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Hypothyroidism is when the thyroid gland does not produce enough thyroid hormones to meet the needs of the body. The thyroid is underactive.

The opposite is hyperthyroidism, where the thyroid produces too much thyroid hormone. However, the link between hyperthyroidism and hypothyroidism is complex, and one can lead to the other, in certain circumstances.

Thyroid hormones regulate metabolism, or the way the body uses energy. If thyroxine levels are low, many of the body's functions slow down.

About 4.6 percent of the population aged 12 years and above in the United States has hypothyroidism.

The thyroid gland is found in the front of the neck below the larynx, or voice box, and has two lobes, one on each side of the windpipe.

It is an endocrine gland, made up of special cells that make hormones. Hormones are chemical messengers that relay information to the organs and tissues of the body, controlling processes such as metabolism, growth, and mood.

The production of thyroid hormones is regulated by thyroid-stimulating hormone (TSH), which is made by the pituitary gland.

This, in turn, is regulated by the hypothalamus, a region of the brain. TSH ensures that enough thyroid hormones are made to meet the needs of the body.

Fast facts on hypothyroidism

Here are some key points about hypothyroidism. More detail and supporting information is in the main article.

  • The thyroid gland produces two thyroid hormones, TS3 and TS4.
  • These hormones regulate the body's metabolism.
  • The most common cause of hypothyroidism in the U.S. is Hashimoto's disease.
  • Symptoms of hypothyroidism include fatigue, cold intolerance, and joint and muscle pain.

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Hypothyroidism refers to the underproduction of hormones in the thyroid gland. It has a wide range of symptoms.

Thyroid hormones affect multiple organ systems, so the symptoms of hypothyroidism are wide-ranging and diverse.

The thyroid creates two thyroid hormones, triiodothyronine (T3) and thyroxine (T4). These regulate metabolism, and they also affect the following functions:

  • brain development
  • breathing
  • heart and nervous system functions
  • body temperature
  • muscle strength
  • skin dryness
  • menstrual cycles
  • weight
  • cholesterol levels

Symptoms of hypothyroidism commonly include, but are not limited to:

  • fatigue
  • weight gain
  • cold intolerance
  • slowed heart rate, movements, and speech
  • joint and muscle pain, cramps, and weakness
  • constipation
  • dry skin
  • thin, brittle hair or fingernails
  • decreased sweating
  • pins and needles
  • heavy periods, or menorrhagia
  • weakness
  • high cholesterol
  • puffy face, feet, and hands
  • insomnia
  • balance and co-ordination issues
  • loss of libido
  • recurrent urinary and respiratory tract infections
  • anemia
  • depression

If left untreated, the following symptoms can manifest:

  • hoarseness
  • puffiness in the face
  • thinned or missing eyebrows
  • slow heart rate
  • hearing loss

If it develops in children or teenagers, the signs and symptoms are generally the same as adults.

However, they may also experience:

  • poor growth
  • delayed development of teeth
  • poor mental development
  • delayed puberty

Hypothyroidism develops slowly. Symptoms may go unnoticed for a long time, and they may be vague and general.

Symptoms vary a great deal between individuals, and they are shared by other conditions. The only way to obtain a concrete diagnosis is through a blood test.

Treatment for hypothyroidism focuses on supplementing the thyroid hormone. At present, doctors cannot cure hypothyroidism but they can help people to control it in most cases.

Synthetic thyroxine

To replenish levels, doctors usually prescribe synthetic thyroxine, a medication that is identical to the T4 hormone. Doctors may recommend taking this in the morning before eating each day.

Dosage is determined by the patient's history, symptoms, and current TSH level. Doctors will regularly monitor the patient's blood to determine if the dosage of synthetic T4 needs to be adjusted.

Regular monitoring will be required, but the frequency of blood tests will likely decrease over time.

Iodine and nutrition

Iodine is an essential mineral for thyroid function. Iodine deficiency is one of the most common causes of goiter development, or abnormal enlargement of the thyroid gland.

