Iodine is a chemical element that is required for growth and survival. It is found in varying amounts in plants and animals. Iodine is required by the body for the synthesis of thyroid hormones. Most of it is stored in the thyroid gland, located in the front of the neck. Iodine deficiency diseases, including goiter are widespread in many parts of the world and form a major public health problem.
Why should I be aware of it?
Iodine is critical for two aspects of human health -- the proper functioning of the thyroid gland, and the development of the fetus in the womb.
It is an important component of thyroid hormones thyroxine (T4) and triiodothyronine (T3). Thyroid hormones regulate cell metabolism and play a vital role in many physiological functions, including growth, development, metabolism, reproductive function, energy expenditure and normal brain and physical development in growing children. Whenever the levels of thyroid hormones fall, the thyroid gland takes up more iodine from the blood to synthesise these hormones. If iodine is too low in the diet, not only are the thyroid hormones not synthesized, but there is also enlargement of throid gland which is known as goitre.
Iodine is critical for the normal development of the baby in the womb, and an adequate amount of iodine is necessary to prevent miscarriages. Other functions which have been suggested for iodine include use in water purification, as a skin disinfectant, and in proper functioning of the immune system.
All about Iodine
Soil concentration of iodine determines the amount of iodine in most natural foods to a large extent. Iodine is also found in seawater, and marine animals can concentrate iodine from seawater. So, any type of seafood is a rich source of iodine, especially fish and shellfish. Some types of seaweed are also rich in iodine. Yoghurt, cow's milk, eggs, and strawberries are also good sources of this element. Some vegetables contain iodine, but only if they are grown in iodine-rich soils.
Iodized salt (to which iodine has been added) has been universally adopted as the most appropriate measure for iodine supplementation aimed at elimination of iodine deficiency disorders (IDDs). Usually, iodine is added in the form of potassium iodate to salt, as it is more stable than the iodide form. The advantage of using iodized salt is that it has a far reaching effect as it is used by all sections of a community. Iodized oil and iodized bread have also been used for iodine supplementation to a lesser extent.
The Institute of Medicine at the National Academy of Sciences developed new Dietary Reference Intakes for iodine in the year 2000. The recommendations on a daily basis are as follows:
- 1-8 years: 90 microgram (mcg)
- Children 9-13 years: 120 mcg
- Adolescents 14-18 years: 150 mcg
- Adults 19 years and older: 150 mcg
- Pregnant women 14 years and older: 220 mcg
- Lactating women 14 years and older: 290 mcg 
Iodine deficiency is now accepted as the most common cause of preventable brain damage in the world. Iodine deficiency disorders (IDDs) include mental retardation, hypothyroidism, goiter, and varying degrees of other growth and developmental abnormalities. In case of iodine deficiency, an enlargement of the thyroid gland is seen which is called goiter. It is one of the earliest and the most obvious signs of iodine deficiency.
More severe cases of iodine deficiency result in hypothyroidism, a condition with low blood levels of thyroid hormones. Hypothyroidism can manifest as low energy levels, dry or scaly or yellowish skin, tingling and numbness in extremities, weight gain, personality changes, depression, mental slowness and reduced heart function. Iodine deficiency is most damaging to the developing brain in a child. In severe cases of iodine deficiency, a child may be born with cretinism, a condition characterized by severe mental retardation, growth stunting, apathy, and impaired movement, speech or hearing. If discovered in its initial stages, cretinism can be corrected with iodine supplementation.
Goitrogens are substances that interfere with iodine utilization or the production of thyroid hormone. These foods include cruciferous vegetables (cabbage, cauliflower, and broccoli), soy products, cassava root, mustard, and millet. Goitrogens are not too much of a concern until and unless they are consumed in very large quantities or if there is an already coexisting iodine deficiency.
It is difficult to take in too much iodine from food sources alone. However, very high doses of iodine (pharmacologic) increase stimulation of thyroid gland. This can result in thyroid enlargement (goiter). Excessive iodine intake may also cause hyperthyroidism, symptoms of which include heart rate irregularities, tremor, sweating, palpitations, nervousness and increased activity. Acute iodine poisoning is rare and symptoms include burning of the mouth, throat, and stomach, fever, nausea, vomiting, diarrhea, a weak pulse and coma.
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