Evaluation of iodine levels in celiac disease and their effects on the thyroid gland

Objective: This study aims to determine iodine sufficiency in celiac disease (CD) and evaluate the relationship between iodine levels and laboratory parameters as well as ultrasonographic findings. Materials and Methods: A total of 45 celiac disease patients (CD) meeting inclusion criteria and 45 healthy controls (HC) who presented to the Gastroenterology Clinic of SDÜ Research and Application Hospital were included in the study. Spot urine samples were collected from both groups to measure urinary iodine. Laboratory parameters and pathology reports were reviewed retrospectively. Both groups were evaluated ultrasonographically for thyroid pathologies. The Sandell-Kolthoff reaction method, recommended by the WHO, was used for urinary iodine measurement. Statistical analyses were conducted using SPSS version 22, and p-values <0.05 were considered significant. Results: Urinary iodine concentrations were similar between the groups and had no diagnostic utility for CD. There was no significant relationship between urinary iodine levels and thyroid function tests, Marsh classification, or celiac autoantibodies. In the CD group, 26.6% had positive thyroid autoantibodies, and 83.3% of these were women. Thyroid parenchymal heterogeneity was more common in women with CD (p=0.038), whereas thyroid volume was higher in men (p=0.005). Urinary iodine concentrations were higher in patients with homogeneous parenchyma compared to those with heterogeneous parenchyma (p=0.028). Thyroid volume in the CD group was significantly higher compared to the HC group (p=0.013). In the CD group, urinary iodine levels increased with better dietary adherence (rho=0.347, p=0.020) and decreased with longer disease duration (rho=0.300, p=0.046). Parathyroid hormone levels were higher (p=0.001) and ferritin levels were lower (p=0.018) in the CD group, and both parameters were found to have diagnostic value for CD. When both groups were analyzed together, urinary iodine levels increased with higher calcium and hemoglobin levels (rho=0.230, p=0.029; rho=0.272, p=0.010). Conclusion: Although urinary iodine levels were similar in both groups, thyroid volume was higher in the CD group, indicating a higher incidence of goiter compared to the general population. Urinary iodine levels were higher in patients with homogeneous thyroid parenchyma. The finding that urinary iodine levels were higher in patients adhering to a gluten-free diet underscores the importance of dietary compliance, while the iodine level was found to be influenced by disease duration. This is the first study to evaluate the relationship between urinary iodine levels and laboratory and ultrasonographic parameters in an adult CD group. Further studies on this topic are needed.