Maternal vitamin D status and risk of gestational diabetes mellitus: A systematic review and meta-analysis of prospective cohort studies

Background: No earlier systematic review and meta-analysis have been done on the association between maternal serum vitamin D status and risk of GDM among prospective studies. The current study was done to systematically review prospective cohort studies (with several years of follow-up) on the association between maternal serum vitamin D deficiency or insufficiency and risk of GDM. Methods: Relevant papers published up to January 2020 were searched through PubMed, MEDLINE, SCOPUS, EMBASE, and Google Scholar using suitable keywords. All prospective cohort studies reporting Hazard Ratios (HRs) or Relative Risks (RRs) and 95% Confidence Intervals (CI) for GDM across categories of maternal serum vitamin D status were included. Results: A total of 29 prospective and nested case-control studies were included in the current systematic review, of which 27 studies had sufficient data for the meta-analysis. Individuals with vitamin D deficiency had a 26% greater risk of developing GDM than those with normal serum vitamin D concentrations (OR: 1.26; 95% CI: 1.13, 1.41). In addition, a significant positive association was seen between combined vitamin D insufficiency and deficiency and risk of developing GDM (OR: 1.23; 95% CI: 1.11, 1.35). Dose-response analysis showed a significant U-shaped non-linear association between serum vitamin D concentrations and risk of developing GDM (P < 0.001), such that those with serum vitamin D concentrations between 40 and 90 nmol/L had significantly reduced risk of GDM. Conclusions: We found a significant association between vitamin D deficiency and an increased risk of GDM. The lowest risk of GDM was found among those with a serum vitamin D levels of 40-90 nmol/L. Further studies, including randomized clinical trials, are needed to confirm our findings. Registration: PROSPERO (ID: 180722), https://www.crd.york.ac.uk/prospero/. 0 2021 Published by Elsevier Ltd.