Occurrence on earth
Iodine naturally occurs in the environment chiefly as dissolved iodide in seawater, although it is also found in some minerals and soils. The element may be prepared in an ultrapure form through the reaction of potassium iodide with copper(II) sulfate. There are also a few other methods of isolating this element. Although the element is actually quite rare, kelp and certain other plants have the ability to concentrate iodine, which helps introduce the element into the food chain as well as keeping its cost down.
Iodine is used in pharmaceuticals, antiseptics, medicine, food supplements, dyes, catalysts, halogen lights and photography.
In areas where there is little iodine in the diet—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, goiter, mental slowing, depression, weight gain, and low basal body temperatures.
Iodine deficiency is also the leading cause of preventable mental retardation, an effect which happens primarily when babies and small children are made hypothyroid by lack of the element. The addition of iodine to table salt has largely eliminated this problem in the wealthier nations, but iodine deficiency remains a serious public health problem in the developing world.
Toxicity of iodine
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. Elemental iodine, I2, is deadly poison if taken in larger amounts; if 2-3 grams of it is consumed, it is fatal to humans.
Precautions for stable iodine
Direct contact with skin can cause lesions, so it should be handled with care. Iodine vapor is very irritating to the eye and to mucous membranes. Concentration of iodine in the air should not exceed 1 mg/m³ (eight-hour time-weighted average).
Consumption of brassicas, such as cabbage, Brussels sprouts, broccoli and cauliflower, increase the requirements for iodine, especially if consumed raw. Soy beans, raw flaxseed, cassava (used in tapioca), sweet potatoes, lima beans, maize and millet also increase the requirements for iodine. Plants grown on soils poor in Iodine may miss this component, so consuming Iodized salt is recommended. If added to boiling water the Iodine from iodized salt disappearsin, so it is better to use it in cold dishes.
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Males 100-300 mg/day
Females 100-300 mg/day
Iodine on Vegansociety
Iodine on wikipedia