Iodine as a potential endocrine disruptor—a role of oxidative stress

PURPOSE: Iodine is an essential micronutrient required for thyroid hormone biosynthesis. However, overtreatment with iodine can unfavorably affect thyroid physiology. The aim of this review is to present the evidence that iodine—when in excess—can interfere with thyroid hormone synthesis and, therefore, can act as a potential endocrine-disrupting chemical (EDC), and that this action, as well as other abnormalities in the thyroid, occurs—at least partially—via oxidative stress. METHODS: We reviewed published studies on iodine as a potential EDC, with particular emphasis on the phenomenon of oxidative stress. RESULTS: This paper summarizes current knowledge on iodine excess in the context of its properties as an EDC and its effects on oxidative processes. CONCLUSION: Iodine does fulfill the criteria of an EDC because it is an exogenous chemical that interferes—when in excess—with thyroid hormone synthesis. However, this statement cannot change general rules regarding iodine supply, which means that iodine deficiency should be still eliminated worldwide and, at the same time, iodine excess should be avoided. Universal awareness that iodine is a potential EDC would make consumers more careful regarding their diet and what they supplement in tablets, and—what is of great importance—it would make caregivers choose iodine-containing medications (or other chemicals) more prudently. It should be stressed that compared to iodine deficiency, iodine in excess (acting either as a potential EDC or via other mechanisms) is much less harmful in such a sense that it affects only a small percentage of sensitive individuals, whereas the former affects whole populations; therefore, it causes endemic consequences.