Hypothyroidism
Medical Author: Ruchi Mathur, MD, FRCP(C)
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
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Thyroid, Iodine, & Diet: What You Should Know
Medical Author: Ruchi Mathur, MD
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.
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What is hypothyroidism?Hypothyroidism
is a condition characterized by abnormally low thyroid
hormone production. There are many disorders that result in
hypothyroidism. These disorders may directly or indirectly involve the thyroid
gland. Because thyroid hormone affects growth, development, and many cellular processes, inadequate thyroid hormone has widespread consequences for the body. This article will focus specifically on hypothyroidism in adults.
What are thyroid hormones?
Thyroid hormones are produced by the thyroid gland. This gland is located in the lower
part of the neck, below the Adam's apple. The gland wraps around the windpipe
(trachea) and has a shape that is similar to a butterfly - formed by two wings (lobes) and
attached by a middle part (isthmus).
The thyroid gland uses iodine (mostly available from the
diet in foods such as seafood, bread, and salt) to produce thyroid hormones. The two most
important thyroid hormones are thyroxine (T4) and triiodothyronine (T3), which account
for 99% and 1% of thyroid hormones present in the blood respectively.
However, the hormone with the most biological activity is T3. Once released from
the thyroid gland into the blood, a large amount of T4 is converted into T3 -
the active hormone that affects the metabolism of cells.
Thyroid hormone regulation- the chain of command
The thyroid itself is regulated by another gland that is located in
the brain, called the pituitary. In turn, the pituitary is regulated in part by the thyroid
(via a "feedback" effect of thyroid hormone on the pituitary gland) and by another gland called
the hypothalamus.
The hypothalamus releases a hormone called thyrotropin releasing hormone (TRH), which sends a
signal to the pituitary to release thyroid stimulating hormone (TSH). In turn, TSH sends a
signal to the thyroid to release thyroid hormones. If a disruption occurs at any of these
levels, a defect in thyroid hormone production may result in a deficiency of thyroid hormone
(hypothyroidism).
Hypothalamus - TRH
Pituitary- TSH
Thyroid- T4 and T3
The rate of thyroid hormone production is controlled by the pituitary gland. If there is an
insufficient amount of thyroid hormone circulating in the body to allow for normal functioning,
the release of TSH is increased by the pituitary gland in an attempt to stimulate more thyroid
hormone production. In contrast, when there is an excessive amount of circulating thyroid
hormone, TSH levels fall as the pituitary attempts to decrease the production of thyroid hormone.
In persons with hypothyroidism, there is a persistent low level of circulating thyroid
hormones.
Next: What causes hypothyroidism? »
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Hypothyroidism
Thyroid Disease »
Introduction to thyroid disease
When I was asked to write an article on "thyroid disease", I took a very deep
breath. The task seemed daunting. As any Endocrinologist (hormone specialist)
knows, there are many subtopics within this giant topic, and an article like
this could go on for a hundred pages! So, once I caught my breath, I decided to
simply design this article to present a "rough guide" to the thyroid. This
article will be an outline or introduction to many conditions that involve the
thyroid gland. As you read through this, you will find a number of links that
will take you to more in-depth articles dealing with the specific topic in
question.
Thyroid 101: What is the thyroid and what does it do?
The thyroid is a butterfly-shaped gland located in the
front of the neck just
below the Adams apple. The gland wraps around the windpipe (trachea) and has a
shape that is similar to a butterfly ...
Read the Thyroid Disease article »
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