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Iodine is essential for thyroid hormone synthesis. High iodine intakes are well tolerated by most healthy individuals, but in some people, excess iodine intakes may precipitate hyperthyroidism, hypothyroidism, goiter, and/or thyroid autoimmunity. Individuals with preexisting thyroid disease or those previously exposed to iodine deficiency may be more susceptible to thyroid disorders due to an increase in iodine intake, in some cases at intakes only slightly above physiological needs. Thyroid dysfunction due to excess iodine intake is usually mild and transient, but iodine-induced hyperthyroidism can be life-threatening in some individuals. At the population level, excess iodine intakes may arise from consumption of overiodized salt, drinking water, animal milk rich in iodine, certain seaweeds, iodine-containing dietary supplements, and from a combination of these sources. The median urinary iodine concentration (UIC) of a population reflects the total iodine intake from all sources and can accurately identify populations with excessive iodine intakes. Our review describes the association between excess iodine intake and thyroid function. We outline potential sources of excess iodine intake and the physiological responses and consequences of excess iodine intakes. We provide guidance on choice of biomarkers to assess iodine intake, with an emphasis on the UIC and thyroglobulin.

Original publication

DOI

10.1111/nyas.14041

Type

Journal article

Journal

Ann N Y Acad Sci

Publication Date

06/2019

Volume

1446

Pages

44 - 65

Keywords

iodine, iodine excess, iodized salt, thyroglobulin, thyroid autoimmunity, Adolescent, Adult, Child, Child, Preschool, Guidelines as Topic, Humans, Hyperthyroidism, Hypothyroidism, Infant, Infant, Newborn, Iodine, Middle Aged, Thyroid Function Tests