Background: Type 2 diabetes mellitus is a widespread and common disease of adults. Because of the dangerous complications that can develop, the treatment of diabetes is very important, and researchers have started to investigate the effects of vitamin D, which could play an important role in the treatment of type 2 diabetes due to its beneficial effect on glycaemic parameters. Supportive treatment with vitamin D should therefore be able to improve the quality of life of diabetic patients.
Aim: The aim of this thesis was to review the literature and to conduct a systematic review of the studies to determine whether the data reported in the literature provide evidence that vitamin D supplementation improves glycaemic control in diabetic patients.
Methods: Using a predefined search profile, we searched PubMed and Web of Science databases for English-language studies published between 2001 and 2021. Studies were selected using inclusion and exclusion criteria, according to PRISMA guidelines. Studies had to report on at least one of the selected parameters, namely glycated haemoglobin, fasting plasma glucose and insulin, insulin resistance and insulin sensitivity. We also included some studies reporting on the use of vitamin D combined with calcium in patients with type 2 diabetes.
Results: We included 30 studies that met the inclusion criteria and presented their main characteristics in this systematic review. The investigators found that in most subjects there was no beneficial effect of vitamin D on glycaemic parameters, but in most vitamin D supplementation had a beneficial effect on serum 25-hydroxyvitamin D (25(OH)D) concentrations. No studies reported vitamin D intoxication, meaning that no dose used was too high. We also included those studies that investigated the effects of vitamin D supplementation with calcium, but there were too few to conclude whether this combination could have a beneficial effect on glycaemic parameters in diabetic patients.
Conclusion: In most studies, vitamin D supplementation did not improve glycaemic parameters in diabetic patients, although there are some that have reported beneficial effects. Vitamin D supplementation may improve serum 25(OH)D concentrations, especially in diabetic patients with insufficient or deficient blood vitamin D concentrations. However, there is insufficient evidence to support the use of vitamin D for the supportive treatment of type 2 diabetes, although it is still a possible option. Therefore, such hypotheses need to be tested and proven by studies with more subjects, sufficient doses of vitamin D and longer intervention times.
|