The thyroid gland is the biggest
gland in the neck. It is situated in the front of the neck, just below
your Adam’s apple, on either side of the neck, and partly wraps around
the trachea (wind pipe). The sole function of the thyroid is to make
thyroid hormone. This hormone has an effect on nearly all tissues of
the body where it increases cellular activity. The function of the
thyroid therefore is to regulate the body's metabolism.
thyroid gland receives much if its instruction from the pituitary
gland, a small gland located at the base of brain. The pituitary gland
secretes Thyroid Stimulating Hormone (TSH). TSH, as its name implies,
stimulates the thyroid gland to start producing thyroid hormone. When
the thyroid gland starts to slow down or become underactive, it doesn’t
use up all the TSH being released by the pituitary, and the TSH levels
start to rise.
TSH blood levels are commonly measured as a
way to screen for thyroid abnormalities. The normal range for most labs
is 0.5 – 5.5. The higher the number, the greater the indication of
underactive thyroid. At Valley Sports Physicians, we prefer to see
people in the “optimum” range, under 2.0.
main hormone produced by the thyroid gland is T4, also known as
levothyroxine. It is a molecule that contains 4 iodine units (hence the
“T4”). The T4 gets secreted by the thyroid gland and enters the blood
stream. Once it reaches the body, T4 gets converted to T3
(tri-iodothyronine) by cleaving off 1 iodine unit. (A small amount of
T3 is also produced directly in the body.) T3 is 4-5 times more active
or powerful than T4 and is the real thyroid hormone.
thyroid gland is underactive (hypothyroidism), insufficient amounts of
T4 are produced, resulting in too little T3. On the other hand, your
body may also not adequately convert T4 to T3, in spite of adequate T4
There are several blood tests to measure T3 and T4
levels. At Valley Sports Physicians, we find the most useful tests to
be the Free T3 and Free T4 levels. These test measure the amount of T3
and T4 that is “free” in the blood to be used by the body. We maintain
that optimum levels of T3 should be over 4 pg/ml (the normal range is
The most common thyroid medications for treating
hypothyroidism include Synthroid® and Levoxyl®, brand names for
levothyroxine (T4). Armour Thyroid® is also used; this is a combination
of T4 and T3. It is a natural product derived from pig thyroid. A
synthetic form is also available known as Thyrolar®. We prefer that
brand names be requested, in order to insure consistent quality and
bioavailability. The added cost is minimal.
Thyroid blood tests should be repeated in about 6 weeks after either starting treatment or changing doses.
For more information, go to www.endocrineweb.com/thyfunction.html.