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Consequences of excess iodine

Key Points

  • Recommendations for iodine intake in adults who are not pregnant or lactating are 150 µg of iodine a day

  • Excess iodine exposure or ingestion can result in thyroid dysfunction in certain susceptible individuals, but is generally well-tolerated in most people

  • Iodine-induced thyroid dysfunction might be subclinical or overt and either transient or permanent

  • Sources of iodine excess include iodine supplementation to prevent iodine deficiency at a population level, the diet, vitamins and supplements, medications, contrast media and topical iodine

  • Supraphysiologic doses of iodine are appropriate in certain specific medical indications, including its use in the treatment of severe hyperthyroidism before thyroid surgery and as potassium iodide following a nuclear accident

Abstract

Iodine is a micronutrient that is essential for the production of thyroid hormones. The primary source of iodine is the diet via consumption of foods that have been fortified with iodine, including salt, dairy products and bread, or that are naturally abundant in the micronutrient, such as seafood. Recommended daily iodine intake is 150 µg in adults who are not pregnant or lactating. Ingestion of iodine or exposure above this threshold is generally well-tolerated. However, in certain susceptible individuals, including those with pre-existing thyroid disease, the elderly, fetuses and neonates, or patients with other risk factors, the risk of developing iodine-induced thyroid dysfunction might be increased. Hypothyroidism or hyperthyroidism as a result of supraphysiologic iodine exposure might be either subclinical or overt, and the source of the excess iodine might not be readily apparent.

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Figure 1: The Wolff–Chaikoff effect.

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Acknowledgements

A. M. Leung would like to acknowledge the support of NIH grant 7K23HD06855204.

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Correspondence to Lewis E. Braverman.

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Leung, A., Braverman, L. Consequences of excess iodine. Nat Rev Endocrinol 10, 136–142 (2014). https://doi.org/10.1038/nrendo.2013.251

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