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Consequences of excess iodine
Angela M. Leung and Lewis E. Braverman
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 g 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.
Leung, A.M. & Braverman, L.E. Nat. Rev. Endocrinol. 10, 136142 (2014); published online 17 December 2013; http://www.nature.com/doifinder/10.1038/nrendo.2013.251
Web End =doi:10.1038/nrendo.2013.251
Introduction
Iodine (atomic weight 126.9 g per atom) is a micronutrient that is required for the synthesis of the thyroid hormones. It is a trace element in Earths upper crust and is found primarily in or near coastal areas. For adults who are not lactating or pregnant, the US Institute of Medicine, and jointly by the WHO, United Nations Childrens Fund (UNICEF) and the International Council for the Control of Iodine Deficiency Disorders (ICCIDD), recommend a daily iodine intake of 150 g and state a tolerable upper level (the approximate threshold below which notable adverse effects are unlikely to occur in the healthy p opulation) of 1,100 g per day in adults.1,2
However, iodine is present in concentrations up to several thousandfold higher than these amounts in medications, supplements and in the iodinated contrast agents used for radiologic studies (Box1). In some susceptible indivi duals, the use of these iodinecontaining substances can result in thyroid dysfunction as a result of the high iodine load. In certain circumstances, iodine excess can result in adverse thyroidal effects after only a single exposure to an iodinerich substance.
Measures of iodine excess
Overall iodine levels cannot be reliably measured in indivi duals given the considerable daytoday variation in iodine intake.3...