Thyroid gland: functions, disorders, signs, and treatment

Reviewed by Caitlin Goodwin DNP, CNM, RN

The thyroid gland is a small gland located in front of the trachea (windpipe) at the front of the neck. It is narrower in the middle, with two wider lobes extending around the sides of the throat, giving it a butterfly-like shape. The thyroid gland creates and releases hormones that are vital for the body’s cells to function properly.

Thyroid disorders are common and occur more frequently in females. However, thyroid disorders can affect anyone, including men, teenagers, children, and babies. According to Cleveland Clinic, about 20 million people in the United States have some type of thyroid condition.

Functions of the thyroid gland

The thyroid gland makes two hormones that are secreted into the blood: thyroxine and triiodothyronine. Thyroxine contains four iodine atoms and is generally called T4. Triiodothyronine contains three iodine atoms and is called T3.

T4 is converted into T3 in the body. T3 is the more biologically active hormone and affects the activity of cells and tissues throughout the body.

The thyroid plays an important role in regulating metabolism. Metabolism is the process that transforms food into energy. This energy is used throughout the body to keep body systems functioning efficiently.

Both thyroid hormones, T3 and T4, increase the basal metabolic rate. This has the following effects:

• Stored energy is broken down more quickly, increasing the body’s metabolism
• The brain and nervous system develop and mature in children
• Growth and development are supported in children
• Body temperature increases
• Heart rate and cardiac activity increase
• The nervous system becomes more active, which can affect concentration and reflexes

Disorders

The thyroid is responsible for producing hormones that play a vital role throughout the body. If the thyroid produces too little or too much hormone, it can lead to a thyroid disorder. Common thyroid disorders include hypothyroidism, hyperthyroidism, thyroiditis, Hashimoto’s thyroiditis, Graves’ disease, and goiter.

Hypothyroidism

In hypothyroidism, the thyroid gland does not produce enough thyroid hormone. Sometimes surgery to remove part or all of the thyroid gland, radiation treatment, autoimmune disease, certain medications, or thyroid inflammation can cause hypothyroidism. In the United States, nearly 5 out of 100 people ages 12 years and older have hypothyroidism.

Symptoms of hypothyroidism can include:

• Weakness
• Fatigue
• Slow heartbeat (bradycardia)
• Dry skin
• Memory problems
• Depression
• Weight gain
• Increased sensitivity to cold
• Constipation

Severe untreated hypothyroidism may rarely lead to myxedema coma, a life-threatening condition.

Conditions that can lead to hypothyroidism include:

Thyroiditis

Thyroiditis is inflammation or swelling of the thyroid gland. It can reduce the amount of hormone produced by the thyroid.

Hashimoto’s thyroiditis

Hashimoto’s thyroiditis is the most common cause of hypothyroidism in the United States. It can occur at any age, but it is more common in females. This disorder occurs when the immune system mistakenly attacks and damages the thyroid gland, reducing its ability to produce hormones.

Symptoms of Hashimoto’s thyroiditis can include:

• Mild weight gain
• Fatigue
• Depression
• Constipation
• Thinning hair
• Dry skin
• Pale or puffy face
• Increased sensitivity to cold
• Enlarged thyroid gland (goiter)

Postpartum thyroiditis

This condition affects some people within the first year after giving birth. It is usually temporary, although some people may later develop permanent hypothyroidism.

Iodine deficiency

Iodine is necessary for the thyroid to produce hormones. Severe iodine deficiency is a major cause of hypothyroidism in some parts of the world. However, iodine deficiency is uncommon in the United States because iodine is added to many foods and table salt.

Congenital hypothyroidism

In some newborns, the thyroid gland does not develop properly or does not function normally at birth. Without treatment, congenital hypothyroidism can lead to developmental and growth problems. Newborn screening tests are routinely performed after birth to detect this condition early.

Hyperthyroidism

In hyperthyroidism, the thyroid gland is overactive and produces too much thyroid hormone. About 1 out of 100 Americans ages 12 and older have hyperthyroidism. It is more common in women.

