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

Abstract 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