THYROID DISORDER DUE TO HIGH INTAKE OF IODINE: REVIEW

Abstract

Iodine is essential for thyroid hormone synthesis. Iodine is a micronutrient essential for the production of thyroid hormones. Iodine deficiency is the most common cause of preventable mental impairment worldwide. Most healthy individuals can tolerate some iodine excess, but not all. Overuse of iodine may sometimes precipitate hyperthyroidism, hypothyroidism, goiter, and/or thyroid autoimmunity in some individuals. People who already have hyperthyroidism, hypothyroidism, goiter, and/or thyroid autoimmunity and are also iodine deficient may be more susceptible to thyroid disorders due to increased iodine intake. Thyroid impairment is usually mild, but iodine-induced hyperthyroidism can be life-threatening in some individuals. Iodine overdose has been reported in iodised salt, drinking water, cow and buffalo milk, some seaweeds, iodine-rich dietary supplements and combinations of these sources may produce iodine excess. The average urinary iodine concentration (UIC) of a population reflects total iodine intake from all sources and can accurately identify populations with excessive iodine intake. Our review describes the relationship between excess iodine intake and thyroid function. We outline potential sources of excess iodine intake and the physiological responses and consequences of excess iodine intake. We provide guidance on the choice of biomarkers to assess iodine intake, with an emphasis on UIC and thyroglobulin. Universal salt iodization (USI) has been introduced in many countries as a cost-effective and sustainable way to eliminate iodine deficiency disorders for more than 25 years.