Iodine/iodide deficiency

A second dietary trace element, selenium, is also essential for normal thyroid hormone metabohsm. Selenium in the form of selenocysteine is a required component for three enzymes that remove iodide from thyroid hormones. Deiodination is the major metabohc pathway by which T4 and T3 are cleared from the system. After secretion by the thyroid gland, T4 may be deiodinated to yield either T3 or the physiologically inactive reverse Tj (3,3, 5 -triiodothyronine, or rX3). T3 and rTj are further deiodinated to form less active metabolites. Selenium, like iodine, is deficient in many areas of the world. 

Goiter due to iodide deficiency is best managed by prophylactic administration of iodide. The optimal daily iodide intake is 150-200 meg. Iodized salt and iodate used as preservatives in flour and bread are excellent sources of iodine in the diet. In areas where it is difficult to introduce iodized salt or iodate preservatives, a solution of iodized poppy-seed oil has been administered intramuscularly to provide a long-term source of inorganic iodine. 

Iodine is concentrated in humans by the thyroid gland to form the iodo-amino acid thyroxine, which is essential to normal health and development. Iodine is a rather rare element (crustal abundance 0.00003 weight %, cf. Table 1.1), so the thyroid gland has become very efficient at scavenging iodide ion. As iodine is deficient in the diet in some locations, a small amount of iodide ion is routinely added to commercial table salt ( iodized salt ). 

Some degree of iodine dietary deficiency was estimated to affect 750 million people in the developing world in 1990 with around 10 million were suffering from stunted growth and mental retardation. In 1993 the WHO published a database of iodine deficiency based on the number of goitre victims in 121 countries where the element was in short supply. This shortage was most prevalent where soils have suffered repeated glaciations or heavy rainfall which had removed most of the iodide that may once have been present, because this is a particularly soluble material and so easily washed away. Those most at risk lived in India and China. 

Mineral waters containing at least 5 mg of iodides are called iodine (iodide) waters. They are important in the treatment of some forms of tuberculosis and positively influence the function of glands with internal secretion. Deficiency of iodine causes hypertrophy of the thyroid gland. 

Our research (e.g., Williams et al., 2004, 2005 Murphy et al., 2004 Hume et al., 2004 Richard et al., 1998 Ibrahim et al., 2003 Simpson et al., 2005) indicates that there are three potentially modifiable factors contributing to transient hypothyroxinemia infection and other illnesses of prematurity, certain drugs and iodine insufficiency of parenteral nutrition. Of the three factors, primary correction of iodide deficiency is essential to allow physiologically appropriate responses before correction of other modifiable factors. As universal T4 supplementation is detrimental in some groups (van Wassenaer et at, 1997b), it is not until the modifiable factors have been corrected or minimized that a trial of T4 supplementation is warranted in extreme preterms, and then only in those who are biochemically hypothyroxinemic. The necessary pilot work has been completed to allow a UK multicenter randomized controlled trial of iodide supplementation to take place safely. 

More detailed studies are needed to investigate these mechanisms. However veterinary medicin studies demonstrating an accelerated iodine absorption in iodine deficient pig and a iodine / iodide excretion in bovine milk provide very interesting preclinical data. 

Iodine occurs to a minute extent (less than 0.001 %) in sea water, but is found in greater concentration, combined in organic form, in certain seaweeds, in oysters and in cod livers. Crude Chile saltpetre, or caliche contains small amounts of sodium iodate, NalOj. from which iodine can be obtained (see below). Some insoluble iodides, for example liiose of silver and mercury(II), occur in Mexico. Iodine is found in the human body in the compound thyroxin in the thyroid gland deficiency of iodine in diet causes enlargement of this gland (goitre). 

It is difficult to define the normal range of iodine intake in humans, and despite efforts to provide iodine supplementation in many geographic areas of the world, endemic iodine deficiency and attendant goiter remain a world health problem (147). Exposure to excess iodine may sometimes lead to the development of thyroid disease. This unusual type of iodide-induced goiter has been found, for example, in 10% of the population of a Japanese island where fishermen and their families consume large quantities of an iodine-rich seaweed and have an iodine intake as high as 200 mg/d (148). 

