The hormones T3 (triiodothyronine) and T4 (thyroxine) are produced by the thyroid gland. The thyroid gland is located in the lower neck, in front of the windpipe. It is part of the endocrine system, the system that regulates urine production, puberty, growth, energy levels and stress responses in the body. When levels of T3 and T4 are low, the body may be experiencing primary hypothyroidism or central hypothyroidism.
Direct damage to the thyroid gland by tumor, disease, injury or removal can cause the pituitary to under-produce the hormones T3 and T4. T3 and T4 help regulate growth, mental development and metabolism. When it is the pituitary gland itself that is under-producing T3 and T4, the condition is termed primary hypothyroidism. Primary hypothyroidism is most often detected by measuring the levels of TSH in the blood. Higher than normal levels of TSH indicate the thyroid is producing lower than needed levels of T3 and T4.
The thyroid gland is controlled by a gland in the brain called the pituitary. The pituitary gland secretes the hormone THS (thyroid stimulating hormone) in response to the levels of T3 and T4 in the blood system. If problems occur with either the pituitary or the hypothalamus (the other gland in the brain that controls our endocrine system) that cause the pituitary gland to malfunction and not signal the thyroid to produce enough T3 and T4, the condition is called central hypothyroidism. Central hypothyroidism is detected by lower than normal levels of TSH, T3 and T4 in the blood.
Complications Caused by Low Levels of T3 and T4
Because the pituitary and thyroid affect growth and development in puberty, lower levels of T3 and T4 can cause a slower than normal growth rate and delayed puberty, including primary amenorrhoea in women. Other complications include low blood pressure, high cholesterol levels (which can affect heart health), low heart rate and pain in the muscles and joints. Constipation is another unpleasant complication.
Symptoms of Low Levels of T3 and T4
Fatigue is the most commonly reported symptom of low levels of T3 and T4. Sufferers report being tried and listless, even when getting enough sleep and eating well. Unexplained weight gain, cold hands and feet, feeling cold all the time, erratic mood changes, feeling depressed or sad, or having difficulty concentrating for a length of time are also symptoms of low levels of T3 and T4. Dry skin, brittle hair, puffiness of the face or hands or around the eyes are other symptoms.
After taking a patient history and conducting a physical exam, a TSH test may be ordered. If the problem is with hormone levels, a doctor may refer the patient to an endocrinologist. If there are suspected tumors, referral to a surgeon or an oncologist for further evaluation and specific treatment protocols may be made. Primary hypothyroidism is most often treated with a daily thyroid pill. The pill is usually taken for life.