MON-363 Influence of iodine status on control of Graves' Disease

Abstract Disclosure: C. Huang: None. S. Yang: None. H. Chen: None. Background: Patients diagnosed of hyperthyroidism are advised to decrease their iodine intake to less than 100 μg per day as suggested by the American Thyroid Association, which is a level 50 μg less than the recommended amount for adults. Nevertheless, whether iodine restriction benefits disease control is uncertain. This study determined the iodine status of patients with Graves’ disease (GD) and explored its impact on disease control. Method: We enrolled patients with newly diagnosed GD at Taipei Veterans General Hospital, Taiwan, between 2019 to 2024 and prospectively followed their thyroid function, thyroid antibodies and clinical parameters at 2 and 4 weeks, 3, 6, and 12 months after diagnosis. Patients were advised to avoid foods with high iodine content. To determine iodine status, one spot urine sample was collected each day for 14 consecutive days since diagnosis of GD and the result was compared to patients with GD in remission and normal healthy controls. The urinary iodine concentration (UIC) was measured by inductively coupled plasma mass spectrometry. Results: A total of 55 newly diagnosed GD patients (74.6% female) with a mean age of 45.3 ± 13.0 years were enrolled. Compared to patients in remission (n=56) and healthy controls (n=108), the median and mean UIC were significantly higher in newly diagnosed GD patients (median UIC: 76.5 ± 49.4 vs. 131.9 ± 80.4 vs. 194.7 ± 139.5 μg/L; mean UIC: 96.0 ± 68.1 vs. 165.5 ± 103.3 vs. 226.0 ± 137.4 μg/L; all P<0.001). Compared to patients with mean UIC ≥200 μg/L, patients with mean UIC < 200 μg/L had lower free T4 levels at 2 weeks (2.6 ± 1.3 vs. 2.0 ± 0.8, P = 0.039) and a higher proportion of patients had reduction of more than half of their TSH receptor antibody levels at 12 months (76.5 vs 100%, P = 0.033). In multivariate analysis, a larger thyroid size (OR: 1.34, 95% CI: 1.025-1.742, p = 0.03) and a higher mean UIC level (OR: 1.01, 95% CI: 1.0001-1.027, p = 0.03) were associated with increased risk for not achieving a 50% reduction in TSH receptor antibody levels at six months. Conclusion: The study demonstrated the influence of iodine status on control of GD and provided evidence for patients to avoid foods with high iodine content. However, given the fact that most of the patient were controlled to a euthyroid state at 3 months, over-iodine restriction may not be necessary. Presentation: Monday, July 14, 2025