Thyroid disorders affect millions of people worldwide, causing a wide range of symptoms that can significantly impact daily life. From unexplained fatigue to sudden weight changes, these conditions occur when the small butterfly-shaped gland in your neck produces either too much or too little hormone.

Epidemiology

Thyroid disease is remarkably common in the United States and around the world. Approximately 20 million Americans currently live with some form of thyroid condition, making it one of the most widespread endocrine disorders^[1]. The numbers reveal an important pattern: thyroid problems affect far more women than men throughout their lives.

The statistics show that one in eight women will develop thyroid problems during their lifetime, while men face significantly lower rates^[7]. More specifically, the annual incidence of hypothyroidism (underactive thyroid) in women reaches 4.1 to 4.98 per 1,000 people, compared to only 0.6 to 0.88 per 1,000 men. For hyperthyroidism (overactive thyroid), women experience rates of 0.77 to 0.8 per 1,000 annually, while men see rates of just 0.14 per 1,000^[1].

Age plays a crucial role in thyroid disease development. The likelihood of developing thyroid problems increases as people grow older, with those over 60 years facing higher risks^[8]. Among older adults, hypothyroidism becomes particularly common, affecting up to 15 percent of adults aged 70 and older^[8]. Nursing home residents show even higher rates, with up to 25 percent experiencing hypothyroidism.

Certain populations face elevated risk. Nearly five percent of the general population has an underactive thyroid, while overactive thyroid affects slightly more than one percent^[3]. Babies can also be affected: about 1 in every 2,000 to 4,000 newborns are born with congenital hypothyroidism, a condition where the thyroid is missing or underactive from birth^[1].

Causes

Thyroid disease develops when something interferes with the thyroid gland’s ability to produce the right amount of hormones. The causes vary depending on whether the thyroid becomes underactive or overactive, and understanding these differences helps explain why treatment approaches differ.

The most common cause of hypothyroidism in developed countries is Hashimoto’s disease, a lifelong autoimmune condition where the immune system mistakenly attacks the thyroid gland^[1]. In this condition, the body’s defense system treats thyroid tissue as foreign, gradually damaging the gland until it cannot produce enough hormone. This autoimmune process often develops slowly over time, which explains why many people don’t notice symptoms immediately.

Iodine plays a critical role in thyroid hormone production. The thyroid gland needs this mineral to manufacture thyroid hormone, so when people don’t get enough iodine through their diet, hypothyroidism can develop^[1]. This remains the most common cause of hypothyroidism in countries where iodized salt isn’t widely available. However, in regions with sufficient dietary iodine, this cause is rare. Interestingly, too much iodine can also cause problems, leading to excessive thyroid hormone production in some cases^[1].

Medical treatments frequently trigger thyroid dysfunction. Surgical removal of part or all of the thyroid gland naturally reduces or eliminates hormone production. Radiation treatment to the neck or thyroid area can damage thyroid cells, preventing them from working properly. Certain medications also interfere with thyroid function, including amiodarone (a heart medication), immune checkpoint inhibitors, lithium, and interferon-alfa^[1][13].

For hyperthyroidism, Graves’ disease stands as the most frequent culprit. This chronic autoimmune condition causes the thyroid to produce too much hormone and accounts for about 70 percent of all hyperthyroidism cases^[1][6]. In Graves’ disease, the immune system creates antibodies that stimulate the thyroid, essentially tricking it into overproducing hormones.

Thyroid nodules, which are abnormal lumps or growths on the thyroid gland, can also cause hormone imbalances. When these nodules become hyperfunctioning, they produce thyroid hormone independently of the body’s normal control systems, leading to excess hormone levels^[1].

Thyroiditis, or inflammation of the thyroid gland, creates a unique pattern. It typically causes temporary hyperthyroidism first as the inflamed gland leaks stored hormones into the bloodstream. This is often followed by temporary or permanent hypothyroidism as the gland becomes depleted or damaged^[1].

