Therapeutic effects of dietary antioxidative supplements on the management of type 2 diabetes and its complications; umbrella review of observational/trials meta-analysis studies

BACKGROUND: Controversial data on the effects of vitamins (V) and nutrients on the management of type 2 diabetes mellitus (T2DM) is available. Thus, it is aimed to clarify the role of vitamins and nutrients through an umbrella review regarding the available observational/ trials meta-analyses. METHODS: All meta-analyses of observational and clinical trials conducted on the impact of vitamins and nutrients in T2DM published until 5(th) June 2021 in PubMed or Web of Sciences were included in this review. Also, the meta-analysis on children, pregnant women, type 1 DM, or in vivo/in vitro studies was excluded. Search results were reported according to the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) flowchart. RESULTS: The overall of 93 papers (99 studies) consisting of 75 trials and 24 observational studies were included. Most studies were conducted on the effect of VD and alpha-lipoic acid (ALA) in both genders. Consumption of VD or its analogous; 20 IU/d to 450,000 IU/once for 3 weeks to 7 years showed to have a positive effect on the parameters of glucose hemostasis. Moreover, an inverse association was observed between VD level and T2DM risk. Daily consumption of 1200 mg VC for at least 12 weeks improved lipid profile and glucose hemostasis parameters. Furthermore, VB and medications for diabetic polyneuropathy (DPN) increased nerve conduction velocity. Vitamins K and E were showen to not have significant impact on T2DM. ALA had a beneficial effect on DPN symptoms after 2–4 weeks of intake of at least 300 mg/d. T2DM risk was reduced by doubling ALA intake. The effective daily doses of chromium, zinc and coenzyme Q10 on lipid profile and glucose hemostasis parameters were > 200 mg