Effect of Vitamin D on Glucose Homeostasis and Insulin Sensitivity and Resistance in Type 2 Diabetes: A Systematic Review

Context: In recent years, non-bone diseases have been shown associated with vitamin D deficiency, of which type 2 diabetes is a group of metabolic disorders caused by insulin deficiency. Vitamin D deficiency affects the metabolic function of the cells, including beta-pancreatic cells. Regarding the effectiveness of vitamin D to control type 2 diabetes, the present study aimed at reviewing the relationship between vitamin D, glucose homeostasis, and insulin resistance in type 2 diabetes. Evidence Acquisition: In this review, descriptive and analytic studies were analyzed using biochemical tests, questionnaires, and interviews. Using the keywords, such as vitamin D, type 2 diabetes, and insulin resistance, 11 articles, including descriptive-analytic, cross-sectional, case-control and interventional studies published from 1986 to 2018 were included. Results: The levels of 25-hydroxyvitamin D in diabetics, women, and obese people are lower than others, which can indicate the effect of vitamin D on glucose homeostasis. In addition, vitamin D affects intracellular calcium, and, consequently insulin secretion. It can be said that vitamin D deficiency can make calcium unable to regulate insulin secretion. Conclusions: According to the studies, it can be concluded that vitamin D can be effective to prevent and control type 2 diabetes. Also, there is no association between vitamin D and insulin secreted by food and hemoglobin A1c.