Vitamin D Supplementation During Pregnancy: Effect on the Neonatal Immune System in a Randomized Controlled Trial

Background: Programming of the immune system during fetal development can influence asthma-related risk factors and outcomes in later life. Vitamin D is a well-recognized immune modulator, and deficiency of this nutrient during pregnancy is hypothesized to influence disease development in offspring.

Objective: We sought to investigate the effect on neonatal immunity of maternal supplementation with 4400 IU/d vitamin D during the second and third trimesters of pregnancy by using a subset of cord blood samples from a randomized, double-blind, placebo-controlled clinical trial (the Vitamin D Antenatal Asthma Reduction Trial).

Methods: Cord blood samples from neonates born to mothers supplemented with 4400 IU/d (n = 26) or 400 IU/d (n = 25) of vitamin D were analyzed for immune cell composition by flow cytometry, Toll-like receptor (TLR) expression by quantitative PCR, and cytokine secretion after stimulation with mitogenic, TLR, and T-cell stimuli by cytometric bead array. Responsiveness to the glucocorticoid dexamethasone was determined.

Results: Supplementation of mothers with 4400 IU of vitamin D resulted in an enhanced broad-spectrum proinflammatory cytokine response of cord blood mononuclear cells to innate and mitogenic stimuli (P = .0009), with an average 1.7- to 2.1-fold increase in levels of several proinflammatory cytokines (GM-CSF, IFN-γ, IL-1β, IL-6, and IL-8) across stimuli, a higher gene expression level of TLR2 (P = .02) and TLR9 (P = .02), a greater than 4-fold increase in IL-17A (P = .03) production after polyclonal T-cell stimulation, and an enhanced IL-10 response of cord blood mononuclear cells to dexamethasone treatment in culture (P = .018).

Conclusion: Vitamin D exposure during fetal development influences the immune system of the neonate, which can contribute to protection from asthma-related, including infectious, outcomes in early life.