Pregnancy-related thyroid problems affect an estimated 5 percent of birthing parents within the year after delivery. This condition, called postpartum thyroiditis, usually follows a pattern of hyperthyroidism first, then hypothyroidism, and is often temporary^[1].

Risk Factors

Certain characteristics and circumstances increase the likelihood of developing thyroid disease. Understanding these risk factors helps identify people who may benefit from closer monitoring or earlier testing when symptoms appear.

Gender represents the single most significant risk factor. Women face dramatically higher rates of thyroid disorders throughout their lives compared to men. This gender difference appears across all types of thyroid disease, though researchers haven’t fully explained why women are more susceptible^[7].

Age increases vulnerability to thyroid problems. People older than 60 years have substantially higher rates of thyroid dysfunction, particularly hypothyroidism^[5][16]. As the body ages, the thyroid gland may function less efficiently, and older adults also have greater exposure to other risk factors over their lifetime.

Family history matters considerably. Having relatives with thyroid disease raises your own risk, as genetic factors appear to play a role in thyroid disorders^[16]. The connection is particularly strong with autoimmune thyroid conditions like Hashimoto’s disease and Graves’ disease.

Previous thyroid problems predict future issues. Anyone who has had thyroid trouble before, such as a goiter (enlarged thyroid), faces increased risk of developing additional thyroid conditions. Similarly, people who have had surgery or radiation treatment for a thyroid problem are more likely to experience thyroid dysfunction later^[16].

Pregnancy and recent childbirth create a window of vulnerability. Women who are currently pregnant or who delivered a baby within the past six months have elevated risk of developing thyroid problems^[16]. The hormonal changes and immune system shifts associated with pregnancy can trigger thyroid dysfunction in susceptible individuals.

Certain medical conditions cluster with thyroid disease. People with other autoimmune disorders, including type 1 diabetes, rheumatoid arthritis, lupus, or Sjogren’s syndrome, have higher thyroid disease rates^[16]. This connection reflects the underlying immune system dysfunction that drives multiple autoimmune conditions.

Some genetic disorders carry thyroid risks. Turner syndrome, a genetic condition affecting females, increases the likelihood of thyroid problems. Pernicious anemia, where the body cannot produce enough healthy red blood cells due to vitamin B12 deficiency, also raises thyroid disease risk^[16].

Radiation exposure to the neck, chest, or thyroid area—whether from medical treatments or environmental sources—can damage thyroid tissue and lead to dysfunction later in life^[16]. Even radiation treatment received years earlier can eventually affect thyroid function.

Symptoms

Thyroid disease produces a wide range of symptoms that depend on whether the gland is producing too much or too little hormone. Unfortunately, these symptoms often develop slowly and can easily be mistaken for other health problems or simply attributed to aging or stress, which delays diagnosis for many people^[1].

When the thyroid produces too little hormone, the body’s processes slow down. People with hypothyroidism commonly experience overwhelming tiredness or fatigue that doesn’t improve with rest. They may gain weight despite not eating more than usual, and find themselves feeling cold even when others are comfortable^[5]. The skin becomes dry and rough, and hair may become thin, coarse, or fall out more than normal.

Mental and emotional changes accompany physical symptoms in hypothyroidism. Many people struggle with poor concentration, difficulty thinking clearly, or problems with memory^[1]. Depression and low mood are common, sometimes severe enough that people initially seek help for mental health concerns rather than recognizing a thyroid problem.

The voice may become hoarse or croaky without an obvious cause like a cold^[5]. Constipation develops as the digestive system slows down. Muscles feel weak, achy, tender, or stiff. The heart rate may slow, and women often experience heavier than usual or irregular menstrual periods. Some people develop fertility problems^[5].

In contrast, hyperthyroidism speeds up the body’s processes, creating an entirely different symptom pattern. Weight loss occurs despite normal or increased eating. The heart may race or beat irregularly, which some people find frightening. Excessive sweating develops, and people become intolerant to heat^[3].