Iodized Salt. Iodized table salt has been used to provide supplemental iodine to the U.S. population since 1924, when producers, in cooperation with the Michigan State Medical Society (24), began a voluntary program of salt iodization in Michigan that ultimately led to the elimination of iodine deficiency in the United States. More than 50% of the table salt sold in the United States is iodized. Potassium iodide in table salt at levels of 0.006% to 0.01% KI is one of two sources of iodine for food-grade salt approved by the U.S. Food and Dmg Administration. The other, cuprous iodide, is not used by U.S. salt producers. Iodine may be added to a food so that the daily intake does not exceed 225 p.g for adults and children over four years of age. Potassium iodide is unstable under conditions of extreme moisture and temperature, particularly in an acid environment. Sodium carbonate or sodium bicarbonate is added to increase alkalinity, and sodium thiosulfate or dextrose is added to stabilize potassium iodide. Without a stabilizer, potassium iodide is oxidized to iodine and lost by volatilization from the product. Potassium iodate, far more stable than potassium iodide, is widely used in other parts of the world, but is not approved for use in the United States. 

Potassium iodide is added as a nutrient to prevent goiter, a thyroid problem caused by lack of iodine, and to prevent a form of mental retardation associated with iodine deficiency. A project started by the Michigan State Medical Society in 1924 promoted the addition of iodine to table salt, and by the mid-1950s three-quarters of U.S. households used only iodized salt. Potassium iodide makes up 0.06 percent to 0.01 percent of table salt by weight. Sometimes cuprous iodide—iodide of copper—is used instead as the source of iodine. 

When iodine dissolves in organic solvents, it produces solutions having a variety of colors. These colors arise from the different interactions between the I2 molecules and the solvent (Fig. 15.21). The element is only slightly soluble in water, unless I ions are present, in which case the soluble, brown triiodide ion, I,, is formed. Iodine itself has few direct uses but dissolved in alcohol, it is familiar as a mild oxidizing antiseptic. Because it is an essential trace element for living systems but scarce in inland areas, iodides are added to table salt (sold as iodized salt ) in order to prevent an iodine deficiency. 

You have been sent to India to investigate the occurrence of goiter disease attributed to iodine deficiency. As part of your investigation, you must make field measurements of traces of iodide (.I-) in groundwater. The procedure is to oxidize (I-) to I2 and convert the I-, into an intensely colored complex with the dye brilliant green in the organic solvent toluene. 

Potassium iodide and potassium iodate are commonly added to table salt to prevent iodine deficiency and associated thyroid disease. 

The complexity of the interaction between iodine intake and autoimmune thyroid disease has been highlighted by reports of evidence that iodide (compared with thyroxine) induces thyroid autoimmunity in patients with endemic (iodine deficient) goiter (43), while in those with pre-existing thyroid autoimmunity, evidenced by the presence of antithyroid (thyroid peroxidase) antibodies, administration of iodine in an area of mild iodine deficiency led to subclinical or overt hypothyroidism (44). 

Sodium and potassium iodides find limited use as expectorants but a much more important use is as additives, at levels around 5—100 fig/g to table salt in many countries as a prophylactic against goitre. This is a condition arising from iodine deficiency with the result that there is insufficient synthesis of the iodine-containing amino acids, thyroxine and 3,3, 5-triiodothyronine, that are essential components of the... 

The toxicological hazard of perchlorate salts may depend on the cation in the compound. In general, the salts should be considered as skin irritants and treated as such. Perchlorate ion, C104, may compete physiologically with iodide ion, U. This can occur in the uptake of iodide by the thyroid, leading to the biosynthesis of thyroid hormones. As a consequence, perchlorate can cause symptoms of iodine deficiency. 

Iodine is necessary for the proper function of the thyroid gland in humans. Dietary deficiencies can be avoided by the occasional consumption of seafood or by using iodized salt, which combines common table salt (NaCl) with potassium iodide (KI). Iodine is a useful antiseptic, either as tincture of iodine (an alcohol solution of I2), or as an aqueous solution of provi-done iodine (Betadine). see also Halogens Inorganic Chemistry. 

Or, to put it more positively, by adding small amounts of iodide to common salt we can prevent the medical condition known technically as cretinism, a life-long affliction of innately low intelligence caused by iodine deficiency, and which causes permanent brain damage. Nor does this simple dietary requirement cost very much. To provide all 6.5 billion people on the planet with the 70 micrograms of iodine they need every day would require only 166 tonnes of iodine per year, which represent a mere 2% of the iodine the world produces annually. This is an amount that chemists could easily extract from seaweed, making it a sustainable resource, and indeed this was once the way they obtained this remarkable element. 

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