Iodine

You are probably familiar with iodine if you have ever backpacked in the mountains and used iodine tablets to purify your drinking water or if youve ever cleaned a minor skin wound with an iodine-based disinfectant. Yet, iodines spectrum of importance extends much farther, being an essential mineral for physiological functioning and for life.

Iodine is a trace mineral that is required by the body so that it can synthesize the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). These two hormones are related in that T4 contains four iodine atoms and when one of these atoms is stripped off, it becomes T3, with three iodine atoms remaining.

The body contains approximately 20 to 30 milligrams of iodine under normal circumstances. Most of this iodine is stored in the thyroid gland, located at the front of the next, just under the voice box. Iodine in smaller amounts is also found in the stomach lining, salivary glands, lactating mammary glands and in the blood.

Physiological functions of iodine

• Helps ensure proper thyroid gland functioning

Physiological events that may signal a need for greater intake of iodine

• Goiter (enlargement of the thyroid gland)
• Fatigue
• Weakness
• Depression
• Weight gain

Functions of iodine

Regulating thyroid hormones

Iodine is essential to human life since it is a component of the thyroid hormones T4 (thyroxine) and T3 (triiodothyronine). If the body does not have an adequate supply of iodine, it is unable to synthesize these hormones. These hormones are of utmost important, and therefore by extension so is iodine, since these hormones regulate metabolic function in every body cell and play a role in virtually every physiological function. Therefore, an iodine deficiency can have a devastating impact on health and well-being.

Thyroid hormone synthesis is tightly regulated. When levels of thyroid hormones in the blood drops, the pituitary gland secretes thyroid-stimulating hormone (TSH), which, as its name suggests, stimulates the thyroid gland to increase its uptake of iodine from the blood in order that more thyroxine (T4) can be manufactured. As necessary, T4 is converted to the T3, the metabolically active hormone form. This process involves removing an iodine atom from T4.

Other functions of iodine

In addition to regulating thyroid hormones, iodine may serve other physiological functions. It may help to inactivate bacteria which supports its role in water purification and as a skin disinfectant. It may also play a role in preventing fibrocystic breast disease, a condition characterized by painful and swollen breasts, by regulating the effect of estrogen on breast tissue. Additionally, some researchers have also suggested that iodine deficiency impairs immune system function and that adequate iodine status is necessary to prevent miscarriages.

Causes and symptoms of iodine deficiency

Iodine deficiency was quite common in the United States and Canada up until the early part of the 20th century. With the generalized use of iodized salt in these countries, as well as the fact that iodine content of many commonly consumed foods in North America (such as cow\'s milk) has increased secondary to addition of iodine to animal feed, this problem has been almost completely resolved. Unfortunately iodine deficiency is a still a significant problem in countries where iodized salt is not commonly consumed.

Iodine deficiency can be caused by the overconsumption of certain foods, called goitrogens that block the absorption and utilization of this mineral. Goitrogens are found in cruciferous vegetables, soy products, millet, cassava root and mustard. Additionally, goitrogenic substances may be found in drinking water from contaminated wells.

Deficiency of this vital mineral results in the reduced synthesis of thyroid hormone. As the body attempts to produce thyroid hormones in spite of sufficient iodine availability, the thyroid gland is overstimulated by thyroid stimulating hormone (TSH). This results in enlargement of the thyroid gland, goiter, one of the earliest symptom of iodine deficiency.

Iodine deficiency can manifest as either hypothyroidism or hyperthyroidism. The former is characterized by symptoms including depression, fatigue, weakness and/or weight gain while the latter condition includes a constellation of symptoms including rapid heart beat, fluctuations in appetite and weight loss.

If severe iodine deficiency manifests during pregnancy or infancy, it can cause cretinism. This condition is distinguished by hypothyroidism leading to failure of the thyroid. It can also result in severe mental retardation, stunted physical growth, spasticity and deafness. Cretinism can be corrected with iodine supplementation if discovered in its initial stages.

Causes and symptoms of iodine toxicity

Toxicity can occur with accidental overdose of iodine from supplements or medications in amounts exceeding one gram. Symptoms include abdominal pain, nausea, vomiting, diarrhea, weak pulse, coma and burning in the mouth, throat and stomach.

In general, it is difficult to attain excessive amounts of iodine from food sources alone and even high intakes are well-tolerated by most people. Yet, in select circumstances, too much iodine can actually cause adverse events including the inhibition of thyroid hormone leading to goiter development and hypothyroidism. Additionally, it can cause hyperthyroidism, thyroid papillary cancer and/or iodermia, which is a serious skin reaction.

Individuals who have an autoimmune thyroid disease, such as Graves disease or Hashimotos disease, or who have experienced an iodine deficiency at some point in their life, may be more susceptible to the dangers of excessive iodine consumption. These individuals may need to monitor their iodine intake more carefully.

In consideration of the potential for toxicity, in 2001 the Institute of Medicine at the National Academy of Sciences set the following Tolerable Upper Intake Levels (UL) for iodine:

• children, 1-3 years: 900 micrograms for children
• children, 4-8 years: 300 micrograms for children
• children 9-13 years: 600 micrograms for children
• teenagers 14-18 including pregnant and lactating women: 900 micrograms
• adults over 19 years including pregnant and lactating women: 1,100

Effects of cooking, storage and processing on iodine

Common food processing techniques increase the amount of iodine in foods. Potassium iodide is added to table salt to produce iodized salt, which has greatly increased the iodine intake of individuals in developed nations. Adding iodine-based dough conditioners, a common practice in commercial bread-making, results in increase iodine content of bread.

Interactions between medications and iodine

The following medications affect iodine status:

• Amiodarone (commonly sold under brand name Cordarone)
  • contains iodine and can disrupt proper thyroid function
• Medications and foods containing the red food coloring agent Erythrosine
  • Contains iodine and can disrupt proper thyroid function

Interactions that occur between iodine and other nutrients

Selenium is required to remove an iodine molecule in the conversion of thyroxine (T4) to triiodthyronine (T3). The iodine molecule that is removed from T4 returns to the bodys iodine pool to be reused to make additional thyroid hormones. Deficient selenium slows T4 to T3 conversion and reduces the availability of free iodine for the manufacture of new thyroid hormones.

Deficiency of several nutrients including vitamin A, vitamin E, zinc and iron makes the effects of iodine deficiency more apparent. Results from animal studies suggest that arsenic interferes with the thyroids uptake of iodine, a consequence that can lead to goiter

Health conditions that require special emphasis on iodine

Individuals who have the following health conditions should pay special attention to their iodine status:

• Cognitive impairment
• Cretinism
• Fibrocystic breast disease
• Goiter
• Hyperthyroidism
• Hypothyroidism
• Multiple miscarriages

Forms in which iodine is found in dietary supplements.

Iodine may be found in dietary supplements. complexed either with potassium (potassium iodide) or sodium (sodium iodide). Additionally the elemental form of iodine, iodine caseinate, is also available. Kelp-containing products are often used as a source of supplemental iodine.

Foods that are concentrated forms of iodine

Most natural foods typically contain a very small amount of iodine with levels varying depending upon environmental factors such as soil iodine concentration and use of fertilizers. Processed foods that contain iodized salt and breads that contain iodate dough conditioners are among the richest food sources of iodine.

Regarding natural foods, cows milk, eggs and strawberries are very good sources of iodine while cantaloupe and mozzarella cheese are good sources. Seafoods and sea vegetables, notably kelp, provide dietary sources of iodine.