Optimal iodine supplementation during antithyroid drug therapy for Graves’ disease is associated with lower recurrence rates than iodine restriction

Abstract

A relationship between iodine intake and the effectiveness of antithyroid drug (ATD) therapy for Graves' disease (GD) has been suggested, and strict restriction of iodine intake has been tried in the treatment of GD in some studies. However, it is unclear whether dietary iodine supplementation improves the prognosis of ATD therapy for GD. This study aimed to clarify whether optimal iodine supplementation during antithyroid drug therapy for GD is associated with lower recurrence rates than iodine restriction. This was a prospective randomized trial of newly diagnosed patients with GD. Patients with newly diagnosed GD were recruited. After ATD therapy and strict dietary iodine restriction for 1month, patients (n=459) were randomly assigned to iodine-supplemented and iodine-restricted groups. After exclusion, 405 patients finally completed the study. The iodine-supplemented group included 203 patients (61 males and 142 females) with an average age of 32.2±10.5years (17-65years), and the iodine-restricted group included 202 patients (61 males and 141 females) with an average age of 31.9±11.8years (16-64years). Patients in the iodine-supplemented group were given about 10 grams of iodized salt every day, while the iodine-restricted group received noniodized salt with low-iodine or noniodine diet. The dietary iodine intervention lasted for 24months. Urinary iodine concentration (UIC), thyrotropin receptor antibody (TRAb), free T3 (FT3), free T4 (FT4) and thyrotropin (TSH) of 2 groups were measured every 3months. The recurrence rates within 12months after withdrawal of ATD were evaluated. UIC in the iodine-supplemented group was within the recommended range for optimal iodine intake (135-162μg/L) and was significantly higher than that in iodine-restricted group (30-58μg/L). Within 12months of withdrawal of ATD, the total recurrence rate in the iodine-supplemented group was 35.5%, significantly lower than in the iodine-restricted group, which was 45.5%. Optimal dietary iodine supplementation during antithyroid drug therapy for GD is associated with lower recurrence rates than iodine restriction, and therefore, diet control with strict iodine restriction might be an adverse factor in the management of GD.