Abstract
The present review deals with the functional roles of iodine and its metabolism. The main biological function of iodine concerns its role in the biosynthesis of thyroid hormones (THs) by the thyroid gland. In addition, however, further biological roles of iodine have emerged. Precisely, due to its significant action as scavenger of reactive oxygen species (ROS), iodine is thought to represent one of the oldest antioxidants in living organisms. Moreover, iodine oxidation to hypoiodite (IO−) has been shown to possess strong bactericidal as well as antiviral and antifungal activity. Finally, and importantly, iodine has been demonstrated to exert antineoplastic effects in human cancer cell lines. Thus, iodine, through the action of different tissue-specific peroxidases, may serve different evolutionarily conserved physiological functions that, beyond TH biosynthesis, encompass antioxidant activity and defense against pathogens and cancer progression.
Highlights
Sources of Dietary IodineIodine content in food is highly variable, and is low in the majority of food and beverages
The iodine quantity is mostly influenced by its presence in the soil, as well as by iodinecontaining compounds employed in irrigation and fertilizers, and may vary from 10 μg per kg for plants grown on iodine deficient soils to 1 mg per kg for plants grown on iodine sufficient soils [1,17,20]
At the outer surface of the apical membranes of thyrocytes, the biosynthesis of THs is initiated by thyroid peroxidase (TPO), which uses H2O2 produced by DUOX2 to oxidize iodide to iodine radicals and incorporates it on specific tyrosine residues within thyrocyte-secreted thyroglobulin (Tg) molecules [57]
Summary
Iodine content in food is highly variable, and is low in the majority of food and beverages. The iodine quantity is mostly influenced by its presence in the soil, as well as by iodinecontaining compounds employed in irrigation and fertilizers, and may vary from 10 μg per kg for plants grown on iodine deficient soils to 1 mg per kg for plants grown on iodine sufficient soils [1,17,20] This in turn affects the dietary iodine intake of beef cattle, ovine animals, and poultry, together with iodine-enriched supplements, which are used in animal feed and salt licks [20]. Originally limited to Asian countries, has entered the global food market, representing a new source of iodine intake for Western populations [28]. It is worth mentioning, that eating too much seaweed that is rich in iodine could be detrimental to thyroid function [29]. Secretion in milk is performed by the CFTR, anoctamin-1 (ANO1), and PENDRIN iodide transporters, localized in the apical side of the cell membrane [4]
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