In more than 15,000 pregnancies at one US center, the lowest vitamin D levels tracked earlier delivery

What the research found

Study (retrospective). Carol L. Wagner and Anjali G. Borsum at the Medical University of South Carolina report in the Journal of Perinatology (doi 10.1038/s41372-026-02757-z; Medical Xpress 16 September 2026) on more than 15,000 pregnancies at MUSC between 2016 and 2025. Women with the lowest vitamin D levels had the highest risk of preterm birth, and profound deficiency was associated with earlier gestational age at delivery. The authors do not claim the study proves that vitamin D caused the difference. They describe vitamin D as involved in placental development and in how the mother's immune system tolerates a pregnancy, drawing on earlier trials by Wagner and Bruce W. Hollis, and they note that deficiency is common when time outdoors is limited. Sunscreen still matters for skin cancer, they say, and any supplement decision belongs with a clinician. This is not a recommendation to take a high dose, and it is not a treatment for preterm birth. Educational notes.

Evidence level: Human study. A study in people, but an association isn't proof of cause.

Read the original at Medical University of South Carolina / Journal of Perinatology