Vitamin D, Oxidative Stress and Glycaemic Control in Subjects with Type 2 Diabetes Mellitus: Systematic Review

Background: Diabetes mellitus (DM) is a metabolic and chronic disorder which causes high blood glucose concentrations and dysfunctional pancreatic beta-cells characterized by decreased insulin secretion and signalling. Scientific evidence suggests that vitamin D supplementation may help patients with type 2 diabetes mellitus (T2DM) improve glycaemic control, increase insulin secretion and decrease HbA1c concentrations. Additionally, this supplementation improves antioxidant enzyme concentrations, such as superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT) and total antioxidant capacity (TAC). Finally, some studies have reported that supplementation decreases oxidative markers such as malondialdehyde (MDA). Objective: The objective of this study is to review the effect of vitamin D supplementation on glycaemic control and oxidative stress markers in patients with T2DM. Inclusion criteria involved adult patients with T2DM, oral vitamin D supplementation with different dosages and undefined time. Studies including children or animals and with other pathologies were excluded. Methods: This systematic review was conducted following Reporting Items for Systematic Reviews and Meta-Analyses framework (PRISMA) in terms of study selection, data collection, data analysis, and result reporting. Several databases were reviewed from 2013 to 2020: Google Scholar, REDALYC, Scielo, Scopus and PubMed, among others; word combinations and MeSH keywords were used to find scientific evidence on vitamin D supplementation in patients with T2DM and their relationship with oxidative stress. Results: After making a careful selection of the studies according to its title and abstract, 120 articles were selected for reading the full text. Consequently, 21 studies and 1 report were included in this review, including systematic reviews and meta-analyses. Conclusion: Supplementation with vitamin D may help decrease glucose, and glycosylated haemoglobin and improve insulin secretion. Subjects with T2DM have higher oxidative stress concentrations and lower antioxidants than healthy subjects; vitamin D supplementation may help improve oxidative and antioxidant markers.