How does iodine intake affect thyroiditis (Thyroid Autoimmune Hashimoto's)?

From the Guidelines

Iodine intake should be moderate in patients with Hashimoto's thyroiditis, as excessive intake can induce autoimmune thyroiditis and worsen thyroid autoimmunity, while insufficient intake can lead to hypothyroidism and goiter. The relationship between iodine and thyroiditis is complex, and both excessive and insufficient iodine can be problematic 1. For patients with Hashimoto's thyroiditis, it's generally recommended to maintain moderate iodine intake, avoiding both deficiency and excess. Most adults need about 150 micrograms of iodine daily, which can typically be obtained through a balanced diet including iodized salt, seafood, dairy products, and some vegetables. Patients with Hashimoto's should avoid high-dose iodine supplements (over 500 micrograms daily) and iodine-rich foods like kelp or seaweed supplements unless specifically prescribed by their healthcare provider. Excessive iodine can trigger or worsen thyroid autoimmunity by increasing thyroid antigen production and promoting inflammatory responses within the thyroid gland, as chronic exposure to excess iodine intake induces autoimmune thyroiditis, partly because highly iodinated thyroglobulin is more immunogenic 1. Conversely, severe iodine deficiency can lead to hypothyroidism and goiter. Some key points to consider include:

• Clinical signs of toxicity from excessive iodine intake include abdominal pain, loss of appetite, metallic taste in mouth, coughing, fever, delirium, diarrhea, gum and tooth soreness, and vomiting 1
• In iodine-sufficient individuals, excess iodine intake is most associated with elevated blood concentrations of TSH, lower levels of thyroid hormones, and increased thyroid autoimmunity, leading to hypothyroidism and goiter 1
• Patients already taking levothyroxine for Hashimoto's should maintain consistent iodine intake to avoid fluctuations in thyroid function. Before making any significant changes to iodine consumption, patients should consult with their endocrinologist or healthcare provider who can provide personalized guidance based on their specific condition and thyroid status.

From the Research

Iodine Intake and Thyroid Autoimmune Hashimoto's (TAH)

• Iodine is essential for thyroid hormone synthesis, but high iodine intakes may precipitate hyperthyroidism, hypothyroidism, goiter, and/or thyroid autoimmunity in some individuals 2.
• Excess iodine intake has been associated with an increased risk of autoimmune thyroid disease (ATD), particularly thyroiditis, in susceptible individuals 3.
• The relationship between iodine intake and thyroid autoimmune Hashimoto's (TAH) is complex, and high iodine intakes may exacerbate existing thyroid conditions or trigger new ones in predisposed individuals 4.

Effects of Iodine Intake on TAH

• Small doses of iodine (250 μg) can cause slight but significant changes in thyroid hormone function in individuals with Hashimoto's thyroiditis, leading to subclinical hypothyroidism or hyperthyroidism 5.
• Increased iodine intake has been linked to a higher incidence of overt hypothyroidism, subclinical hypothyroidism, and autoimmune thyroiditis in regions with more than adequate or excessive iodine intake 6.
• Iodine-induced hyperthyroidism can be life-threatening in some individuals, and thyroid dysfunction due to excess iodine intake is usually mild and transient, but can be severe in certain cases 2.

Mechanisms of Iodine-Induced TAH

• The mechanisms underlying the development of TAH in response to excess iodine intake are not fully understood, but may involve the enhancement of thyroglobulin immunogenicity, direct toxic effects of excess iodide on the thyroid gland, and the initiation of inflammatory and immune responses 3.
• Genetic predisposition and environmental factors, such as iodine intake, may contribute to the development of TAH, and the relationship between iodide intake and autoimmune hyperthyroidism is less clear 3.