wiki iodine

http://en.wikipedia.org/wiki/Iodine


Structure and bonding
Structure of solid iodine
Crystalline iodine

Iodine normally exists as a diatomic molecule with a I-I bond length of 270 pm, one of the longest single bonds known. The I2 molecules tend to interact via van der Waals forces, and this interaction is responsible for the higher melting point compared to more compact halogens, which are also diatomic. The solid crystallizes in the orthorhombic space group Cmca No 64, Pearson symbol oS8, the same as black phosphorus. The I-I bond is relatively weak, with a bond dissociation energy of 36 kcal/mol. In fact most bonds to Iodine tend to be weaker than for the lighter halides. One consequence of this weak bonding is the relatively tendency of I2 molecules to dissociate into atomic iodine.

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Dietary intake

The daily Dietary Reference Intake recommended by the United States Institute of Medicine is between 110 and 130 µg for infants up to 12 months, 90 µg for children up to eight years, 130 µg for children up to 13 years, 150 µg for adults, 220 µg for pregnant women and 290 µg. for lactating mothers.[30] The Tolerable Upper Intake Level (UL) for adults is 1,100 μg/day (1.1 mg/day).[31] The tolerable upper limit was assessed by analyzing the effect of supplementation on thyroid-stimulating hormone.[29]

The thyroid gland needs no more than 70 micrograms /day to synthesize the requisite daily amounts of T4 and T3. The higher recommended daily allowance levels of Iodine seem necessary for optimal function of a number of body systems, including lactating breast, gastric mucosa, salivary glands, oral mucosa, thymus, epidermis, choroid plexus, etc.[32][33][34] The high iodide-concentration of thymus tissue in particular suggests an anatomical rationale for this role of Iodine in the immune system.[35] The trophic, antioxidant and apoptosis-inductor actions and the presumed anti-tumour activity of iodides has been suggested to also be important for prevention of oral and salivary glands diseases.[36]

Natural sources of iodine include sea life, such as kelp and certain seafood, as well as plants grown on iodine-rich soil.[37][38] Iodized salt is fortified with iodine.[38]

As of 2000, the median intake of iodine from food in the United States was 240 to 300 μg/day for men and 190 to 210 μg/day for women.[31] In Japan, consumption is much higher due to the frequent consumption of seaweed or kombu kelp.[29]

After iodine fortification programs (e.g. iodized salt) have been implemented, some cases of iodine-induced hyperthyroidism have been observed (so called Jod-Basedow disease). The condition mainly seems to occur in people over forty, and the risk appears higher when iodine deficiency is severe and the initial rise in iodine intake is high.[39]

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Deficiency
Main article: Iodine deficiency

In areas where there is little iodine in the diet,[5] typically remote inland areas and semi-arid equatorial climates where no marine foods are eaten, iodine deficiency gives rise to hypothyroidism, symptoms of which are extreme fatigue, goitre, mental slowing, depression, weight gain, and low basal body temperatures.[40] Iodine deficiency is the leading cause of preventable mental retardation, a result which occurs primarily when babies or small children are rendered hypothyroidic by a lack of the element. The addition of iodine to table salt has largely eliminated this problem in the wealthier nations, but as of March 2006, iodine deficiency remained a serious public health problem in the developing world.[41] Iodine deficiency is also a problem in certain areas of Europe. In Germany it has been estimated to cause a billion dollars in health care costs per year.[29]

Other possible health effects being investigated as being related to deficiency include:

* Breast cancer. The breast strongly and actively concentrates iodine into breast-milk for the benefit of the developing infant, and may develop a goiter-like hyperplasia, sometimes manifesting as fibrocystic breast disease, when iodine level are low. Studies indicate that iodine deficiency, either dietary or pharmacologic, can lead to breast atypia and increased incidence of malignancy in animal models, while iodine treatment can reverse dysplasia.[42][43][44] The role of Iodide in breast dysplasia and development of Breast Cancer is an area of active research.[42]

* Stomach cancer. Some researchers have found an epidemiologic correlation between iodine deficiency, iodine-deficient goitre and gastric cancer.[45][46][47] A decrease of the incidence of death rate from stomach cancer after implementation of the effective iodine-prophylaxis has been reported also.[48]


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Precautions and toxicity of elemental iodine

Elemental iodine is an oxidizing irritant and direct contact with skin can cause lesions, so iodine crystals should be handled with care. Solutions with high elemental iodine concentration such as tincture of iodine and Lugol's solution are capable of causing tissue damage if use for cleaning and antisepsis is prolonged.

Elemental iodine (I2) is poisonous if taken orally in larger amounts; 2–3 grams of it is a lethal dose for an adult human.

Iodine vapor is very irritating to the eye, to mucous membranes, and in the respiratory tract. Concentration of iodine in the air should not exceed 1 mg/m³ (eight-hour time-weighted average).

When mixed with ammonia and water, elemental iodine forms nitrogen triiodide which is extremely shock sensitive and can explode unexpectedly.
[edit] Toxicity of Iodide ion

Excess iodine has symptoms similar to those of iodine deficiency. Commonly encountered symptoms are abnormal growth of the thyroid gland and disorders in functioning and growth of the organism as a whole. Iodides are similar in toxicity to bromides.[citation needed]

Excess iodine can be more cytotoxic in the presence of selenium deficiency.[49] Iodine supplementation in selenium-deficient populations is theoretically problematic, partly for this reason.[29]
[edit] Iodine sensitivity

Some people develop a sensitivity to iodine. Application of tincture of iodine can cause a rash. Some cases of reaction to Povidone-iodine (Betadine) have been documented to be a chemical burn.[50] Eating iodine-containing foods can cause hives. Medical use of iodine (i.e. as a contrast agent, see above) can cause anaphylactic shock in highly iodine sensitive patients. Some cases of sensitivity to iodine can be formally classified as iodine allergies. Iodine sensitivity is rare but has a considerable effect given the extremely widespread use of iodine-based contrast media.[51]
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