Iodine biological function

The accompanying table lists the essential elements in the human body. Of special interest are the trace elements, such as iron (Fe), copper (Cu), zinc (Zn), iodine (I), and cobalt (Co), which together make up about one percent of the body s mass. These elements are necessary for biological functions such as growth, transport of oxygen for metabolism, and defense against disease. There is a delicate balance in the amounts of these elements in our bodies. Too much or too little over an extended period of time can lead to serious illness, retardation, or even death. 

Iodine is an essential element in humans and other mammals, which is used for the synthesis of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). These hormones play a prominent role in the metabolism of most cells of the organism and in the process of early growth and development of most organs, especially brain (Anderson et al., 2000). Besides T3 and T4, reverse T3 (rT3), monoiodotyrosine (MIT), and diiodotyrosine (DIT) are also synthesized and distributed in the body of humans and animals, but only T3 and T4 have a biological function. Iodine in the human body mainly comes through dietary and water intake, and inhalation of atmospheric iodine. Due to low concentrations of iodine in the air (10—20ng/m ), food and water intake form the major source of iodine for adults, while for infants it is milk. The concentration of iodine in foodstuffs is directly related to that in the environment where the foods come from. Iodine deficiency disorders are mainly found in places where the concentration of iodine in the soil and drinking water is very low. In the water, foodsmffs, and... 

Iodine plays an integral role in a diverse array of processes. As such, it exists in a variety of forms reflecting either the environment in which it is found or its biological function. Water,... 

Microminerals—These are the minerals which are needed at levels of a few milligrams daily. Of the 103 known microminerals, 17 exhibit biological function in man and animals. The contribution which milk makes to the essential trace element intake is greatest with respect to zinc and possibly iodine. 

The quality of the experimental evidence for nutritional essentiality varies widely for the ultratrace elements. The evidence for the essentiality of three elements, iodine, molybdenum and selenium, is substantial and noncontroversial specific biochemical functions have been defined for these elements. The nutritional importance of iodine and selenium are such that they have separate entries in this encyclopedia. Molybdenum, however, is given very little nutritional attention, apparently because a deficiency of this element has not been unequivocally identified in humans other than individuals nourished by total parenteral nutrition or with genetic defects causing disturbances in metabolic pathways involving this element. Specific biochemical functions have not been defined for the other 15 ultratrace elements listed above. Thus, their essentiality is based on circumstantial evidence, which most often is that a dietary deprivation in an animal model results in a suboptimal biological function that is preventable or reversible by an intake of physiological amounts of the element in question. Often the circumstantial evidence includes an identified essential function in a lower form of life, and biochemical actions consistent with a biological role or beneficial action in humans. The circumstantial evidence for essentiality is substantial for arsenic, boron, chromium, nickel, silicon, and vanadium. The evidence for essentiality for the... 

Often biological or biochemical functions are not realized over all the time throughout the lifecycle of some organism but rather operate for limited times and occasions such as reproduction, metamorphosis (role of iodine in amphibia), synthesis of hormons or other signaling components or of anti-eating poisons or repellants or detoxification agents like metallothion-eins. In such cases, the autocatalytic order related to... 

Iron, the central element in oxygen transport and utilization, is discussed in Chapter 29. Iodine, a constituent of thyroid hormones, is discussed in Chapter 33. Sodium, potassium, and chloride, which are important for maintaining proper osmolality and ionic strength and for generating the electrical membrane potential, are discussed in Chapter 39. Most of this chapter is devoted to the metabolism of calcium and phosphorus because of their importance in the skeleton and other body systems. Because of its chemical and biological relationship to calcium, magnesium is also covered. The trace elements are surveyed with emphasis on those for which a biochemical function is known. 

Aromatic iodides are important intermediates in the synthesis of functional materials and biologically active compounds.Although various methods for the synthesis of aromatic iodides have been developed, direct iodination of aromatic rings serves as one of the most straightforward routes. 

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