Iodine (I2) is essential in the synthesis of thyroid hormones T4 and T3 and functioning of the thyroid gland. Both T3 and T4 are metabolically active, but T3 is four times more potent than T4. Our body contains 20-30 mg of I2, which is mainly stored in the thyroid gland. Iodine is naturally present in some foods, added to others, and available as a dietary supplement. Serum thyroid stimulating hormone (TSH) level is a sensitive marker of thyroid function. Serum TSH is increased in hypothyroidism as in Hashimoto's thyroiditis. In addition to regulation of thyroid function, TSH promotes thyroid growth. If thyroid hormone synthesis is chronically impaired, TSH stimulation eventually may lead to the development of a goiter. This chapter explores the iodide metabolism and effects of Hashimoto's disease.
TopIntroduction
Thyroid function is controlled by the anterior pituitary gland, which is influenced by the hypothalamus that releases the “thyrotropin releasing hormone” (TRH). The TRH stimulates the pituitary to release the “thyroid-stimulating hormone” (TSH), which causes the thyroid to release the thyroxin (T4) and tri-iodothyronin (T3). If the serum levels of thyroid hormones are high, TSH release is inhibited (feedback mechanism). Iodine is essential in the synthesis of thyroid hormones; T4 and T3 and functioning of the thyroid gland. It plays an important role in preventing breast fibrocystic diseases, cognitive impairment, cretinism, hypothyroidism, hyperthyroidism, and multiple miscarriages.
Sources of Iodine (I2)
Our body contains 20-30 mg of iodine (I2), which is stored in the thyroid gland. Some amounts of iodine are also found in the lactating mammary glands, salivary glands, stomach lining and blood.
Iodine is is naturally present in some foods, added to others, and available as a dietary supplement. Details will be discussed further in chapter 15.
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Foods: Iodine-rich food sources that can help prevent a deficiency include the following: seaweed, cod (a versatile white fish), milk and dairy products, shrimp, Tuna, eggs (mainly egg yolk), dried prunes and plums, and Lima beans (Pennington, 1995; Teas, 2004; Dasgupta, 2008).
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Iodized salt: More than 70 countries, including the United States (US) and Canada, have salt iodization programs. As a result, approximately 70% of house-holds worldwide use iodized salt (World Health Organization, 2007). The US Food and Drug Administration (2009) has approved potassium iodide and cuprous iodide for salt iodization, while the World Health Organization (2007) recommends the use of potassium iodate due to its greater stability, particularly in tropical climates.
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Dietary supplements: Many multi-vitamin/mineral supplements contain iodine in the forms of potassium iodide or sodium iodide. Dietary supplements of iodine or iodine-containing kelp (a type of seaweed) are also available. A small study found that potassium iodide is almost completely (96.4%) absorbed in humans (Aquaron, Delange, Marchal, Lognoné, & Ninane, 2002).