Effect of vitamin D supplementation on type 2 diabetes biomarkers: an umbrella of interventional meta-analyses

BackgroundVitamin D supplementation exerts several supporting effects on improving glycemic status, however, results are inconclusive. Thus, in the present study, we aimed to conduct an umbrella of meta-analysis regarding the impact of vitamin D on type 2 diabetes (T2DM) biomarkers.MethodsThe Scopus, PubMed, Web of Science, Embase, and Google Scholar online databases were searched up to March 2022. All meta-analyses evaluating the impact of vitamin D supplementation on T2DM biomarkers were considered eligible. Overall, 37 meta-analyses were included in this umbrella meta-analysis.ResultsOur findings indicated that vitamin D supplementation significantly decreased fasting blood sugar (FBS) (WMD = - 3.08; 95% CI: - 3.97, - 2.19, p < 0.001, and SMD = - 0.26; 95% CI: - 0.38, - 0.14, p < 0.001), hemoglobin A1c (HbA1c) (WMD = - 0.05; 95% CI: - 0.10, - 0.01, p = 0.016, and SMD = - 0.16; 95% CI: - 0.27, - 0.05, p = 0.004), insulin concentrations (WMD = - 2.62; 95% CI: - 4.11, - 1.13; p < 0.001, and SMD = - 0.33; 95% CI: - 0.56, - 0.11, p = 0.004), and homeostatic model assessment for insulin resistance (HOMA-IR) (WMD = - 0.67; 95% CI: - 1.01, - 0.32, p < 0.001, and SMD = - 0.31; 95% CI: - 0.46, - 0.16, p < 0.001).ConclusionThis umbrella meta-analysis proposed that vitamin D supplementation may improve T2DM biomarkers.