(OH)D increased with their own supplementation, but between-group differences were not significant (group x time interaction P = 0.12; group effect P = 0.45). Maternal and infant iPTH, calcium measures, and DXA-derived bone and body composition outcomes did not differ significantly between groups, and no hypercalcemia occurred.

The trial had modest effective sample size after attrition, with 174 randomized and 137 analyzed for the primary outcome. Follow-up was limited to 6 months and the population was restricted to healthy Caucasian women in Warsaw, which limits generalizability. All infants received vitamin D supplementation, which reduces the ability to isolate maternal supplementation effects on infant outcomes.