We will search randomized controlled trials published by PubMed, Embase, the Cochrane Library, Web of Science, and the Clinical Trials.gov website from inception to August 2020 on the effects of ascorbic acid supplementation on blood glucose, glycosylated hemoglobin, serum insulin, insulin resistance and other variables in T2DM patients with no language restrictions. This evidence concerns the gene INS and type 2 diabetes mellitus.