Vitamin D deficiency enhances insulin resistance by promoting inflammation in type 2 diabetes.

Objective: This study was aimed to analyze the level of serum 25(OH)D in patients with type 2 diabetes (T2DM), and explore the relationship between serum 25(OH)D and insulin resistance.

Methods: 60 health people and 106 patients with T2DM were measured the level of serum 25(OH)D, fasting blood glucose, insulin, TNF-α, IL-6, IL-8, and IL-1β, etc. We established a rat model of T2DM and vitamin D (VD) deficiency, and studied the effects of VD deficiency on homeostasis model assessment insulin resistance (HOMA-IR) and pancreatic inflammation.

Results: The level of serum 25(OH)D in patients with T2DM was significantly lower than that in health people, and HOMA-IR decreased with the increasing of the serum 25(OH)D level. Pearson correlation analysis showed that the serum 25(OH)D level in patients with T2DM had a negative correlation with HOMA-IR (r=-0.750, P<0.001), TNF-α (r=-0.705, P<0.001), IL-1β (r=-0.661, P<0.001), IL-8 (r=-0.645, P<0.001), and IL-6 (r=-0.609, P<0.001). In animal experiment, Vitamin D deficiency enhanced HOMA-IR in rats with T2DM and reversed it by supplementing VD. Vitamin D deficiency could increase the inflammatory response by up-regulating p-p65/RelB in the pancreas tissue.

Conclusion: Serum 25(OH)D was elevated and Vitamin D deficiency enhanced insulin resistance by promoting inflammation via NF-kB pathway in patients with T2DM.