DOCTOR'S VIEW ARCHIVE

Thyroid & Iodine..What You Should Know-Part 1

Medical Author: Ruchi Mathur, M.D.
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

Many of my patients ask questions or make comments about iodine use in thyroid disease. Examples are: " Should I increase the iodine in my diet if I'm hypothyroid?" "My mother had hyperthyroidism, and they told her it was because of a lack of iodine." " My sister has thyroid disease, and to avoid getting it, I'm taking Kelp tablets." "Can I eat sushi if I take Synthroid?"

Although these questions and comments are relevant, this subject is peppered with "old wives tales" and folklore. In the first part of this discussion, I'd like to focus on the role iodine in relation to the thyroid gland and its function.... a bit of physiology for the beginner. Later, I will discuss how an excess or deficiency of iodine can contribute to diseases of the thyroid gland.

Why does the body need iodine?

The major function of the thyroid gland is to produce thyroid hormone in an amount sufficient to meet the body's needs. To make thyroid hormone, the thyroid uses iodine. If iodine is not available in the diet, the thyroid may produce an insufficient amount of hormone.

How much iodine does the body need?

Areas in the United States where iodine deficiency occurs are scarce. In North America, iodine is added to salt and bread. It is also present in additives, water sources, medications, and dietary supplements. The daily iodine intake varies widely throughout the world. A minimum of 60 micrograms of elemental iodine per day is required to make thyroid hormone. The following lists examples of average iodine intake in various countries and the recommended amount of iodine consumption:

Typical Iodine Intakes

North America

200-700 micrograms/day

Germany

20-150 micrograms/day

Chile

50-150 micrograms/day

Switzerland

130-180 micrograms/day

Recommended Daily Intake

Adults 150 micrograms/day
Children 90-120 micrograms/day
Pregnant Women 200 micrograms/day

In North America, the higher values are mainly due to an increased intake in salt. In Japan, where foods rich in iodine are consumed regularly, the intake may be as high as over 1000 micrograms/day. Although iodine consumption is generally lower in Europe, the people in these countries do not usually develop thyroid disease. However, when they are exposed to unaccustomed, large amounts of iodine (such as moving to North America and increasing their iodine intake), they can develop thyroid disease. This occurs particularly in people who have an underlying predisposition to developing thyroid disease.

How is iodine used by the thyroid?

The process by which the thyroid uses iodine is actually quite complicated and certain steps are still unclear. Essentially, iodine is converted to its free elemental form, called iodide. Iodide enters the thyroid gland through a special transport mechanism. Iodide then undergoes a process called oxidation and is incorporated into intermediate hormones called MIT (Monoiodotyrosine, which contains 1 iodide) and DIT (Diiodotyrosine, which contains 2 iodides.) These compounds then combine to form the active hormones, tri-iodothyronine (T3) and thyroxine (T4). T3 is the most biologically active thyroid hormone. It is formed by combining a MIT with a DIT (so the total of iodides in the molecule is 3). T4 is formed in much greater quantity by combining a DIT with another DIT (so that the total of iodides in the molecule is 4). These hormones are then stored in the thyroid gland and released into the blood stream.

Based on the above summary, it is evident that thyroid hormone is actually made up of iodide/iodine directly. So you can see the importance of iodine in relation to the function of the thyroid gland. Whew! Glad the physiology stuff is over!!

I hope the above information helps to provide a basic understand of why iodine is important, how much iodine is needed, and how it is used by the thyroid gland. With this background, we can now continue on to part 2, which will address specific problems if too much or too little iodine intake occurs. Stay tuned!

For Part Two of this series, please see Thyroid & Iodine - Part II.


Last Editorial Review: 10/23/2006