Optimal Iodine Supplementation During Antithyroid Drug Therapy for Graves' Disease Is Associated With Lower Recurrence Rates Than Iodine Restriction

Huibin Huang; Yaxiong Shi; Bo Liang; Huiyao Cai; Qingyan Cai; Ruhai Lin

Disclosures

Clin Endocrinol. 2018;88(3):473-478. 

In This Article

Abstract and Introduction

Abstract

Objective 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.

Methods 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 1 month, 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 ± 10.5 years (17–65 years), and the iodine–restricted group included 202 patients (61 males and 141 females) with an average age of 31.9 ± 11.8 years (16–64 years). 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 24 months. Urinary iodine concentration (UIC), thyrotropin receptor antibody (TRAb), free T3 (FT3), free T4 (FT4) and thyrotropin (TSH) of 2 groups were measured every 3 months. The recurrence rates within 12 months after withdrawal of ATD were evaluated.

Results UIC in the iodine–supplemented group was within the recommended range for optimal iodine intake (135–162 μg/L) and was significantly higher than that in iodine–restricted group (30–58 μg/L). Within 12 months 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%.

Conclusion 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.

Introduction

Antithyroid drugs are a cost–effective, noninvasive, therapeutic option for controlling Graves' disease without inducing permanent hypothyroidism and have become the preferred treatment in Asia and Europe.[1] However, the drawback of this treatment is the high recurrence rate after withdrawal of ATD, which can reach 50%–70%.[2,3] High recurrence risk of ATD treatment may be associated with high serum TRAb level and large thyroid gland volume.[4] The role of dietary iodine intake in GD recurrence has also drawn more attention.

Iodine is a key element in thyroid hormone synthesis and an important regulator of thyroid function. Dietary iodine intake has been suggested to affect the efficacy of ATD treatment. Many experimental studies have proven that high iodine level in the thyroid gland would enhance the antigenicity of thyroglobulin (TG) and elevate the level of serum thyroid autoantibodies,[5] which adversely affect management of GD. Additional studies revealed that excessive iodine intake reduced the efficacy of ATD treatment and increased recurrence rate.[6,7] However, recent studies showed that strict limitation of iodine intake neither improved the efficacy of ATD treatment nor decreased the recurrence rate;[8] on the other hand, excessive iodine intake neither decreased the efficacy of ATD treatment nor increased the recurrence rate.[9] Some researchers even tried early high–dose iodine supplement to assist ATD treatment of GD and achieved good efficacy.[10] So, it is still controversial whether limited iodine intake can help improve the efficacy of ATD treatment and reduce the recurrence of GD. Large–scale clinical intervention studies on the effect of iodine intake on the prognosis of GD are needed.

This study aimed to clarify whether optimal iodine supplementation during antithyroid drug therapy for GD is associated with lower recurrence rates than iodine restriction.

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