Evaluating the Effect of Vitamin D Supplementation on Type 2 Diabetes Risk: A Systematic Review

Although observational studies have linked vitamin D deficiency to diabetes, it is unknown if taking vitamin D supplements can reduce the chance of developing type 2 diabetes mellitus (T2DM). The purpose of this systematic review is to determine whether vitamin D supplementation lowers the risk of type 2 diabetes. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used to search for studies based on pre-established inclusion and exclusion criteria. Five different databases (Scopus, Web of Science, PubMed, Google Scholar, and Cochrane Library) were used to search for relevant studies. These databases contained 1,916 relevant research papers that were examined for duplication using the EndNote software. After a careful text analysis, only 13 of these articles were found to be pertinent. The Newcastle-Ottawa Scale (NOS) was used to assess the risk of bias in each included study. Ten of the 13 trials examined how vitamin D supplementation affected the homeostasis model assessment of insulin resistance (HOMA-IR) of the patients. Patients using vitamin D supplements saw a drop in their HOMA-IR in six of these RCTs but an increase in four of them. The vitamin D group had a lower HOMA-IR than the placebo cohort in seven of the 10 trials that examined HOMA-IR. Despite the impact on insulin resistance, there is not enough data to conclude that vitamin D supplement significantly lowers the incidence of T2DM. To impact clinical guidelines about supplementation with vitamin D among people at risk of type 2 diabetes, more studies in this area might be beneficial.