Iodine Supplementation: Usage “with a Grain of Salt”

Abstract

Iodine supplementation through salt iodization is a worldwide, effective strategy for preventing iodine deficiency-related problems. Its safety and efficacy profile has been extensively investigated, and benefits far outweigh the potential iodine-induced risks. Moreover, iodine supplementation during pregnancy in order to avoid brain damage in the newborn is considered a mainstay of preventive medicine. Exposure to high amounts of iodine is actually well tolerated in most cases and can be unrecognized. Nevertheless, at-risk individuals may develop thyroid dysfunction even when they are exposed to increases in iodine intake universally considered as safe. Iodine-induced thyroid disorders include thyroid autoimmunity, thyrotoxicosis, iodine-induced goiter, and hypothyroidism. Moreover, a relationship between iodine intake and histotype distribution of differentiated thyroid cancer has been observed, with a progressive shift from follicular to papillary thyroid cancer. To date, evaluating iodine status in a clinical setting has limitations, and assessing the actual risk for each individual can be challenging, since it is influenced by personal history, genetics, and environmental factors. In conclusion, iodine supplementation programs need to be continued and strengthened, but iodine should be used “with a grain of salt,” because a growing number of susceptible individuals will be exposed to the risk of developing iodine-induced thyroid disorders.

Excess iodine intake: sources, assessment, and effects on thyroid function

“…Excessive iodine consumption has been widely described as a risk factor for the development of thyroid autoimmunity . The association between autoimmunity and disease is complex; a diagnosis of autoimmune disease is made using positive antibody titers, yet individuals may have positive titers of autoantibodies and no disease, or disease and a negative titer .…”

“…The definition of iodine “excess” in these individuals, therefore, depends upon previous iodine status. Older persons with nodular goiter having had a longer exposure to iodine deficiency are at highest risk, and living in an iodine‐deficient area has been proposed as a risk factor per se . The degree of effect depends upon the longevity and severity of iodine deficiency, and the degree of increased exposure to iodine …”

“…Thyroid cancer rates have increased dramatically in the last decade; however, this may be due in part to progress in the early detection of microcarcinomas rather than a true increase in incidence . A link between thyroid cancer and excess iodine intakes has been proposed, possibly due to increased oxidative DNA damage . However, to date, there are few data to support this theory.…”

“…57,130,140 Thyroid autoimmunity Excessive iodine consumption has been widely described as a risk factor for the development of thyroid autoimmunity. 6,97,116,141,142 The association between autoimmunity and disease is complex; a diagnosis of autoimmune disease is made using positive antibody titers, yet individuals may have positive titers of autoantibodies and no disease, or disease and a negative titer. 6 Autoimmune, Hashimoto's, or chronic lymphocytic thyroiditis are the most frequent causes of hypothyroidism in iodine-sufficient areas.…”

The Hypothyroid Brain

“…Supplementation of iodine should be done through food. In many countries there is mandatory supplementation of this element in salt [22] . When hypothyroidism is caused by a deficiency of the hormone due to thyroiditis, congenital hypothyroidism or thyroidectomy, the dosage of TSH is set so this hormone is maintained at a regular concentration.…”