Vitamin D supplementation during pregnancy: Improvements in birth outcomes and complications through direct genomic alteration.

Pregnancy represents a time of rapid change, including dramatic shifts in vitamin D metabolism. Circulating concentrations of the active form of vitamin D-1,25(OH)2D skyrocket early in pregnancy to levels that would be toxic to a nonpregnant adult, signaling a decoupling of vitamin D from the classic endocrine calcium metabolic pathway, likely serving an immunomodulatory function in the mother and her developing fetus. In this review, we summarize the unique aspects of vitamin D metabolism and the data surrounding vitamin D requirements during this important period. Both observational and clinical trials are reviewed in the context of vitamin D's health effects during pregnancy that include preeclampsia, preterm birth, and later disease states such as asthma and multiple sclerosis. With enhanced knowledge about vitamin D's role as a preprohormone, it is clear that recommendations about supplementation must mirror what is clinically relevant and evidence-based. Future research that focuses on the critical period(s) leading up to conception and during pregnancy to correct deficiency or maintain optimal vitamin D status remains to be studied. In addition, what effects vitamin D has on genetic signatures that minimize the risk to the mother and her developing fetus have not been elucidated. Clearly, while there is much more research that needs to be performed, our understanding of vitamin D requirements during pregnancy has advanced significantly during the last few decades.