The month of January is dedicated to raising awareness about thyroid disease. According to the American Thyroid Association, over 12% of Americans (20 million) will develop a thyroid condition. Thyroid disease affects women more often than men, and up to 60% of people with thyroid disease are unaware that they have a health problem.
The Role of the Thyroid Gland
The thyroid gland is a butterfly-shaped endocrine gland located in the lower front of the neck, in front of the windpipe, just below the Adam’s apple and above the collarbones. The thyroid gland secretes hormones that regulate metabolism—the process of converting nutrients in food into energy. This process generates heat and energy for all the organs in the body.
Thyroid hormone is vital to normal brain development, digestion, muscle control, and energy and mood regulation. Iodine, a mineral found in iodized table salt, seafood, bread, and milk, is required by the thyroid gland to produce thyroid hormone.
The thyroid gland extracts iodine from the blood and uses it to produce two types of thyroid hormone:
- Tetraiodothyronine or Thyroxine (T4)
- Triiodothyronine (T3)
The thyroid gland stores thyroid hormone and releases it when the body demands more. Once it is released from the thyroid gland, it travels through the blood bound to proteins and binds to receptors on the surface of cells.
Regulating Thyroid Hormone Production
At the base of the brain sits the pituitary gland. This “master gland” regulates many other endocrine glands. The pituitary gland releases a messenger called thyroid-stimulating hormone, which travels through the blood to the thyroid gland and increases T4 and T3 production. When T4 and T3 levels rise, they exert negative feedback on the pituitary gland and a part of the brain called the hypothalamus. This feedback loop ensures that a healthy thyroid gland produces the exact amount of T4 and T3 thyroid hormones required to meet the body’s needs.
What Are the Early Warning Signs of Thyroid Disease?
Thyroid disease symptoms vary depending on whether the thyroid gland produces too much or too little thyroid hormone, both of which can cause health problems.
Hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormone. Symptoms of hypothyroidism include:
- Excessive fatigue
- Cold intolerance
- Unexplained weight gain
- Dry skin
- Hair loss
- Slow heart rate
- Puffy face
- Muscle fatigue
- Cognitive issues
Hyperthyroidism is a condition in which the thyroid gland produces too much thyroid hormone. Symptoms of hyperthyroidism include:
- Anxiety, nervousness, or irritability
- Heat intolerance
- Racing pulse
- Trouble sleeping
- Weight loss even with proper nutrition
- Fine tremors
- Palm redness
- Swollen or bulging eyes (Grave’s disease)
The symptoms of too little thyroid hormone are the opposite of too much thyroid hormone.
Who Is at Increased Risk for Thyroid Disease?
Increased age is a risk factor for thyroid disease, particularly in men over the age of 60 and women over 50. Other risk factors include:
- A family history of thyroid disease
- A history or previous diagnosis of an autoimmune disease
- History of neck irradiation
- Previous thyroid surgery
- Lithium or amiodarone medication usage
- Iodine excess or deficiency in the diet
- Certain genetic disorders
How Is Thyroid Disease Diagnosed?
The first steps towards diagnosing thyroid disease are a careful history and physical exam. Looking at the hair and skin, evaluating the heart rate and rhythm, looking for trends in weight gain or loss, and evaluating the shape and size of the thyroid gland can all provide clues about how well the thyroid gland is functioning.
Blood tests are used to measure hormone levels and to assess thyroid function.
Thyroid-Stimulating Hormone (TSH)
TSH levels are typically ordered to screen for thyroid function. When the thyroid gland is not functioning properly, changes in TSH levels may precede changes in T4 and T3. Except in very rare cases when the problem is with the pituitary gland or the hypothalamus rather than the thyroid gland, a normal TSH level rules out thyroid disease due to increased or decreased thyroid hormone production.
T4 can circulate in the bloodstream, either free or bound to protein. Total T4 is a measurement of bound and free T4. Free T4 is the unbound portion of T4 that can enter cells and exert an effect.
- A high TSH and a low free T4 level indicate primary hypothyroidism caused by thyroid gland disease. The pituitary gland is prodding the thyroid gland to produce more thyroid hormone by increasing TSH levels, but the thyroid gland is not responding.
