The thyroid is a small, butterfly-shaped gland at the front of the neck, but it has a surprisingly large influence on health.
It makes hormones that help control how quickly the body uses energy and also affects heart rate, body temperature, digestion and many other functions.
When the thyroid produces too little or too much hormone, many parts of the body can be affected. Two of the most common problems are hypothyroidism, when the thyroid is underactive, and hyperthyroidism, when it is overactive.
An underactive thyroid slows many body processes. People may feel unusually tired, gain weight, become sensitive to cold, develop dry skin or experience problems with concentration and mood.
An overactive thyroid can produce almost the opposite pattern. It may cause weight loss, a racing or irregular heartbeat, sweating, shaking, anxiety and difficulty sleeping.
Autoimmune disease is one of the major causes of thyroid disorders. This happens when the immune system, which normally attacks viruses and other threats, mistakenly targets the body’s own tissues.
Hashimoto’s thyroiditis is a common example. The immune system gradually attacks the thyroid, which can damage the gland and reduce its ability to make hormones. It is a major cause of hypothyroidism.
Graves’ disease works differently. In this condition, abnormal immune activity stimulates the thyroid to make too much hormone, leading to hyperthyroidism. Some people with Graves’ disease can also develop eye problems.
Scientists do not know exactly why these autoimmune conditions begin. Research suggests that inherited genes and outside influences both contribute, which helps explain why thyroid disease sometimes runs in families without affecting every family member.
Iodine is another important part of thyroid health because the gland needs it to make thyroid hormones. Too little iodine can cause thyroid problems, but very high iodine intake can also disturb thyroid function in some people.
Many countries add iodine to salt or other foods to prevent deficiency. Because iodine needs vary and excess amounts can sometimes be harmful, people should be cautious about taking high-dose iodine supplements unless a healthcare professional recommends them.
Radiation can also damage thyroid tissue. People who have received radiation treatment around the head or neck, particularly at younger ages, may have a higher risk of developing thyroid problems later.
Smoking has also been linked with thyroid disease, particularly Graves’ disease and its eye complications. Tobacco smoke contains substances that can affect the thyroid and immune system in several ways.
Women develop thyroid disorders much more often than men. The reasons are not completely understood, but differences in immune function and hormonal changes are thought to contribute. Pregnancy and the period after childbirth can also trigger temporary or lasting thyroid problems in some women.
Certain medicines can interfere with thyroid function as well. Lithium, used to treat some mental health conditions, is one example. Other medicines can increase or decrease thyroid hormone activity, which is why doctors sometimes monitor thyroid blood tests during treatment.
Inflammation of the thyroid can also occur after some infections. In these cases, stored thyroid hormone may leak into the bloodstream at first, sometimes causing a temporary overactive phase before thyroid function returns to normal or becomes underactive.
Stress is sometimes blamed for thyroid disease, but the relationship is complicated. Stress affects many body systems, yet it should not be assumed to be the main cause of a thyroid disorder without medical testing.
Doctors usually diagnose thyroid problems using symptoms, a physical examination and blood tests that measure thyroid-related hormones. Treatment depends on the cause and whether the gland is producing too little or too much hormone.
Hypothyroidism is commonly treated with a replacement thyroid hormone taken regularly. Hyperthyroidism may be treated with medicines, radioactive iodine or surgery, depending on the person’s condition and the cause.
Research on thyroid disease is published across major endocrinology and medical journals, and organizations such as the American Thyroid Association continue to update clinical guidance as evidence develops.
Although thyroid disorders can cause symptoms throughout the body, most can be managed effectively once they are correctly diagnosed.
Anyone with ongoing symptoms that could suggest a thyroid problem should discuss them with a healthcare professional rather than relying on symptoms alone. A simple blood test can often provide important clues and help doctors choose the right treatment.
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