Hypothyroidism is a health condition in which the thyroid gland does not produce sufficient amounts of thyroid hormones (thyroxine (T4) and triiodothyronine (T3)). Hypothyroidism is associated with a decreased metabolic rate. More than 5 million Americans suffer from hypothyroidism, and many of them don't even realize it. The thyroid gland can be found just below the larynx, in front of and to either side of the trachea (windpipe).
Historically, iodine deficiency was the main cause for hypothyroidism. The thyroid gland is the only tissue in our body that can absorb iodine and iodine is essential for thyroid hormone production. We mostly get our iodine through iodized table salt, but if a person's diet lacks sufficient iodine, hypothyroidism may develop.
Because thyroid hormones regulate every cell's metabolism, thyroid hormones are essential for all tissues in the body. If thyroid output is insufficient, more thyroid stimulating hormone (TSH) is being produced by the pituitary gland (a small sized gland in the middle of the brain just below the hypothalamus). Continued stimulation of the thyroid gland could result in a greatly enlarged thyroid, called a thyroid goiter.
Hypothyroidism is frequently caused by thyroiditis, an inflammation of the thyroid gland. This is usually an auto immune reaction, whereby the patient's own immune system attacks the thyroid. This condition occurs in about 5% of women after giving birth. This form of post-partum thyroiditis first causes hyperthyroidism, an increased output of the thyroid gland. However, sometimes part of the thyroid is being destroyed by either thyroiditis or by treatments that keep in check the overactive thyroid, which can result in lifelong hypothyroidism.
Hypothyroidism can also be caused when the pituitary gland produces an insufficient amount of thyroid stimulating hormone (TSH) to induce the thyroid to create more thyroid hormones. This condition is often caused by damage to the pituitary, either by a tumor, surgery or radiation. Even more rare is the condition in which the hypothalamus does not produce enough thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to create TSH.
What are the symptoms of hypothyroidism?
- inability to lose weight despite dieting
- increased sleepiness
- increased sensitivity to cold temperatures
- muscle cramps and joint pain
- water retention
- dry itchy skin
- brittle hair and fingernails
- decreased heart output
- disturbed menstrual cycle (late symptom)
- arteriosclerosis (late symptom): lack of thyroid hormones raises the level of blood lipids including cholesterol, which is associated with increased risk for atherosclerosis and arteriosclerosis
- sluggish speech with a hoarse sounding voice (late symptom)
Hypothyroidism in children will result in slowed growth and delayed development.
How is hypothyroidism diagnosed?
Doctors often look at the levels of TSH (produced by the pituitary) and both free and total thyroid hormones T3 and T4. Additional diagnostic tests include a 24 hour urine T3 test, serum cholesterol test, antithyroid antibody test and a test for anemia.
Treatment options for hypothyroidism
Thyroid hormone has a long half-life (close to a month), so it is relatively easy to maintain a steady level of thyroid hormone activity in the body by taking a tablet of synthetic thyroxine or thyroid extract (usually from pig). A thyroid supplement that supports healthy thyroid functioning may also be considered. In addition, foods that contain anti-thyroid substances (leading to TSH-stimulated enlargement of the thyroid) should be limited or avoided. Such anti-thyroid substances are found in some varieties of turnips and cabbages.