The thyroid, a gland located in the neck, is responsible for secreting two hormones, thyroxine (T4) and triiodothyronine (T3), important in regulating many cellular functions in the body. When the levels of hormones are too low, the condition is known as hypothyroidism. This condition can be initiated from within the thyroid, referred to as primary hypothyroidism, or by a dysfunction of the pituitary gland, called secondary hypothyroidism. Approximately 95 percent of all hypothyroid cases are primary hypothyroidism, according to the University of Maryland Medical Center, and may be caused by several conditions.
Hashimoto's Thyroiditis
Hashimoto's thyroiditis, a genetic disease, is the most common cause of hypothyroidism in the United States, according to doctors at the Mayo Clinic. Hashimoto's thyroiditis is an autoimmune disease, meaning the cells of the immune system mistakenly attack cells in the body. In this case, the cells of the thyroid gland are under attack. This triggers inflammation of the thyroid, resulting in a goiter, a mass or cyst, in the neck.
The inflammation caused by Hashimoto's thyroiditis damages the cells of the thyroid, inhibiting them from producing the thyroid hormones. This disease is a life-long disease and requires continued treatment with synthetic thyroid hormones.
Overtreatment of Hyperthyroidism
Hyperthyroidism, which is caused by an overactive thyroid producing too much thyroid hormones, affects approximately 1 percent of the people in the United States, as reported by the National Endocrine and Metabolic Diseases Information Service. Hyperthyroidism is often treated with antithyroid medications, which inhibit the production of thyroid hormones. These medications, such as methimazole and propylthiouracil, inhibit the thyroid from utilizing iodine to produce thyroid hormones. When these drugs are taken for too long or in too high a dosage, the result can be hypothyroidism.
Pregnancy
During pregnancy, many women will develop antibodies, proteins produced by the immune system, to the cells of their thyroids. This can cause inflammation of the thyroid and interfere with the production of thyroid hormones, resulting in hypothyroidism.
Radiation Therapy
Patients suffering from cancer may receive radiation treatments. Radiation treatments utilize energy, called ionizing radiation, to kill cancer cells. Radiation is administered locally, meaning to the specific area of the body where the cancer is located. When delivered to the neck, radiation can damage the cells of the thyroid gland. This damage can cause thyroid hormone production to decrease, resulting in hypothyroidism.
Iodine Deficiency
The thyroid cells use iodine, which is ingested with many foods, to make thyroid hormones. In fact, the thyroid cells are the only cells in the body able to absorb iodine, according to EndocrineWeb.com. The cells in the thyroid combine the iodine with a specific amino acid, called tyrosine, to produce T3 and T4. When there is not enough iodine, production of T3 and T4 decreases, resulting in hypothyroidism.
