Effect of small doses of iodine on thyroid function in patients with Hashimoto's thyroiditis residing in an area of mild iodine deficiency

Abstract

Objective: Several studies have suggested that iodine may influence thyroid hormone status, and perhaps antibody production, in patients with autoimmune thyroid disease. To date, studies have been carried out using large amounts of iodine. Therefore, we evaluated the effect of small doses of iodine on thyroid function and thyroid antibody levels in euthyroid patients with Hashimoto's thyroiditis who were living in an area of mild dietary iodine deficiency.Methods: Forty patients who tested positive for anti-thyroid (TPO) antibodies or with a moderate to severe hypoechogenic pattern on ultrasound received 250 mg potassium iodide daily for 4 months (range 2-13 months). An additional 43 patients positive for TPO antibodies or with hypoechogenicity on ultrasound served as a control group. All patients were TBII negative. Results: Seven patients in the iodine-treated group developed subclinical hypothyroidism and one patient became hypothyroid. Three of the seven who were subclinically hypothyroid became euthyroid again when iodine treatment was stopped. One patient developed hyperthyroidism with a concomitant increase in TBII titre to 17 U/l, but after iodine withdrawal this patient became euthyroid again. Only one patient in the control group developed subclinical hypothyroidism during the same time period. All nine patients who developed thyroid dysfunction had reduced echogenicity on ultrasound. Four of the eight patients who developed subclinical hypothyroidism had TSH concentrations greater than 3 mU/l. In 32 patients in the iodine-treated group and 42 in the control group, no significant changes in thyroid function, antibody titres or thyroid volume were observed. Conclusions: Small amounts of supplementary iodine (250 mg) cause slight but significant changes in thyroid hormone function in predisposed individuals.

Variation in thyroid function in subclinical hypothyroidism: importance of clinical follow-up and therapy

“…This may indicate an additive effect of an increase in iodine intake and a surge in thyroid autoimmunity on thyroid failure in patients with SCH. Supplementary iodine given to individuals with euthyroid Hashimoto's thyroiditis has previously been associated with increased risk of a decline in thyroid function without change in thyroid autoimmunity (44), whereas serum TSH and TPO-Ab increased in some patients with euthyroid endemic goitre treated with potassium iodide (45).…”

Serum TSH and serum thyroid peroxidase antibody fluctuate in parallel and high urinary iodine excretion predicts subsequent thyroid failure in a 1-year study of patients with untreated subclinical hypothyroidism

“…Bournaud & Orgiazzi (27) reviewed the topic, and concluded that from a populationbased perspective iodine sufficiency favours occurrence of autoimmune thyroid disease, but the effect of iodine administration appears to depend on several factors, such as iodine status of the recipient, dose of administered iodine, degree of stimulation of the thyroid gland and genetic factors. Reinhardt et al (11) gave, in a randomised controlled study, a small amount of iodine to individuals with euthyroid Hashimoto's thyroiditis. The study subjects lived in a mildly iodine-deficient area.…”

“…In intervention studies, it has been found that excessive iodine intake may worsen hypothyroidism in individuals with autoimmune thyroiditis (11,12), and it may be speculated that variation in dietary iodine intake may influence thyroid function in patients with SH.…”

Effect of Iodized Oil Treatment on the Development of Thyroid Autoimmunity in Adolescent Females

“…The sera were stored at -20°C and at the end of the study, they were transported frozen to Cardiff (UK) for autoantibody assay. Autoantibodies to Tg and to TPO were measured using a highly sensitive direct assay 6 and TSH receptor antibodies (TRAb) 7 assay. Serum TSH and free T 4 were also measured (Amerlite System).…”