Maintaining adequate iodine intake is important for most people, but those with autoimmune thyroid disease can be particularly sensitive to the effects of iodine, meaning that it can trigger or worsen hypothyroidism.

They should inform their doctor if they are sensitive to the effects of iodine.

People with hypothyroidism should discuss any major dietary changes with their doctor, especially when starting a high fiber diet, or eating lots of soy or cruciferous vegetables.

Diet can affect the way in which the body absorbs thyroid medication.

During pregnancy, iodine requirements increase. Using iodized salt in the diet and taking prenatal vitamins can maintain the required levels of iodine.

Iodine supplements are available for purchase online.

Hypothyroidism can normally be managed appropriately by following the advice of a qualified healthcare practitioner. With appropriate treatment, thyroid hormone levels should return to normal.

In most cases, medications for hypothyroidism will need to be taken for the rest of the patient's life.

Prevention

There is no way to prevent hypothyroidism, but people who may have a higher risk of thyroid problems, for example, women during pregnancy, should check with their doctor about the need for additional iodine.

Screening is not recommended for those who do not have symptoms, unless they have the following risk factors:

  • a history of autoimmune disease
  • previous radiation treatment to the head or neck
  • a goiter
  • family history of thyroid problems
  • use of medications known to affect thyroid function

These people can be tested for early signs of the condition. If tests are positive, they can take measures to prevent the disease from progressing.

There is no evidence that a particular diet will prevent hypothyroidism, and there is no way to prevent hypothyroidism unless you live in a region with low iodine levels in the diet, for example, some parts of Southeast Asia and Africa.

No specific diet is recommended for hypothyroidism, but individuals should follow a varied, well-balanced diet that is not high in fat or sodium.

In addition, those with autoimmune Hashimoto's may benefit from following a gluten-free diet. Research suggests a link between celiac disease and autoimmune thyroid disease, and both have inflammatory components. Avoiding gluten may help in nonceliac autoimmune diseases, but it is important to speak to a doctor first before cutting out foods that contain gluten.

Other foods and nutrients may be hazardous, especially if consumed in large quantities.

These include:

  • soya, as it can affect thyroxine absorption
  • iodine, found in kelp and other seaweeds, and in supplements, including some multivitamins
  • iron supplements, as they can affect thyroxine absorption
  • cruciferous vegetables, such as cauliflower, kale, and cabbage may contribute to a goiter, but only in very large amounts

Consuming additional iodine can interfere with the balance involved in treatment. If hyperthyroidism develops, iodine can be hazardous.

Any changes to diet or supplementation should be discussed with a doctor.

Hypothyroidism can occur if the thyroid gland fails to work properly, or if the thyroid gland is not stimulated properly by the hypothalamus or pituitary gland.

Hashimoto's disease

The most common cause of hypothyroidism in the U.S. is Hashimoto's disease, also known as chronic lymphocytic thyroiditis or autoimmune thyroiditis.

Hashimoto's disease is an autoimmune disease, a disorder in which the immune system attacks the body's own cells and organs.

The condition causes the immune system to attack the thyroid gland, leading to inflammation and interfering with its ability to produce thyroid hormones.

Thyroiditis

Thyroiditis is an inflammation of the thyroid gland. It causes thyroid hormones to leak into the blood, raising their overall levels and leading to hyperthyroidism. After 1 to 2 months, this may develop into hypothyroidism.

Thyroiditis can be caused by viral or bacterial infection, an autoimmune condition or following pregnancy.

Congenital hypothyroidism

In cases of congenital hypothyroidism, the thyroid gland does not function properly from birth.

This can lead to physical and mental growth problems, but early treatment can prevent these complications. Most newborns in the U.S. are screened for hypothyroidism.

Thyroid surgery and treatment as causes of hypothyroidism

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Hypothyroidism can occur after part of the thyroid is removed during surgery.

Thyroid treatment and surgery can lead to hypothyroidism.

Several conditions such as hyperthyroidism, goiters, thyroid nodules, and thyroid cancer can be treated by partially or fully removing the thyroid gland. This may result in hypothyroidism.

