What's Causing My Low Thyroid Level?
Autoimmune disease, surgery, and radiation treatment are possible
reasons why your thyroid gland isn't making enough thyroid hormone to
meet your body's needs. The good news is that whatever the cause,
medicine can get your hypothyroidism under control.
Hashimoto's Thyroiditis
This is the most common reason for low thyroid levels in the U.S. It's
an autoimmune disease, meaning your immune system mistakenly attacks
your body's own healthy cells. In this case, the immune system
destroys the cells needed to make thyroid hormone.
Surgery on the Thyroid Gland
You can get hypothyroidism if you've had surgery to remove part or all
of your thyroid gland. It's sometimes done if you have a growth on
your thyroid or if it's making too much hormone.
Getting the entire thyroid gland removed always leads to
hypothyroidism. For some people, if only part of it is taken out, the
part that's left may still be able to make enough thyroid hormone. But
for others, even partially removing the gland will lead to low thyroid
levels.
Treatment With Radiation
Radiation can damage the cells that make thyroid hormone. You might
get treated with radiation for:
Overactive thyroid gland
Cancer of the head or neck
Hodgkin's disease or lymphoma (cancer of the lymph system)
Thyroid Swelling (Inflammation)
A bacterial or viral infection can make your thyroid gland swell. This
is called thyroiditis. The damaged thyroid leaks its hormone into your
blood, which causes your thyroid hormone level to rise for a short
period of time. Once that hormone has been used up, your thyroid
hormone levels will drop. Low levels from thyroiditis often don't last
long, because your thyroid hasn't been permanently damaged.
Sometimes women get thyroiditis after they give birth, a condition
known as postpartum thyroiditis. It's thought to be an autoimmune
disease, much like Hashimoto's thyroiditis.
Medicines
Some medicines can affect how your thyroid works and lead to low
hormone levels. These include:
Lithium, used for bipolar disorder and depression
Interferon alpha, which treats cancer
Amiodarone (Cordarone, Pacerone), a treatment for heart rhythm problems
Interleukin-2, used for kidney cancer
Too Little or Too Much Iodine
Your thyroid gland needs iodine to make its hormone. You get iodine
from many of the foods you eat. Not getting enough is rare in the
U.S., because it's added to table salt and other foods. The problem is
more common in developing countries.
You can also have a low thyroid level from getting too much iodine.
When there is too much of it in your thyroid, it can block the gland
from making its hormone. It can also lead to an overactive thyroid.
Hypothyroidism at Birth
Sometimes babies are born with a missing or poorly formed thyroid
gland. This is called congenital hypothyroidism.
Damage to the Pituitary Gland
Less often, low thyroid level is caused by a problem outside the
gland. The culprit may be the pituitary gland at the base of the
brain, which directs your thyroid to make its hormone. If the
pituitary gland is damaged from a tumor, surgery, or radiation, it may
not be able to give instructions to the thyroid.
Autoimmune disease, surgery, and radiation treatment are possible
reasons why your thyroid gland isn't making enough thyroid hormone to
meet your body's needs. The good news is that whatever the cause,
medicine can get your hypothyroidism under control.
Hashimoto's Thyroiditis
This is the most common reason for low thyroid levels in the U.S. It's
an autoimmune disease, meaning your immune system mistakenly attacks
your body's own healthy cells. In this case, the immune system
destroys the cells needed to make thyroid hormone.
Surgery on the Thyroid Gland
You can get hypothyroidism if you've had surgery to remove part or all
of your thyroid gland. It's sometimes done if you have a growth on
your thyroid or if it's making too much hormone.
Getting the entire thyroid gland removed always leads to
hypothyroidism. For some people, if only part of it is taken out, the
part that's left may still be able to make enough thyroid hormone. But
for others, even partially removing the gland will lead to low thyroid
levels.
Treatment With Radiation
Radiation can damage the cells that make thyroid hormone. You might
get treated with radiation for:
Overactive thyroid gland
Cancer of the head or neck
Hodgkin's disease or lymphoma (cancer of the lymph system)
Thyroid Swelling (Inflammation)
A bacterial or viral infection can make your thyroid gland swell. This
is called thyroiditis. The damaged thyroid leaks its hormone into your
blood, which causes your thyroid hormone level to rise for a short
period of time. Once that hormone has been used up, your thyroid
hormone levels will drop. Low levels from thyroiditis often don't last
long, because your thyroid hasn't been permanently damaged.
Sometimes women get thyroiditis after they give birth, a condition
known as postpartum thyroiditis. It's thought to be an autoimmune
disease, much like Hashimoto's thyroiditis.
Medicines
Some medicines can affect how your thyroid works and lead to low
hormone levels. These include:
Lithium, used for bipolar disorder and depression
Interferon alpha, which treats cancer
Amiodarone (Cordarone, Pacerone), a treatment for heart rhythm problems
Interleukin-2, used for kidney cancer
Too Little or Too Much Iodine
Your thyroid gland needs iodine to make its hormone. You get iodine
from many of the foods you eat. Not getting enough is rare in the
U.S., because it's added to table salt and other foods. The problem is
more common in developing countries.
You can also have a low thyroid level from getting too much iodine.
When there is too much of it in your thyroid, it can block the gland
from making its hormone. It can also lead to an overactive thyroid.
Hypothyroidism at Birth
Sometimes babies are born with a missing or poorly formed thyroid
gland. This is called congenital hypothyroidism.
Damage to the Pituitary Gland
Less often, low thyroid level is caused by a problem outside the
gland. The culprit may be the pituitary gland at the base of the
brain, which directs your thyroid to make its hormone. If the
pituitary gland is damaged from a tumor, surgery, or radiation, it may
not be able to give instructions to the thyroid.
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