Hypothyroidism is a thyroid disease that affects people globally. Two- to three-percent of Americans have hypothyroidism; 10-15% mild hypothyroidism. Hypothyroidism affects women more than men. The thyroid gland is located in the neck and secretes hormones into the blood, which are then carried into the body’s tissues. The thyroid gland mainly produces a hormone called thyroxine (T4), which is then converted by each of the body’s organs to the active form triiodothyronine (T3). They both work to keep the body’s organs functioning properly. Thyroid hormone is important for regulation of body temperature, heart rate, blood pressure, and metabolism.
Hypothyroidism is a disease where the person affected has an under-functioning thyroid. When you have hypothyroidism, certain body functions slow down and may lead to fatigue, dry skin, and memory problems. Hypothyroidism is diagnosed with a blood test. You may experience a variety of symptoms—some resembling other health issues. Some symptoms you might be aware of and some you may not notice at all.
The most common and noticeable symptoms may include:
Some symptoms are considered severe, although the ranges of severity differ from person to person. The symptoms listed below can be caused by hypothyroidism and may affect other health problems (eg, worsen a condition).
More severe symptoms associated with hypothyroidism may include:
Hypothyroidism, an under-performing thyroid, may have many different causes—and some are more prevalent than others. The most common cause of hypothyroidism is an autoimmune disease.
About Autoimmune Disease
Our bodies’ immune systems are charged with protecting us from bacterial and viral invaders. The immune system attacks invaders (eg, cells). People with autoimmune hypothyroidism are at a disadvantage because their immune system attacks the normal thyroid gland. These attacks cause the thyroid hormone producing cells to malfunction, and inhibit the thyroid gland’s ability to synthesize thyroid hormone. Eventually, there are not enough cells left to meet the body’s need for thyroid hormone. This is more common in women than men—and can begin at any point in a person’s life, but tends to become more common as people age.
The most prevalent type of autoimmune hypothyroidism is a disease that causes the thyroid to shrink—it is called Hashimoto’s disease and may cause Hashimoto’s thyroiditis.
Thyroiditis means that the thyroid gland is inflamed. In addition to Hashimoto’s disease, viral infections can occasionally cause thyroiditis. In the case of a viral infection, the thyroid gland may release its entire supply of stored thyroid hormone at once into the blood. In turn, this causes the thyroid to become over-active (or, hyperthyroidism) for a short amount of time. After all the thyroid hormone is released, then the thyroid becomes underactive. Fortunately, about 75% of patients who suffer from viral thyroiditis regain proper thyroid function. Approximately 25%, however, are left with permanent hypothyroidism.
There are several other causes of hypothyroidism that are less common than autoimmune-related disorders, but still somewhat prevalent.
Partial or Complete Removal of the Thyroid
When a portion of the thyroid gland is surgically removed (eg, patients with thyroid nodules, thyroid cancer, Graves’ disease), this causes the remaining thyroid tissue to stop working properly—and may result in hypothyroidism. In some cases, such as patients with thyroid nodules, thyroid cancer, or Graves’ disease, the entire thyroid may even require removal.
Some patients undergo radiative iodine therapy as part of treatment for thyroid cancer, Graves’ disease, or a nodular goiter. Radioactive iodine destroys the thyroid tissue resulting in hypothyroidism. Some diseases treated using radioactive iodine lead to hypothyroidism (eg, Hodgkin's disease or lymphoma, cancers of the head and neck).
Congenital Problems: Born Without a Thyroid Gland
Some babies are born without a thyroid or the thyroid is malformed (about 1 in 4,000 babies each year). A smaller number of babies are born with the thyroid intact, but in the wrong place. When the thyroid is in the wrong place, it is called an ectopic thyroid. In some patients with an ectopic thyroid gland, the thyroid cells or enzymes malfunction.
Furthermore, there are other cases where the thyroid works properly for months or years, but stops functioning later in the child’s life. The United States tests all children at birth for hypothyroidism.
Medication-related Causes of Hypothyroidism
Additionally, there are certain medications that can cause a thyroid to lose its ability to produce thyroid hormone. Medications that trigger hypothyroidism onset include lithium, amiodarone, interferon- alpha, interleukin-2, and some medications used to treat cancers.
Iodine levels can also affect thyroid hormone production. The thyroid needs iodine to make thyroid hormone. An imbalance in iodine—too much or too little—can cause or make hypothyroidism worse. Iodine comes into the body, mostly via diet, such as dairy, chicken, beef, pork, fish, and iodized salt.
In the United States, iodine deficiency is a rare cause of hypothyroidism due to supplementation of salt with iodine. The most common reason a person can have a high iodine level is due to the use of dietary supplements containing kelp. These supplements may be marketed for weight loss.
Pituitary Gland Dysfunction
The pituitary gland works together with the thyroid gland. The pituitary gland tells the thyroid how much thyroid hormone to produce via a hormone called thyroid stimulating hormone (TSH). If the pituitary gland doesn’t produce TSH properly (eg, due to injury, radiation, tumor, surgery), the thyroid gland may not produce thyroid hormone adequately.
American Thyroid Association. Hypothyroidism. A Booklet for Patients and Their Families. 2013.