Emotional symptoms of hyperthyroidism include restlessness, agitation, anxiety, and nervousness. Hands develop a fine tremor that makes detailed tasks difficult^[3]. Sleep becomes disturbed, and people may experience frequent bowel movements or diarrhea. Women may notice irregular menstrual flow. The skin becomes thin, and hair may thin as well.

A visible swelling in the neck, called a goiter, can develop with either hypothyroidism or hyperthyroidism. This enlarged thyroid may be noticeable when looking in a mirror or wearing certain clothing. In some cases, a large goiter causes difficulty breathing or swallowing^[5].

Some people with hyperthyroidism, particularly those with Graves’ disease, develop eye problems. The eyes may look enlarged or bulging, feel gritty or sore, or become sensitive to light. This condition, called thyroid eye disease, can be uncomfortable and distressing^[9].

Older adults with hyperthyroidism sometimes present differently. They may experience irregular heart rhythms, heart failure, or mental confusion. Without treatment, severe hyperthyroidism can lead to a “thyroid storm,” a critical situation involving high blood pressure, heart failure, and fever that requires urgent medical attention^[3].

Prevention

Unlike some diseases, most thyroid disorders cannot be prevented through specific lifestyle changes or interventions. The conditions that cause thyroid disease—particularly autoimmune disorders like Hashimoto’s disease and Graves’ disease—develop due to complex interactions between genetic factors and environmental influences that are not fully understood or controllable^[7].

However, maintaining overall health can help reduce some risk factors and may lessen the impact of thyroid disorders when they do occur. Managing stress represents one area where individuals have some control. Illness, pregnancy, and chronic stress can all impact thyroid function, so developing effective stress management strategies may help support thyroid health^[7]. This might include regular exercise, maintaining healthy relationships, and finding personalized approaches to reducing stress in daily life.

Exercise benefits thyroid health in multiple ways. Regular physical activity helps regulate metabolism, supports hormone balance, and reduces inflammation throughout the body^[17]. The activity doesn’t need to be intense to be helpful—a balanced routine including cardiovascular exercise, strength training, and flexibility work supports overall thyroid function.

Adequate sleep plays a crucial role. Getting seven to nine hours of quality sleep each night supports hormone production and helps regulate metabolism^[17]. Sleep disturbances often emerge as early signs of thyroid dysfunction, so prioritizing consistent, sufficient sleep supports thyroid health.

For people living in areas with insufficient dietary iodine, ensuring adequate iodine intake is important. The thyroid requires iodine to manufacture thyroid hormones, so consuming iodine-rich foods like seaweed, fish, dairy products, and iodized salt supports proper thyroid function^[17]. However, in countries like the United States and United Kingdom where iodine is widely available in the food supply, deficiency is rare and supplementation beyond dietary sources is generally unnecessary.

In fact, excessive iodine can cause problems. People should avoid products like kelp and sea moss supplements that contain very high amounts of iodine, as these can interfere with thyroid function and wellbeing^[18]. Unless someone comes from an area with known iodine insufficiency, iodine supplements are not recommended and may actually worsen thyroid problems.

Limiting exposure to environmental toxins may help protect thyroid function. Pollutants, certain chemicals, and heavy metals can interfere with how the thyroid works^[17]. Using natural cleaning products when possible, filtering drinking water, and being mindful of environmental pollutants reduces this exposure.

A balanced diet rich in nutrients supports thyroid health, though no specific foods or dietary supplements can treat or prevent thyroid disorders. Eating a variety of fresh, whole foods—including fruits, vegetables, lean proteins, and whole grains—while avoiding highly processed foods provides the nutrients the thyroid needs to function properly^[18].

Regular health checkups allow for early detection of thyroid problems. While population-wide screening for thyroid disease in asymptomatic adults has uncertain benefits^[13], people with risk factors or symptoms should discuss testing with their healthcare provider. Earlier diagnosis enables earlier treatment, which can prevent complications and reduce the impact of thyroid disease on quality of life.

Pathophysiology

The thyroid gland sits at the base of the neck, shaped like a small butterfly with two lobes connected by a bridge of tissue called the isthmus^[9]. Despite its modest size—each lobe is roughly the size of half a plum—this gland wields enormous influence over bodily functions through the hormones it produces and releases into the bloodstream.

