The Effect of Vitamin D3 on Insulin Secretion and Peripheral Insulin Sensitivity in Type 2 Diabetic Patients

Abstract

SUMMARYThe aim of this study was to evaluate the effect of vitamin D3 supplementation on insulin secretion and insulin resistance. Ten females with type 2 diabetes being treated with oral hypoglycaemic agents and with normal serum and urine calcium levels were enrolled in the study. The study was conducted in March, when levels of vitamin D are lowest in our region. The level of plasma 25(OH)D was measured (normal range in winter 25–120 nmol/l). The first (FPIS) and second (SPIS) phases of insulin secretion were studied during IVGTT Peripheral insulin resistance was measured. A group of 17 age‐ and BMI‐matched females with normal glucose tolerance served as a control group. The diabetic patients were treated with cholecalciferol 1332 IU daily for one month. The mean plasma 25(OH)D level was 35.3±15.1 nmol/l at baseline, 70% of patients being vitamin D deficient. After one month of treatment with vitamin D3, the plasma 25(OH)D level increased by a mean of 75.8%; 70% of the patients achieved normal vitamin D levels. FPIS increased significantly by 34.3%, while the change in SPIS of 20.4% was not significant (p>0.8). We found a significant correlation between the change in FPIS and the change in 25(OH)D level after vitamin D3 supplementation (p<0.018). The results showed a decrease of 21.4% in insulin resistance after one month, but the change was not significant. Bearing in mind that the main defects in type 2 diabetes mellitus are reduced FPIS and insulin resistance, and the favourable effect vitamin D3 had on them, we suggest vitamin D3 deficiency may at least partly contribute to the impairment of insulin secretion and probably of insulin action. Our results suggest that vitamin D3 supplementation could be an element in the complex treatment of type 2 diabetes mellitus during the winter.

Vitamin D and Risk of Incident Type 2 Diabetes in Older Adults: An Updated Systematic Review and Meta-Analysis

“…Regarding insulin secretion, beta cells express both VDR and 1 alpha-hydroxylase (Cyp27b1), which catalyzes the activation of 25OHD into 1,25(OH) 2 D, denoting the cell-intrinsic role for VDR [ 75 ]. Nevertheless, even if the relationship between vitamin D levels and islet function is significant, whether vitamin D supplementation can directly ameliorate insulin secretion in humans remains uncertain because intervention clinical trials have reported mixed results [ 75 , 76 , 77 , 78 ]. As regards the ubiquitous expression of VDR, and, in particular, in insulin-sensitive tissues, a study analyzing human and rodent data showed that: (1) 25OHD repletion in insulin-resistant, overweight-to-obese persons was associated with reductions in subcutaneous adipose tissue expression of pro-inflammatory and profibrotic genes, decreased collagen immunofluorescence, and improved hepatic insulin sensitivity as well as worsening trends after six months on the placebo suggesting progressive metabolic effects of 25OHD deficiency.…”

Association between vitamin D and cardiovascular health: Myth or Fact? A narrative review of the evidence

“…79 In addition, it was interesting to find that vitamin D deficiency leads to decline in mitochondrial respiration, resulting in increasing reactive oxygen species (ROS) production, which in turn leads to decreased insulin signaling pathways and decreased GLUT4 gene transcription, leading to IR as well. 80 Whereas some clinical studies showed beneficial effect of vitamin D supplementation on improvement in insulin sensitivity, 81,82 other trials and a meta-analysis did not reveal any significant effect on glucose and insulin metabolism in obese [83][84][85] or overweight nondiabetic elderly subjects. 86…”

Mechanisms Suggesting a Relationship between Vitamin D and Erectile Dysfunction: An Overview

“…In fact, insulin resistance seems to promote hypertension through the increase in sodium reabsorption in the renal tubules, the activation of the sympathetic nervous system, and the alteration of vascular resistance by increasing the concentration of calcium in smooth muscle cells [ 92 ]. Since it has been observed that vitamin D supplementation may reduce insulin resistance [ 93 ], treatment of this condition may be another mechanism by which vitamin D may help reduce blood pressure. According to this theory, a meta-analysis of 26 RCTs on diabetic patients showed that vitamin D supplementation was able to reduce systolic blood pressure values, especially in patients with vitamin D values below 50 nmol/L [ 94 ].…”

“…Finally, insulin resistance increases the production of LDL and triglycerides and reduces the synthesis of HDL [ 123 ]. As mentioned above, vitamin D might decrease insulin resistance counteracting this mechanism [ 93 ].…”