- A low TSH and a low T4 level indicate primary hypothyroidism caused by a pituitary gland problem. T4 levels are low. The pituitary gland should react by increasing TSH levels, but it does not. The lack of response indicates that the pituitary gland is malfunctioning.
- Primary hyperthyroidism is indicated by a low TSH and a high free T4. Because the free T4 level is high, the pituitary gland reduces TSH production appropriately.
Most T3 is created by removing an iodine molecule from T4. In a small subset of people with hyperthyroidism, only T3 is elevated.
Subclinical Thyroid Disease
The prevalence of mild or subclinical thyroid disease increases with age and affects 7% to 10% of women over the age of 60. Subclinical disease is defined as an abnormal TSH level with normal T4, free T4, T3, and free T3 levels. TSH levels are elevated in subclinical hypothyroidism, but T3 and T4 levels are normal. Subclinical hyperthyroidism is defined by a low TSH level with normal T3 and T4 levels.
|Summary of Lab Findings||TSH||Free T4||Free T3|
|No disease (euthyroid)||Normal||Normal||Normal|
|Hyperthyroidism before symptoms develop or early pregnancy||Low||Normal||Normal|
|Hypothyroidism before symptoms develop||High||Normal||Normal|
Thyroid Antibody Tests
A healthy immune system fights foreign invaders such as bacteria and viruses. Sometimes immune cells have difficulty distinguishing between cells that belong to the body and foreign invaders. In many people with thyroid disease, white blood cells called lymphocytes attack the thyroid gland by producing antibodies against thyroid proteins. Two common thyroid antibodies are thyroid peroxidase antibody and thyroglobulin antibody. These antibodies can be measured to help diagnose autoimmune causes of thyroid disease. Hashimoto’s thyroiditis is an example of autoimmune hypothyroidism. Antibodies can also bind to and stimulate the TSH receptor, resulting in excessive TSH production and hyperthyroidism. Graves’ disease is an example of autoimmune hyperthyroidism.
Radioactive Iodine Uptake
A radioactive iodine test is a test of thyroid activity. It measures the amount of radioactive iodine drawn from the blood into the thyroid gland. Measuring the amount of radioactive iodine used by the thyroid gland is a good indicator of its overall function.
- Too much radioactive iodine uptake can indicate hypothyroidism
- Too little radioactive iodine uptake can indicate hyperthyroidism
- Too much radioactive iodine uptake in a specific part of the thyroid gland can indicate a thyroid nodule
How Is Thyroid Disease Treated?
Treatment for thyroid disease will depend on whether the thyroid produces too much or too little thyroid hormone.
Thyroid hormone can be replaced by taking synthetic thyroid hormone (levothyroxine) daily. The dosage is carefully titrated to replace thyroid hormone without giving too much. Thyroid hormone is given for life because whatever causes the thyroid gland to decrease thyroid hormone production is generally permanent. Thyroid function is monitored regularly to see how well thyroid hormone replacement mimics the function of natural T4 hormone.
There are several treatment options for hyperthyroidism. Factors such as age, the severity of hyperthyroidism, and the presence of other medical conditions are used to determine the best treatment option.
Antithyroid medications block the thyroid gland’s ability to produce thyroid hormone. Antithyroid medications are well known for their potential to cause side effects and allergic reactions.
The thyroid gland quickly absorbs radioactive iodine from the bloodstream. Once it enters the thyroid gland, it destroys the thyroid cells that take it up. As a result, the thyroid shrinks in size and decreases its production of thyroid hormone. In the U.S., over 70% of adults who develop hyperthyroidism are treated with radioactive iodine.
Hyperthyroidism can be treated by removing most or all of the thyroid gland. However, the surgery can be risky if hyperthyroidism is not controlled first. After the thyroid is removed, thyroid hormone replacement will be needed. Thyroid disease is common, and the prevalence rises with age. Knowing the symptoms of thyroid disease can lead to earlier diagnosis and treatment. Most thyroid conditions are permanent and necessitate the use of lifelong thyroid replacement. It is important to take thyroid medication daily as directed to decrease the risk of symptoms. However, taking too much thyroid hormone can also cause symptoms and affect the heart and bone.