What is the thyroid?
The thyroid is a butterfly-shaped endocrine gland located on the front of the neck below the Adam’s apple. It is controlled by the pituitary gland, a small organ at the base of the brain just above the nasal passages.
Typically, the thyroid remains invisible but can be felt as a soft mass. It varies in size, ranging from 18 to 60 grams in adults.
What are endocrine glands?
Endocrine glands produce and secrete hormones that regulate the activity of cells and multiple organs. Hormones control growth, metabolism and sexual function. As hormones are released into the bloodstream, they act like chemical messengers that communicate information from one group of cells to another.
What is the function of the thyroid?
The primary role of the thyroid is to produce two types of hormones, commonly referred to as T4 (thyroxine) and T3 (triiodothyronine).
Thyroid hormones regulate overall body growth, metabolism and development of the nervous system. They also play an important role in brain growth during fetal development.
Approximately 80 to 90 percent of the hormones secreted from the thyroid gland are T4 hormones; the remaining 10 to 20 percent are T3. However, up to 80 percent of T4 hormones are converted to T3 after they are released into the blood stream.
How does the thyroid work?
The pituitary gland controls the thyroid’s production of T4 and T3 in a thyroid-pituitary negative feedback loop. As thyroid production of T4 and T3 decreases, the pituitary gland secretes a hormone called thyroid-stimulating hormone, which causes the thyroid to produce more hormones.
When thyroid production of T4 and T3 increases, the pituitary gland reduces TSH production. These hormones are in constant communication, but although TSH regulates the thyroid, it doesn’t tell the thyroid how much T4 and T3 to produce and secrete.
Common conditions of the thyroid
Thyroid conditions are common and affect women more than men. The two most common thyroid diseases are hyperthyroidism and hypothyroidism. Others are thyroiditis, thyroid nodules and thyroid cancer.
Hyperthyroidism, or overactive thyroid, is the excessive production of thyroid hormones by the thyroid gland.
Common symptoms include increased heart rate, anxiety, poor sleep, fatigue, muscle weakness, poor heat tolerance, increased metabolism, diarrhea and weight loss despite increased eating. Patients may have a goiter (enlarged thyroid), bulging eyes and hand tremor.
Hyperthyroidism is typically diagnosed with a blood test that reveals high or normal T4 and T3 with a suppressed TSH level.
The three treatment options include radioactive iodine, anti-thyroid medication to control thyroid function and, occasionally, surgery to remove the thyroid.
With hypothyroidism, or underactive thyroid, the thyroid gland does not produce enough thyroid hormones.
Common symptoms include lowered metabolism, decreased heart rate, weight gain, lack of energy, poor tolerance of cold, dry skin and depression.
Hypothyroidism affects women to men at a 2-to-1 ratio. It causes menstrual irregularity, impaired fertility and increased risk of miscarriage.
Diagnosis is relatively simple and consists of a blood test that shows an elevated TSH with low thyroid hormones. The TSH is high because it functions like a thermostat that keeps trying to stimulate without effect.
According to Francesco S. Celi, MD, chair of the Division of Endocrinology and Metabolism at VCU School of Medicine, hypothyroidism is typically treated with replacement hormones. Treatment includes generic T4 hormones (for example, levothyroxine) or a combination of T3 and T4.
Patients are advised to have blood work done every four to six weeks while the dosage is being adjusted. Once it is set, it does not change.
“Symptoms of hyperthyroidism or hypothyroidism should be assessed by either a primary care physician or an endocrinologist,” says Dr. Celi.
Thyroiditis, or inflammation of the thyroid, can be chronic or acute, depending on the cause. The common form is Hashimoto’s thyroiditis, which is a frequent cause of hypothyroidism.
Patients with Hashimoto’s thyroiditis usually show no symptoms until they develop hypothyroidism. In cases of acute thyroiditis, patients can have neck pain with symptoms similar to either hyperthyroidism or hypothyroidism.
Although there is no cure for Hashimoto’s, hormone replacement with medication can regulate hormone levels and restore normal metabolism.
Thyroid nodules are growths within the thyroid. They are very common in the elderly and can cause anxiety when discovered. Most are benign, cause no symptoms and are found when medical professionals are looking for something else.
For benign nodules without symptoms, treatment is not required; regular ultrasound monitoring is usually adequate. Surgical removal of tissue could be in order for nodules causing symptoms or if malignancy is a concern.
Thyroid cancer is three times more common in women than in men. Most thyroid cancers demonstrate slow growth with no symptoms.
The most effective management for thyroid cancer is surgical removal of the thyroid followed by radioactive iodine ablation — where radioactive iodine is administered to destroy residual healthy thyroid tissue remaining after the thyroidectomy — and TSH suppression therapy.
Common myths about the thyroid
The most common misnomer about the thyroid is that it increases energy and helps people lose weight.
Many people believe being chronically tired or unable to lose weight indicates their thyroid function must be low and a thyroid supplement would help. But many people with normal thyroid function experience these symptoms. Blood work is necessary to determine if a patient’s thyroid is underactive.
While numerous thyroid supplement or remedy products are available in the marketplace, patients are advised to consult their physicians before taking any of them. Patients with normal thyroid function should work with their doctors to find the real causes of their symptoms.
There is not much one can do to maintain or improve thyroid health.
The thyroid requires iodine to make thyroid hormones. In the past, iodine deficiency was common in noncoastal areas where seafood was in short supply. Today however, iodine deficiency is less common because it is in most foods via salt.
The recommended dietary allowance for iodine in adults is 150 micrograms per day. One teaspoon of iodized salt contains approximately 400 micrograms of iodine.
“Adequate iodine intake in the diet is necessary for the prevention of goiter,” says Dr. Celi. “But severe iodine deficiency is very rare in the United States.”