Exploring vitamin D levels and the impact of vitamin D supplementation in pregnant women with diabetes: meta-analysis

Gestational diabetes mellitus (GDM) poses substantial risks to maternal and neonatal health, with a rising global prevalence. Emerging evidence suggests that vitamin D deficiency may contribute to the development of GDM. This meta-analysis aimed to evaluate the association between serum vitamin D levels and GDM, as well as the effects of vitamin D supplementation in pregnant women with diabetes. A comprehensive systematic search of the Web of Science, PubMed, Scopus, and Cochrane databases was conducted through December 2024. Randomized controlled trials and observational studies involving pregnant women with GDM were included. Vitamin D supplementation was initiated during pregnancy, primarily in the second trimester, with dosages ranging from 400 IU/day to 50,000 IU/week. Risk of bias was assessed using the Cochrane Collaboration tool. Of the 2,250 identified articles, 68 studies met the inclusion criteria. A pooled analysis demonstrated significantly lower serum vitamin D levels in women with GDM compared with controls (Hedges’ g = − 0.45; 95% CI: −0.65 to − 0.25). In intervention studies, vitamin D supplementation significantly increased serum vitamin D levels compared with placebo (Hedges’ g = 1.38; 95% CI: 0.72 to 2.03), with a similarly significant improvement observed when comparing pre- and post-intervention levels (Hedges’ g = 1.74; 95% CI: 1.06 to 2.41). Vitamin D supplementation appears effective in correcting vitamin D deficiency among pregnant women with GDM and may improve metabolic outcomes. Further research is warranted to determine optimal dosing regimens, timing of supplementation during pregnancy, and the underlying biological mechanisms linking vitamin D status to glucose metabolism and insulin resistance in GDM.