Iodine is categorized as a non-metallic trace mineral. It is needed by the human body in only trace amounts, providing for those vital physiological functions responsible for growth and survival. Iodine occurs naturally in a variety of chemical forms. These forms of iodine are derived from the origin, or source, where a particular food was harvested. For example, the ocean provides for the greatest abundance of iodine, followed by the earth’s top surface layer (soil). The many fruits and vegetables harvested from such iodine rich soils are also abundant in this important mineral.
Iodine is essential in the human diet. It is labeled within the subcategory of micronutrients and is listed as a chemical element (along with oxygen, hydrogen, and iron). Commercially, iodine is typically available in three different forms. These forms are: calcium iodide, potassium iodide, and sodium iodide. Nutritional supplements offer the form of potassium iodide, usually in conjunction with a number of other products. It is estimated that the iodine contained within a dietary supplement accounts for approximately 77% of the total weight of the included potassium iodide. 
This trace mineral is a main component to both our thyroid and parathyroid glands. Iodine is responsible for the regulation of the hormones triodothyronine (T3) and thyroxine (T4) produced by these glands. T4 is the most abundant circulating form of these hormones, and conversion can occur with the assistance of T3 by the enzymes deiodinases. These hormones regulate physiological functions such as gene expression (via DNA and RNA), growth, development, metabolism, and reproductive functioning. [2, 3]
Iodine availability in a particular food is largely dependant upon the content of iodine in either the soil or water in which it was harvested. There are a variety of foods that contain high iodine content, and each are expressed in micrograms (mcg) below. The foods listed below are those sources which yield the highest concentrations of dietary iodine. The expression in micrograms, regarding the amount of iodine contained in one particular food, varies and is directly dependent upon a number of environmental factors. 
|Salt (iodized)||1 gram||77|
|Fish sticks||2 fish sticks||35|
|Tuna, canned in oil||3 ounces, or ½ can||17|
|Milk (cow)||1 cup (8 fluid oz.)||56|
|Egg (boiled)||1 large||29|
|Navy beans||½ cup||35|
|Potato w/peel||1 medium||63|
|Turkey breast||3 ounces||34|
|Seaweed||1 ounce, dried||Variable: approximately 18 micrograms or >|
Iodized table salt(s) usually provides adequate amounts of iodine for those deficient. Certain foods may also block the thyroidal uptake of iodine, called Goitergens. These specific foods have been proven to inhibit iodine absorption of the thyroid: cabbage, broccoli, cauliflower, brussels sprouts, and soybean (isoflavones). 
As previously stated, iodine’s primary function lies within the maintenance and control of hormonal levels in both the thyroid and parathyroid glands.  Unknown to many, the brain (hypothalamus) and pituitary glands are major components in the overall functioning of the thyroid. These two critical body components provide for proper thyroid support by storing iodine and by producing thyrotropin-releasing or thyroid-stimulating hormones (TRH and TSH). These substances are readily available for use in numerous processes throughout the body, including; fat metabolism, energy production, and regulation of cholesterol levels and body temperature.
Clinical research suggests iodine may also play an important role in fibrocystic breast changes, or breast tenderness, prior to menstruation.  Replacement therapies in premenstrual women with deficient levels of iodine during this time period (menstruation), greatly reduced the symptoms associated with fibrocystic breast changes.  Some researchers suggest that iodine supplementation may provide a preventative measure against cancers of the breasts and womb as well.
Also in relation to women, povidone-iodine has been used to treat vaginitis, and is now employed as an alternative therapy. This form of iodine is said to lessen many of the side effects associated with other iodine-containing products, commonly used for the treatment of this condition. Many women suffer from underlying vaginal conditions and are solely dependant upon popular over-the-counter products containing iodine. Although this is a common practice, such products are not always effective. On the other hand, providine-iodine used in douches has shown greater efficacy in clinical study; effectively reducing the occurrence of inflammation associated with vaginitis, as well as the symptoms of tenderness, itching, and vaginal discharge.
The antiseptic properties of Iodine have been well received for centuries. It has been used as a standard topical treatment for various forms of soft tissue traumas (i.e. surface wounds). Iodine is also considered a potent disinfectant, and is added to topical ointments to prevent the spread of various infections.
Iodine may also be equally important in the physical and neurological development of children. Fetal development, particularly of the neurological system, is also dependant upon this trace mineral.
The Food and Nutrition Board (FNB) of the Institute of medicine redefined the recommended dietary intake (RDA) for iodine in 2001; amounts expressed in micrograms below:
|0-6 months||110 (AI)||110 (AI)|
|7-12 months||130 (AI)||130 (AI)|
|19 years & older||150||150||220||290|
These estimates are based upon average individuals with normal thyroid function and are supported by major health agencies, such as: The International Council for Control of Iodine Deficiency Disorders, UNICEF, and the World Health Organization (WHO).
The Food and Nutrition Board of the institute of medicine has also established tolerable upper level (UL) intakes for iodine:
|1-3 years||200 mcg/day|
|4-8 years||300 mcg/day|
|9-13 years||600 mcg/day|
|14-18 years||900 mcg/day|
|19 years and older||1,1000 mcg/day (1.1 mg)|
Referenced in the medical community as “IDDs”, or iodine deficiency disorders, there are many occurrences which signal the onset of an iodine deficiency. The number one sign of an absence, or lowered levels of iodine, in the systems of children, adolescents, and adults, is an enlarged thyroid gland. An enlarged thyroid gland results from the gland trying to become more effective at extracting iodine from the blood to produce the hormones needed for proper bodily functioning. A “goiter” (enlarged thyroid gland) usually forms as a result of deficiency. A “goiter” is usually the first, and most correctable form of an iodine deficiency. Pregnancy and associated fetal development issues are of much greater concern regarding the proper dietary intake of iodine.
Congenital hypothyroidism, also referred to as cretinism, may be considered the most devastating of all known mineral deficiencies. This maternal iodine deficiency results in abnormal brain development, impaired intellectual development, and mental retardation of the unborn child.  In extreme cases, death of the infant will ensue.  Iodine deficiencies account for the number one preventable cause of mental retardation in the world.
Deficiencies in iodine may also result in hypothyroidism (reduction of thyroid hormone synthesis, resulting in lower blood serum levels of iodine), weight gain, lethargy, visual acuity, and hearing. Additionally, one particular study showed a striking parallel between prolonged iodine deficiency and a decrease in the learning abilities of children. 
Toxicities of iodine are possible and have resulted from an individual consuming over several milligrams per day without medical supervision. It is estimated that most people can tolerate at least one milligram (mg) of iodine per day. Acute toxicities usually result from and intake of more than 2 milligrams per day.  Signs and symptoms of an iodine overdose include; acne-like rashes, itching lesions on the skin, gastrointestinal problems, abdominal abnormalities, or hypo/hyper thyroidism (usually caused by a prior underlying thyroid disorder), and even coma.
There have also been studies suggesting a link between excessive intake of iodine and thyroid cancer.  Individuals who have a family history of such diseases (e.g. Graves’ disease or Hashimoto’s thyroiditis), may be more prone to a toxicity of this mineral than an average healthy individual.
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