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

BACKGROUND: Vitamin 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. METHODS: The 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. RESULTS: Our 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). CONCLUSION: This umbrella meta-analysis proposed that vitamin D supplementation may improve T2DM biomarkers. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13098-023-01010-3.