The relationship between vitamin D level and glycemic control in type 2 diabetes mellitus patients

Abstract

Objectives: This study aims to define vitamin D levels in type 2 diyabetes mellitus (DM) patients and to determine the relationship between the vitamin D levels and glycemic control.
Patients and methods: Between January 2012 and June 2014, a total of 320 diabetic patients (180 women, 140 men; mean age 59.8±10.5 years; range 30 to 85 years) were selected to participate in the study. We examined the patients’ diabetes treatment (oral antidiabetic, insulin or diet therapy). We retrospectively scanned their biochemical parameters and saved the data (postprandial/fasting blood glucose, urea, creatinine, total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides, calcium, phosphorus, AST, ALT, urine microalbumin, HbA1c and 25-hydroxyvitamin D [25 (OH) vitamin D] levels). Patients were categorized into three groups according to their vitamin D levels as; ≤20 ng/mL, between 20-30 ng/mL and ≥30 ng/mL. We compared these three groups in terms of biochemical parameters, exposure to sun, smoking and diabetes treatments. We categorized them into two groups according to their HbA1c level as ≤7% and >7%. We also compared the same parameters and vitamin D levels in these two groups.
Results: When the groups were divided according to vitamin D levels, we monitored 274 patients (85.6%) under 20 ng/mL, 37 patients (11.6%) between 20-30 ng/mL and nine patients (2.8%) above 30 ng/mL. There was a statistically significant positive correlation between vitamin D with calcium and ALT values, and a negative correlation with creatinine (p=0.027, p=0.008, p=0.039, respectively). We detected a statistically significant difference between the HbA1c grouped patients’ fasting blood glucose, total cholesterol, triglycerides, LDL cholesterol, microalbuminuria and vitamin D levels (p<0.001, p=0.015, p=0.001, p=0.028, p<0.001, p=0.043, respectively). Compared to the HbA1c ≤7% group, fasting blood glucose, total cholesterol, triglycerides, LDL, and microalbuminuria values were higher in the HbA1c >7% group; while vitamin D value was lower.
Conclusion: A statistical evaluation of HbA1c groups revealed that the vitamin D value in the HbA1c >7% group was lower compared to the HbA1c ≤7% group (p=0.043). Even though we detected a negative correlation between vitamin D and HbA1c levels, this was not statistically significant (p=0.083). Although these findings suggest that vitamin D level to be associated with glycemic control in individuals with diabetes; there is a need for more comprehensive studies to determine a clear relationship between glycemic control and vitamin D.