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Underactive thyroid in U.S. mostly from autoimmune attack
Q. What causes
hypothyroidism? Is it inherited? Is it the result of a nutritional
deficiency?
A. Hypothyroidism is sometimes referred to as "underactive thyroid."
Your thyroid is a small gland at the base of your neck that has a
big impact on how your body works. The hormones your thyroid
produces help regulate your metabolism, including how efficiently
you burn calories and maintain your body temperature and heart rate.
When your thyroid doesn't make enough of two hormones --
triiodothyronine (T-3) and thyroxine (T-4) -- hypothyroidism results
and your metabolism slows. This can lead to sluggishness, weight
gain, dry skin and hair, a hoarse voice and increased sensitivity to
cold. Left untreated, hypothyroidism can lead to potentially serious
complications, including high cholesterol levels and heart disease,
such as congestive heart failure.
The thyroid's production of T-3 and T-4
is governed by two other parts of your body: the pituitary
gland and the hypothalamus. Your pituitary gland is the
master gland that controls all the other glands in your
body's hormone-producing (endocrine) system. Through its
production of thyroid-stimulating hormone (TSH), the
pituitary tells the thyroid how much T-3 and T-4 to make.
One of the jobs of the hypothalamus -- the part of your
brain that controls the entire endocrine system -- is to
signal to the pituitary gland how much TSH to make by
secreting another hormone: thyrotropin-releasing hormone
(TRH).
Although a defect anywhere in the hypothalamus, pituitary or
thyroid can lead to hypothyroidism, most problems that
trigger the condition directly affect the thyroid. It's rare
for a decrease of TSH from the pituitary gland or decreased
secretion of TRH from the hypothalamus to cause
hypothyroidism.
In regard to your question about whether hypothyroidism is
inherited, thyroid disorders do tend to run in families, but
the inherited form of hypothyroidism is rare.
As to nutritional deficiency, a lack of the mineral iodine
can play a part in hypothyroidism. In fact, worldwide, a
lack of iodine is one of the most common causes of the
disease. The body needs iodine to produce T-3 and T-4. In
the United States, however, iodine deficiency is rare,
mainly due to the addition of iodine to table salt.
Hypothyroidism in this country is more commonly caused by
autoimmune thyroiditis (Hashimoto's thyroid disease). In
this disorder, your body's immune system produces antibodies
that attack tissue in the thyroid, affecting the gland's
ability to produce hormones.
Radiation therapy or thyroid surgery for cancer or other
thyroid disease also may decrease thyroid function.
Hypothyroidism can be a side effect of medications such as
thionamides, lithium, amiodarone, interferon-alpha,
interleukin-2 and perchlorate. In some cases, treatment for
hyperthyroidism (overactive thyroid) may reduce thyroid
function too much, and hypothyroidism can result.
In addition, underlying medical conditions also can cause
hypothyroidism. These include the liver disorder
hemochromatosis and sarcoidosis. In some women, pregnancy
triggers an inflammation of the thyroid (postpartum
thyroiditis), which can lead to hypothyroidism.
No matter what the cause, hypothyroidism usually can be
effectively treated by replacing the missing hormone with a
synthetic form of thyroid hormone.
From the MAYO CLINIC |
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