Vitamin D deficiency, insulin resistance and thyroid dysfunction in obese patients: is inflammation the common link?

The aim of this article is to study the possible relation of serum vitamin D concentrations to body mass index (BMI), visceral fat thickness (VFT), insulin resistance (IR), inflammation (serum monocyte chemoattractant protein-1 – MCP-1) and thyroid parameters in obese patients. A total of 158 non-diabetic, obese patients aged 19–68 without a history of thyroid pathology were recruited. Biochemical markers, insulin, 25-OH vitamin D, thyroid parameters (TSH, FT3, FT4, TPO antibodies, TG antibodies) and VFT were measured. Serum MCP-1 evaluated the inflammation. A HOMA-IR cut-off value of 2.5 defined IR. Most patients had severe (70.3%) or moderate (25.3%) vitamin D deficiency. Vitamin D level was negatively associated with BMI (p = .043) and during the cold season with VFT (p = .009). Vitamin D deficiency correlated with Hashimoto's thyroiditis prevalence during the warm season (p = .047) and was a risk factor for its occurrence (p = .021). At 15 ng/mL cut-off value, vitamin D was negatively correlated with MCP-1 (p = .0006). Also, MCP-1 was positive correlated with HOMA- IR (p = .042), TPO-Ab levels (p = .011) and with Hashimoto's thyroiditis (p = .027). MCP-1 was a risk factor for vitamin D deficiency (p < .0001). Our study supports a bidirectional interaction between vitamin D and systemic inflammation in obese patients. Moreover, systemic inflammation is related to the severity and frequency of Hashimoto's thyroiditis. Vitamin D deficiency is the single independent factor associated with Hashimoto's thyroiditis in obese patients.