The thyroid gland is an important endocrine gland that controls the body’s metabolism. It is a small butterfly-shaped gland located in the front of the neck just below the Adam’s apple. The thyroid gland produces the hormones tetraiodothyronine (T4) and triiodothyronine (T3).
Together these hormones regulate how your cells use energy. The pathways by which cells use energy is called metabolism. Your body’s general metabolism determines blood pressure, heart rate, and weight.
Hypothyroidism is a condition where your thyroid gland does not make enough thyroid hormone. Low levels of thyroid hormone interfere with the body’s ability to perform normal metabolic functions such as efficient use of energy from food products, regulation of many chemical reactions in the body, and maintenance of healthy cells, bones and muscles, to name a few.
There is no known prevention for hypothyroidism, nor is there a cure. Once you have it, you have it for life.
The most common causes are surgical removal of your thyroid, autoimmune diseases, and radiation treatment.
This may be necessary to treat hyperthyroidism, or tumors of the thyroid gland. Hypothyroidism will occur when the entire gland is removed.
These diseases cause the production of antibodies that attack your thyroid gland. Autoimmune thyroiditis, which can appear suddenly or develop over several years, is more common in women. Hashimoto’s thyroiditis and atrophic thyroiditis are the most common types.
Radiation treatment for Hodgkin lymphoma and cancers of the head and neck can injure the thyroid gland. If this occurs, the gland cannot produce enough thyroid hormone to keep your metabolism running smoothly. Radioactive iodine (I-131) destroys the thyroid gland and can be used to treat people with Grave’s disease and thyroid cancer. Grave’s disease is an autoimmune disease that causes hyperthyroidism.
Some children are born without a thyroid gland or they may have one that doesn’t function properly.
Viral or Autoimmune Thyroiditis
When antibodies or viruses attack your thyroid, thyroid hormones can leak out. Sometimes all of the thyroid’s hormones are released into your blood at one time. When this happens, symptoms of thyroid excess or hyperthyroidism occur.
Lithium (used to treat bipolar disease), amiodarone (medication with high iodine content used to treat serious ventricular arrhythmias, interleukin 2 (anti-viral and anti-cancer agent), and interferon alpha (anti-viral agent) are medications that can cause hypothyroidism. This is more likely to occur in people who have a genetic tendency for autoimmune thyroid disease.
The pituitary is the master gland that signals the thyroid how much hormone it needs to produce. If the pituitary is damaged by trauma, stroke, or tumor, the signal to release thyroxine can stop. This causes the thyroid to stop making thyroid hormone.
Not Enough or Too Much Iodine
The thyroid gland needs iodine to make T3 and T4. Iodine had to be obtained in the diet. Too little iodine can cause hypothyroidism and, ironically, too much iodine can
block the thyroid’s ability to make thyroid hormone.
Diseases like amyloidosis can cause the thyroid to become overwhelmed by abnormal proteins where the cells cannot function normally.
The following groups are at a greater risk for developing hypothyroidism:
- women over age 50.
- people with autoimmune diseases or a parent or grandparent with an autoimmune disease.
- people given radioactive iodine or radiation therapy
- people treated with antithyroid medication
- those with a history of radiation to the neck and upper chest people with a partial thyroidectomy (removal of the thyroid)
- post-partum females
There are no symptoms that are unique to hypothyroidism. There may be no symptoms early in the disease process. Long standing, untreated hypothyroidism can cause obesity, joint pain, heart disease, and infertility. Other symptoms can include:
- increased sensitivity to cold
- heavier menstrual flow
- brittle hair and nails
If left untreated, the following symptoms can occur:
- puffiness of the face, hands, and feet
- slowed speech
- decreased taste and smell
- thin eyebrows
- thickened skin
- coma (called “myxedema coma”)
Your doctor first conducts a physical exam and reviews of your medical history. This can reveal any procedures like thyroid surgery or radiation treatments connected to hypothyroidism. Family history might reveal a close relative with autoimmune disease. Medication history might be positive for drugs, such as lithium and amiodarone that can cause the condition.
Because hypothyroidism is most often found in women over age 50, some doctors advocate thyroid function screening for this group. Doctors also may suggest screening women of childbearing age.
Blood tests also are common. These include:
- thyroid function tests: T4, T3RU and TSH
- tests for pituitary function: TSH
- cholesterol (can be elevated)
- CBC (may show anemia)
- liver enzymes (can be elevated)
- prolactin (can be elevated)
- electrolytes (sodium can be low)
In hypothyroidism, T4 is low and TSH is high. This means the pituitary is sending more TSH to stimulate the thyroid, but the thyroid does not respond. A low TSH indicates the pituitary may be the cause of hypothyroidism.
A common treatment is to replace thyroxine with a specific synthetic thyroid hormone (levothyroxine). This hormone is safe and affordable, but determining the right dosage often takes time. Your metabolic rate has to be returned to normal. Raising it too quickly can cause palpitations and make some medical problems like coronary artery disease and atrial fibrillation worse. Symptoms of thyroid hormone excess are:
- shakiness or tremors
- increased appetite
Diets rich in soy and high fiber can interfere with levothyroxine absorption. Medications and supplements also can reduce absorption. These include:
- calcium supplements
- iron supplements
- aluminum hydroxide (present in some antacids)
Written by: Verneda Lights and Matthew Solan
Published on Aug 07, 2012
Medically reviewed by Brenda B. Spriggs, MD, MPH, FACP