The role of vitamin D in treating patients with type 2 diabetes mellitus

Vitamin D is a steroid hormone the primary role of which is to maintain adequate blood levels of calcium and phosphorus needed for the normal bone mineralization process. Receptors for vitamin D active form and enzymes involved in its activation have been found in many other body tissues, leading to a conclusion that vitamin D deficiency is connected with the development of many chronic diseases such as hypertension, multiple sclerosis, certain malignant tumors and type 2 diabetes mellitus (T2 DM). Numerous observational studies have shown that patients with T2 DM have lower blood levels of vitamin D compared to healthy subjects. This indicates that vitamin D could play an important role in the pathogenesis of this chronic noncommunicable disease. By monitoring parameters related to glycemic status, insulin secretion and insulin resistance, many researchers tried to answer the question whether vitamin D supplementation could help patients with diabetes better control their disease and prevent the complications. The results were contradictory and failed to provide enough solid evidence for recommending vitamin D supplementation as a therapeutic measure for these patients. However, patients who might benefit from supplementation are those with the increased T2 DM risk or those at the beginning of the disease. In order to assess which group of patients could benefit from such a supplementation, it is necessary to provide well-designed, long-term experimental studies with precisely defined groups of patients (e.g. prediabetes, early T2 DM, etc.), supplemented with sufficiently high vitamin D doses in relevant monitoring periods.