Excess thyroid hormone can cause:

• Weight loss
• Muscle weakness
• Thin skin
• Restlessness
• Nervousness
• Rapid or irregular heartbeat
• Irritability
• Increased sweating
• Shaking or tremors
• Anxiety
• Trouble sleeping
• Brittle hair and nails
• Bulging eyes (commonly associated with Graves’ disease)

Conditions that can lead to hyperthyroidism include:

Graves’ disease

Graves’ disease is an autoimmune disorder in which the immune system mistakenly attacks the thyroid gland, causing it to produce excessive amounts of thyroid hormone.

This disorder can occur at any age but is more common in females between the ages of 20 and 30. Risk factors may include family history, smoking, stress, and pregnancy.

Symptoms can include:

• Fatigue
• Hand tremors
• Anxiety
• Irritability
• Excessive sweating
• Rapid or irregular heartbeat
• Difficulty sleeping

Subacute thyroiditis

Subacute thyroiditis is an inflammatory thyroid condition that may cause neck pain and temporary changes in thyroid hormone levels. In some cases, the thyroid releases stored hormones into the bloodstream, which can temporarily cause hyperthyroidism before thyroid levels return to normal.

Excessive iodine

Excessive iodine intake may trigger hyperthyroidism in some individuals, especially those with underlying thyroid disease. High iodine levels may occur from certain medications, such as amiodarone, contrast dyes used in imaging studies, supplements, or excessive intake of iodine-containing products.

Goiter

A goiter is a non-cancerous enlargement of the thyroid gland. Although iodine deficiency is a major cause of goiter worldwide, goiters can also result from autoimmune thyroid diseases such as Hashimoto’s thyroiditis and Graves’ disease, thyroid nodules, thyroid inflammation, pregnancy, or other thyroid conditions.

A goiter can affect people of any age. It is more common in females and in adults over the age of forty.

Small goiters may not cause symptoms. However, larger goiters can cause:

• Coughing or wheezing
• Hoarseness
• Swelling or tightness in the neck
• Difficulty breathing
• Difficulty swallowing

Treatment

Treatment depends on the type and severity of the thyroid disorder.

Hypothyroidism is commonly treated with thyroid hormone replacement medication, such as levothyroxine.

Hyperthyroidism may be treated with medications that reduce thyroid hormone production, radioactive iodine therapy, or surgery to remove part or all of the thyroid gland.

Goiters and thyroid nodules may only require monitoring, but some cases require medication, radioactive iodine treatment, or surgery depending on the cause, size, and symptoms.

People who have had their thyroid removed usually need lifelong thyroid hormone replacement therapy.

Prevention

Hypothyroidism and hyperthyroidism usually cannot be completely prevented. In developing countries, hypothyroidism is often caused by iodine deficiency. However, iodine deficiency is uncommon in the United States because iodine is added to table salt and many foods.

Hyperthyroidism is commonly caused by Graves’ disease, an autoimmune disorder that cannot usually be prevented. Taking more thyroid hormone medication than prescribed may also lead to hyperthyroidism.

Although thyroid disease cannot always be prevented, early diagnosis, regular medical follow-up, and proper treatment can help reduce complications and improve quality of life.

Works cited

• Thyroid disease, 2024. Cleveland Clinic. my.clevelandclinic.org/health/diseases/8541-thyroid-disease
• Hypothyroidism (underactive thyroid), 2021. NIDDK. niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism
• Hyperthyroidism (overactive thyroid), 2021. NIDDK. niddk.nih.gov/health-information/endocrine-diseases/hyperthyroidism
• Hashimoto’s disease, 2021. NIDDK. niddk.nih.gov/health-information/endocrine-diseases/hashimotos-disease
• In brief: how does the thyroid gland work?, 2024. NCBI Bookshelf/InformedHealth.org. ncbi.nlm.nih.gov/books/NBK279388