Endocrine Abstracts

Background

Low serum vitamin D concentrations have been associated with autoimmune thyroiditis. Obesity is characterized by lower vitamin D levels and higher risk to develop autoimmune diseases. The aim of the study was to investigate the possible relation of serum vitamin D concentrations to visceral fat thickness (VFT), insulin resistance (IR), inflammation (serum monocyte chemoattractant protein-1 – MCP-1) and thyroid parameters in obese patients.

Materials and methods

A total of 45 non-diabetic, obese patients aged 20–59 years without a history of thyroid pathology were recruited. Biochemical markers, insulin, 25(OH)D, thyroid parameters (thyroid stimulating hormone – TSH, free thyroxine – fT₄, free triiodothyronine – fT₃, thyroid peroxidase antibodies – TPO-Ab, thyroglobulin antibodies – Tg-Ab) and VFT were measured. Serum MCP-1 evaluated the inflammation. A HOMA-IR cut-off value of 3.0 defined IR.

Results

Most patients had vitamin D deficiency (46.7%) and insufficiency (48.9%). Vitamin D level was negatively associated with BMI (P = 0.038) and VFT (P = 0.006). Vitamin D deficiency correlated with autoimmune thyroiditis prevalence (P = 0.032) and was a risk factor for its occurrence (P = 0.023). At 20 ng/ml cut-off value, vitamin D was negatively correlated with MCP-1 (P = 0.007). Also, MCP-1 was positive correlated with HOMA-IR (P = 0.039), TPO-Ab levels (P = 0.015) and with autoimmune thyroiditis (P = 0.028). MCP-1 was a risk factor for vitamin D deficiency (P < 0.001). The final logistic model of a multivariate analysis, performed with autoimmune thyroiditis as the dependent variable and age, BMI category, 25(OH)D category, and TSH levels as the independent ones, showed that patients with autoimmune thyroiditis were more likely to have deficiency of 25(OH)D (P = 0.023) and higher TSH (P < 0.001) levels.

Conclusion

This investigation supports an interaction between vitamin D and systemic inflammation in obese patients. Systemic inflammation is related to the frequency of autoimmune thyroiditis. Vitamin D deficiency is the single independent factor associated with autoimmune thyroiditis in patients with obesity.