Evaluation of the relationship between bioavailable vitamin d and remnant cholesterol in type 2 diabetes mellitus patients

The rate of triglyceride-rich lipoprotein increases in diabetic patients. The cholesterol content of triglyceride-rich lipoproteins is called remnant cholesterol (fasting VLDL, IDL, additionally nonfasting chylomicron and their remnants). Vitamin D deficiency asociated with insulin resistance, atherogenic lipid profile and the risk of developing coronary artery disease. 99% of the vitamin D in circulation is transported in dependence on VDBP and albumin and bioavailable vitamin D is defined as albumin-bound and free-form. The aim of our study was to determine the association between bioavailable vitamin D and remnant cholesterol in Type 2 Diabetes Mellitus (T2DM) patients. Our study was designed as a cross-sectional study and was carried out between November 2015 and December 2017. Our study group consisted of two groups of 406 volunteers with T2DM and control group. Samples were taken in the fasting state. By questioning the demographic characteristics and drug use, subjects using lipid-lowering treatment were not included in the study. The diagnosis of Type 2 Diabetes Mellitus was made according to ADA 2016 criteria. Classification of vitamin D levels was done according to the Endocrine Society. HDL, 25(OH)D, free vitamin D and bioavailable vitamin D levels were significantly lower in diabetic patients than in non-diabetic patients while triglyceride, remnant cholesterol and CRP levels were found to be significantly higher. Remnant cholesterol was negatively correlated with vitamin D, free vitamin D and bioavailable vitamin D in non-diabetic patients and this relationship was impaired in the presence of T2DM. Furthermore, in non-diabetic individuals, CRP was positively correlated with triglyceride, remnant cholesterol, and nonHDL. But this relationship has not been established in patients with Diabetes Mellitus. VDBP was positively correlated with CRP and remnant cholesterol in diabetic patients, but not in non-diabetic patients. Cut-off values were determined from non-diabetic volunteers: 3,56 ng / mL for bioavailable vitamin D and 26,56 mg / dL for remnant cholesterol. In the control group, remnant cholesterol concentrations were found above the cut-off value at 41,2% of individuals with low bioavailable vitamin D and 24,3% with high bioavailable vitamin D. But there was no significant relationship was found in DM group. Logistic regression analysis showed that for increasing remnant cholesterol above the cut-off value, the odds ratio was determined as 2 for bioavailable vitamin D and 1,1 for CRP. But in T2DM, there was no significant relationship for variables. It was observed that in all subjects, bioavailable vitamin D increased the remnant cholesterol cut-off by 2,19 fold; independent of diabetes. However, there was no significant risk for 25(OH)D insufficiency. As a result; low bioavailable vitamin D was found to be a risk factor for elevated remnant cholesterol. However, this relationship was not detected in patients with Diabetes Mellitus. We believe that the inflammation observed in Diabetes Mellitus may increase the concentrations of VDBP and a decrease bioavailable vitamin D levels. Therefore, the bioavailable vitamin D calculated by VDBP, can be useful for clarifying the true vitamin D status.