The thyroid manufactures two main hormones: thyroxine (T4) and triiodothyronine (T3). T4 contains four atoms of iodine, while T3 contains three. The thyroid secretes mostly T4, which then travels throughout the body. In cells and tissues, T4 gets converted into T3, which is the biologically active form that actually influences how cells work^[9].

These thyroid hormones control the speed of metabolism—the process by which the body converts food into energy. Every cell in the body needs thyroid hormone to function properly. The hormones affect nearly every organ system, regulating breathing, heart rate, body weight, digestion, body temperature, muscle strength, menstrual cycles, cholesterol levels, and even mood and mental processes^[2][9].

Think of thyroid hormones as setting the pace for all the body’s cells and organs. When hormone levels are correct, everything runs smoothly. But when production becomes imbalanced, either too high or too low, the effects ripple throughout the entire body.

The thyroid doesn’t work independently. A sophisticated control system regulates hormone production. The hypothalamus in the brain monitors thyroid hormone levels in the blood. When levels drop too low, the hypothalamus signals the pituitary gland, which sits at the base of the brain. The pituitary then releases thyroid-stimulating hormone (TSH) into the bloodstream^[3].

TSH travels to the thyroid and stimulates it to produce more thyroid hormones. Conversely, when thyroid hormone levels rise too high, the pituitary releases less TSH, signaling the thyroid to slow production. This feedback loop normally maintains thyroid hormones within a narrow, healthy range^[7].

In hypothyroidism, the thyroid cannot produce adequate amounts of hormone despite receiving normal or even increased TSH signals. Without enough thyroid hormone, the metabolic rate slows. Heart rate decreases, sometimes causing bradycardia (abnormally slow heartbeat). The digestive system becomes sluggish, leading to constipation. Body temperature regulation falters, making people feel cold. The brain functions less efficiently, causing problems with memory and concentration. Metabolism of fats changes, often leading to elevated cholesterol levels^[5].

In hyperthyroidism, the thyroid produces excessive amounts of hormone, either because it receives abnormal stimulation (as in Graves’ disease) or because parts of the gland function independently of normal controls (as with toxic nodules). The metabolic rate accelerates. The heart beats faster and may develop irregular rhythms. The digestive system speeds up, causing frequent bowel movements. Body temperature regulation shifts, producing heat intolerance and excessive sweating. The increased metabolic rate burns through energy stores, causing weight loss despite adequate food intake^[3].

In autoimmune thyroid diseases like Hashimoto’s and Graves’ disease, the immune system produces antibodies that target the thyroid. In Hashimoto’s disease, these antibodies attack and gradually destroy thyroid tissue, reducing the gland’s ability to produce hormone. In Graves’ disease, antibodies mimic TSH, continuously stimulating the thyroid to produce excessive hormone regardless of the body’s actual needs^[1].

Thyroiditis causes inflammation that damages thyroid cells. Initially, this damage causes the gland to leak stored hormone into the bloodstream, temporarily raising hormone levels and causing hyperthyroid symptoms. Once the stored hormone is depleted, the damaged gland cannot produce enough new hormone, leading to hypothyroidism^[1].

When thyroid hormone levels remain abnormal for extended periods, more serious complications can develop. Chronic hypothyroidism can contribute to heart problems, including heart failure, because the heart needs adequate thyroid hormone to pump efficiently. It can also cause myxedema, a condition where substances accumulate in the skin and other tissues, causing swelling, particularly in the face. In extreme cases, severe untreated hypothyroidism leads to myxedema coma, where body functions slow to life-threatening levels^[5][16].

Untreated hyperthyroidism can lead to heart problems including arrhythmias (irregular heart rhythms) and heart failure. The constant metabolic acceleration puts strain on the cardiovascular system. It can also cause loss of bone density, increasing fracture risk. In thyroid storm, metabolic processes accelerate dangerously, causing fever, severe heart problems, and altered mental state^[3].