Diabetes mellitus is a complex systematic disease caused by a profound or relative incompetence of pancreatic hormone, resulting in a carbohydrate metabolism, developed by an organism. The first stroke of saccharine disease is an increase of glucose concentration in blood, so called hyperglycemia, and, as a result, its urinary excretion (glycosuria). Saccharine disease has two stages: insulin-dependent (I type), and insulin-independent (II type) diabetes. As a general matter, people under the age of 30, an average of 10-15% of the total number of patients, are diagnosed as having type I. One of the causes of diabetes type I is a virus in -cells of islets of Langerhans of the pancreas producing insulin. Type II diabetes (T2D) is a more widespread diagnosis: about 85% of patients suffer from it. Moreover, about 85% of them have a body mass index (BMI) over the normal level. Diabetes is one of the most widespread diseases. It is said to be cureless; thus, it is of current interest to define the ways to eliminate the harm it makes on the organism in order to make the patient’s life easier. This and a variety of other factors put diabetes in rank of major medical and social problems that require an urgent solution.
There are several factors correlated with the disease explained in the contemporary academic sources. However, some issues are paid little attention by scholars. For instance, the sufficiency or deficiency of specific hormones or vitamins in the body can be correlated with various sequels. Vitamin D is said to be one of the most important substances influencing the diabetes proceeding. The present literature review has been performed in order to draw out the relationship between the vitamin D deficiency (VDD) and diabetes of both types. The purpose of the review is to find out whether VDD is a risk factor for related disease formation and if the supplementation of vitamin D is a solution for decreasing diabetes related consequences. The data was collected from peer-reviewed journals reflecting original researches not older than 5-7 years from the present date.
The methodology of all reviewed researches was the same: studies used blood sampling and questionnaire in order to obtain the practical results. Every research was made considering the certain age group; thus, this review collects the data for all age cohorts. Every research described below has the participant’s group diagnosed with diabetes type I or type II and a control group of healthy people. The number of participants depends on the particular research; it varies from 88 to 5,806. The following studies are cross-sectional ones.
The literature review showed that the vitamin D insufficiency is significantly associated with various complications in patients having diabetes. VDD appears to one of the most notable one since it is responsible for the presence of the set of substances in the human organism. VDD is extremely dangerous for children and adolescents because vitamin D takes part in skeleton formation. Furthermore, VDD appears to be the most important cause of type II diabetes formation.
As it was stated above, vitamin D is responsible for a wide variety of processes occurring in the organism. The researches show the relationship between VDD and microalbuminuria, neuropathy and retinopathy development in children and adolescents with type I diabetes diagnosis. 1 The study evidenced that VDD is not associated with microalbuminuria or neuropathy. However, it was found that it is correlated to early retinal vascular damage and retinopathy of children and adolescents. 1
Another study, demonstrated that VDD has a significant influence on the development of child’s skeleton 2. As vitamin D is associated with the process of the bony cage formation, its deficiency may lead to skeletal fragility. Together with diabetes development, VDD makes a vital bone health impact, reduction in bone mineral density and strength, and fracture risk. In addition, the lack of vitamin D means the lack of calcium since is it not digested without vitamin D. Calcium is essential for the child’s skeleton formation; thus, its deficiency creates the bone health problems. The research showed that less than 25 percent of participants were vitamin D sufficient; therefore, the rest are at risk of skeletal fragility. 2
Concerning the adult cohort, the diabetes of both types produces various correlated problems. One among many complications is diabetic neuropathy in type II diabetes 3. This disease is related to the loss of sensitivity within the organism, especially legs. The study proved the direct relationship of vitamin D insufficiency and diabetic peripheral neuropathy development. In addition, the development of neuropathy is related to the duration of diabetes disease. Specifically, the longer the individual is affected with diabetes, the more he/she is likely to develop the VDD, and as a result, neuropathy. 3
As it has been mentioned earlier, there are two types of diabetes. It is generally known that type I diabetes can develop into type II disease. VDD has a direct relation to the development of type II diabetes in the patients having type I diabetes. The study showed that septuagenarians patients with VDD develop the type II diabetes more often that those without VDD.4 Together with vitamin D sufficiency, the BMI, smoking status, concentration of high-density lipoprotein and triacyglycerine concentration was examined. The exploration confirmed the VDD being a risk to type II diabetes development apart from above-indicated factors. The similar study was performed by Szep et al., who also examined the relationship between VDD and type II diabetes. The difference between examinations is the participants’ condition – the HIV-diagnosed individuals were examined. 5. This research also evidenced the direct relationship of VDD and T2D. The patients with HIV develop type II diabetes quicker than those without it.
The VDD also is correlated to the insulin resistance and -cells dysfunction. Vitamin D concentration in human body plays a significant role for insulin sensitivity and -cell functioning. The insulin resistance is said to be a risk to type II diabetes development. According to the research, VDD is associated with both insulin resistance and -cell dysfunction problems 6. In addition, VDD at individuals having obesity are at higher risk of insulin resistance and type II diabetes. High body mass index (BMI) itself is related to diabetes. Combined with VDD, it creates the higher risk for the development of the insulin resistance, and as a result, type II diabetes. 6,7
VDD is responsible for the set of other complex sequels for diabetes. For example, endothelial dysfunction development is related to vitamin D insufficiency. This disease may lead to cardiovascular disease since endothelium is the biggest endocrine gland in the human organism. The research evaluates the importance of vitamin D sufficiency for endothelial progenitor cell number and flow-mediation dilation rate. 8 The authors conducted a cross-sectional study for patients with type II diabetes diagnosis. It has showed than VDD is significantly correlated to the brachial artery flow-mediation dilation and circulating endothelial progenitor cell. This, in its turn, creates a risk to depletion of endothelial progenitor cells and endothelial dysfunction in patients with type II diabetes. It is essential to point out that in this case, the VDD is associated with hemoglobin level as well. 8
Among other complications, microvascular ones should be distinguished. Vitamin D level is connected to the correlation between vitamin D levels and high-sensitivity C-reactive protein, NF?B activity, and TLR4 expression. These factors are closely related to the cardiovascular system functioning. Thus, as it can be seen, the dysfunction of these hormones creates microvascular complications. The research demonstrated that concentration of aforementioned substance is closely related to vitamin D sufficiency. 9 It means the higher is VDD, the lower is the level of these substances, and the higher the risk of microvascular complications development is. Moreover, this study showed the risk of disease inflammation due to VDD.
Along with microvascular complication, VDD may create nephrological problems. Vitamin D is responsible for vitamin D binding protein (VDBP) – megalin ligand. The function of megalin ligand is the transportation a protein for vitamin D metabolic-action product in plasma. Megalin is endocytic receptor, presented in epithelial cells, including kidney cells, is a multiligand receptor with an extensive content of controlling protides formation. The study conducted evidenced that vitamin D concentration is significantly related to VDBP presence in the urine 10 of a patient with diabetes of both types. Therefore, the VDD is contributed to loss of VDBP and the diabetic nephrological consequences in patients.
Making a summary of all reviewed investigations, it should be pointed out that further researches on the matter are essential. There are no specific studies exploring the possibility of vitamin D supplementation in order to decrease a risk of diabetes complications development. At the present moment, the possibility of supplementation for vitamin D and its outcomes were not studied closely, despite it could be a sufficient solution for the group of people at risk.