Radiation treatment of the thyroid can also lead to hypothyroidism. Radioactive iodine is a common treatment for hyperthyroidism. It works by destroying the cells of the thyroid gland and decreasing the production of T4.

Radiation is also used to treat people with head and neck cancers, Hodgkin's disease, and other lymphomas, which can lead to damage of the thyroid gland.

Medication

A number of drugs can interfere with thyroid hormone production. These include amiodarone, interferon alpha, interleukin-2, lithium, and tyrosine kinase inhibitors.

Pituitary gland abnormalities

If the pituitary gland stops functioning properly, the thyroid gland may not produce the correct amount of thyroid hormone.

Pituitary tumors or pituitary surgery can affect the function of the pituitary gland, and this can adversely affect the thyroid gland.

Sheehan's syndrome is a condition that involves damage to the pituitary gland.

If a woman loses a life-threatening amount of blood or has severely low blood pressure during or after childbirth, the gland can be damaged, causing it to under-produce pituitary hormones.

Iodine imbalance

Iodine is needed for the production of the thyroid hormones, but the level must be balanced. Too much or too little iodine can lead to hypothyroidism or hyperthyroidism.

Some natural remedies are proposed for hypothyroidism, but it is important to speak to a doctor first, because the treatment for thyroid problems must be delicately balanced.

Selenium: People with some types of thyroid problem may benefit from taking selenium, but this should only be used after discussing it with a doctor. Researchers note that "either the deficiency or the excess of this micronutrient may be associated with adverse outcomes." Selenium supplements that are not recommended by a health professional could be hazardous.

Vitamin D: A deficiency has been linked with severity of disease in Hashimoto's. Supplementation may be necessary to reach beneficial vitamin D blood levels above 50 ng / dL.

Probiotics: Some people with hypothyroidism may have changes in the small intestine, where bacteria from the colon spread into the small intestine where they are not normally located, known as small intestine bacterial overgrowth (SIBO).

In one study, 40 patients had abnormal results on a glucose breath test. After taking the probiotic Bacillus clausii for one month, the test result for 19 participants was normal. Both antibiotics and probiotics have been shown effective for SIBO.

Additionally, for those with autoimmune and inflammatory thyroid conditions, supplements such as turmeric (containing at least 500 mg curcumin) and omega-3s may help to improve inflammation.

Doctors usually carry out a physical examination, take a medical history, and sent to a laboratory for analysis.

The most common blood test is the TSH test. This detects the amounts of TSH in the blood.

If the TSH reading is above normal, the patient may have hypothyroidism. If TSH levels are below normal, the patient may have hyperthyroidism or hypothyroidism.

The T3, T4, and thyroid autoantibody tests are additional blood tests used to confirm the diagnosis or determine its cause.

The doctor may run a complete thyroid panel, testing levels of T3 and T4, TSH, and thyroid autoantibodies in order to fully establish the health and activity of the thyroid gland.

There may also be tests to check cholesterol levels, liver enzymes, prolactin, and sodium.

Apart from some disorders and medications, other risk factors include:

People have a greater risk of developing a thyroid disorder if they have conditions such as Turner syndrome or autoimmune diseases like lupus or rheumatoid arthritis.

The risk of hypothyroidism is higher in people with a family history of thyroid disease and those aged over 60 years.

It most commonly affects women from middle age onward, but it can occur at any age.

During and after pregnancy

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Pregnancy can be a cause of hypothyroidism.

Increased demands on metabolism during pregnancy results in increased demands on the thyroid.

In one study, 85 percent of women who are pregnant and taking thyroid hormone replacement needed an additional intake of 47 percent on average, during pregnancy.

If hypothyroidism occurs during pregnancy, it is usually due to Hashimoto's disease. This condition affects between 3 and 5 out of every 1,000 women during pregnancy.

Uncontrolled hypothyroidism increases the risk of miscarriage, preterm delivery, and a rise in blood pressure during late pregnancy, or preeclampsia.

It can also affect brain development and growth rates.

Women who have been pregnant within the last 6 months have a higher risk of thyroiditis and hypothyroidism.