The role of thyroid dysfunction and vitamin D deficiency in blood glucose regulation in patients with type 2 diabetes mellitus

Introduction and Purpose: Vitamin D is a hormone with vital functions in the body. Vitamin D deficiency causes musculoskeletal diseases besides it has been associated with many systemic diseases. Also, thyroid dysfunctions frequently accompany type 2 DM. In Type 2 DM, HbA1c, fasting blood glucose and postprandial blood glucose are analyzed for evaluate the glycemic state. In this study, we aimed to reveal the role of replacement therapy in diabetes regulation by retrospectively examining fasting/postprandial blood glucose values and HbA1c values at the 3rd and 6th months after replacement therapy given to those with deficiencies in vitamin D among type 2 DM patients. Material and Method: After getting the ethics committee approval at Afyon Health Sciences University Medical Faculty Hospital, type 2 DM patients who applied to the Internal Medicine Policlinic between 2015 and 2019 were evaluated retrospectively. Of these patients, 263 patients who came to the regular control of the 3rd and 6th months and who were tested for 25(OH) vitamin D, free T4, free T3, TSH, HbA1c at the same time were included in the study. In the first application, the individuals that had vitamin D deficiency and received vitamin D treatment and those who had thyroid dysfunction and euthyroid with treatment were evaluated with HbA1c, fasting blood glucose and postprandial blood glucose measurements for the glycemic status. Results: The mean age of the patients included in the study was 57,9 ± 11,6. HbA1c was decreased in the 3rd month follow-up of patients whose vitamin D levels were normal by taking vitamin D deficiency therapy compared to baseline (%7,19±1,9 %6,97±1,8, p=0,023). There was no significant difference between fasting blood glucose and postprandial blood glucose values at 0 and 3 months after vitamin D treatment (p=0,063 p=0,36, respectively). When the initial, 3rd, and 6th month controls were evaluated, HbA1c and fasting blood glucose did not change significantly with vitamin D treatment (p=0,053 p= 0,49). 77 Negative correlation between vitamin D and fasting blood glucose and HbA1c in the 3rd month controls were determined (r = -0,353 p <0,001, r = -0,23 p = 0,016, respectively). Negative correlation between and vitamin D in 6th month controls were determined (r = -0,79 p = 0,004). The patients who had received hypothyroid treatment and were euthyroid at the 3rd month, no significant difference was found for HbA1c, fasting blood glucose and postprandial blood glucose values were comparement (p = 0,202 p = 0,14 p = 0,72, respectively). Discussion: Previously, there has been a relationship between vitamin D and many diseases. In this study, we determined that there was a significant decrease in HbA1c in the 3rd month in type 2 DM patients with vitamin D treatment; In these patients, we also found a negative correlation between 3rd month vitamin D values and HbA1c values. The negative correlation that we found between vitamin D and glycemic parameters is compatible with the literature; it supports that vitamin D contributes positively to diabetes regulation. There was no significant difference in 6th month HbA1c values; The low number of our sample can explain this. It is one of the endocrinopathies that may accompany thyroid dysfunction in patients with type 2 DM. There are many studies in the literature about the effects of hypothyroidism and hyperthyroidism on glycemic parameters. We aimed to show the change of glycemic parameters with treatment in type 2 DM patients with thyroid dysfunction. However, we could not reach the sufficient number of samples due to the fact that DM patients did not come to their 3-month routine controls regularly or the thyroid dysfunction questioning was not performed well in the outpatient clinic. Conclusion: Vitamin D level monitoring is important in diabetic patients. In short-term follow-up with vitamin D replacement, the glycemic parameters of diabetic patients are improved. However, larger patient group and prospective studies with ongoing vitamin D replacement are needed. Because of that our study was retrospective and possible errors of recording the data may have affected our findings.