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Too little thyroid hormone. Symptoms include weight gain, constipation, dry skin, and sensitivity to the cold. Also called underactive thyroid.

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(Source: NIH - National Cancer Institute)

About Hypothyroidism

The thyroid gland performs a vital function: It produces the hormones that regulate the body's metabolism and keep them in balance. Thyroid hormones direct many of the body's processes.

An underactive thyroid does not produce enough hormones. This condition is also referred to as hypothyroidism. It slows down the metabolism, which may cause fatigue, lethargy, or constipation, but these kinds of symptoms can also have a number of other causes. An underactive thyroid can only be diagnosed by examining the level of thyroid hormones in the blood.

Chronic inflammation of the thyroid gland is the most common cause of an underactive thyroid... Read more about Hypothyroidism

What works? Research summarized

Evidence reviews

Radiation-induced hypothyroidism in head and neck cancer patients: a systematic review

PURPOSE: To review literature on the relationship between the dose distribution in the thyroid gland and the incidence of radiation-induced hypothyroidism in adults.

Subclinical hypothyroidism and the risk of coronary heart diesase and mortality

CONTEXT: Data regarding the association between subclinical hypothyroidism and cardiovascular disease outcomes are conflicting among large prospective cohort studies. This might reflect differences in participants' age, sex, thyroid-stimulating hormone (TSH) levels, or preexisting cardiovascular disease.

Risk of hypothyroidism following hemithyroidectomy: systematic review and meta-analysis of prognostic studies

This generally well-conducted review concluded that about 20% of patients develop low thyroid levels after removing half the thyroid gland; one in 25 have free thyroxine and thyroid stimulating hormone levels below normal. Uncertainty over the quality of the included studies and the diversity and limitations of the available evidence make the reliability of the conclusions uncertain.

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Summaries for consumers

Underactive thyroid: Deciding whether to treat subclinical hypothyroidism

Subclinical (latent) hypothyroidism means that the thyroid gland is still producing enough thyroid hormones. But some blood values may suggest the early stages of a hormone deficiency. Experts do not agree on whether subclinical hypothyroidism should be treated. It is not clear in which cases treatment would have advantages.If you already have noticeable (“overt” or “manifest”) hypothyroidism, the thyroid is no longer producing enough thyroid hormones. Thyroxine is the most important of the thyroid hormones. It helps regulate many of the body’s functions to balance your metabolism. Too little thyroxine can cause a number of different health problems. The symptoms range from cold hands to physical weakness, slower mental processes and depression. An underactive thyroid (hypothyroidism) is treated with hormone tablets that are taken once daily. These tablets act to replace the thyroxine that is not being produced. This can usually make the symptoms disappear completely.Subclinical hypothyroidism goes unnoticed. Only the body’s levels of TSH (“thyroid-stimulating hormone”) are too high. The thyroid is still producing enough thyroid hormones. The hormone TSH is produced in the pituitary gland and acts as a trigger for the thyroid to start producing the thyroid hormones. TSH levels that are just a little too high may be the first sign of the early stages of hypothyroidism: The pituitary gland responds to lower levels of thyroid hormones by increasing TSH production to activate the thyroid. It is also possible that TSH reaches higher levels only temporarily, for example after intense physical activity.It is estimated that about 5 out of 100 people have subclinical hypothyroidism. Slightly elevated TSH levels are usually detected by accident during a routine examination. But taken on their own they do not pose any health risk – often the effect is just temporary. Experts do not fully agree on how to decide in which cases subclinical hypothyroidism should be treated.

Chinese herbal medicines for hypothyroidism

Hypothyroidism, also known as underactive or low thyroid, is a condition in which the thyroid gland does not produce sufficient amounts of thyroid hormones which are important for many functions of the body (metabolism). In adults hypothyroidism may cause fatigue and sluggishness, increased sensitivity to cold, constipation, pale and dry skin, brittle fingernails and hair, a puffy face, hoarse voice, unexplained weight gain, muscle aches, tenderness, stiffness and weakness, pain, stiffness or swelling in the joints, heavier than normal menstrual periods, and depression. Hypothyroidism in infants and teenagers may result in poor growth and mental development as well as delayed development of permanent teeth and puberty.

High versus low dose of initial thyroid hormone replacement for congenital hypothyroidism

Congenital hypothyroidism is a condition that affects infants from birth and results from a missing or abnormally developed thyroid gland, abnormal production of thyroid hormones or a failure of the pituitary gland to stimulate thyroid hormone production. It affects approximately 1 in 3000 to 4000 newborn infants and early diagnosis and treatment is very important to achieve a good outcome.Treatment of congenital hypothyroidism consists of a daily dose of thyroid hormone (thyroxine). However, the initial dose of thyroxine required to improve outcomes for infants with this condition is unclear and has been the subject of several studies. Some studies have suggested that when infants with congenital hypothyroidism are treated with a higher dose of thyroxine compared with the standard dose, this results in earlier normalisation of the their thyroid hormones and leads to better developmental outcome and intelligence.

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Terms to know

The chemical changes that take place in a cell or an organism. These changes make energy and the materials cells and organisms need to grow, reproduce, and stay healthy. Metabolism also helps get rid of toxic substances.
Thyroid Gland
A gland located beneath the larynx (voice box) that makes thyroid hormone and calcitonin. The thyroid helps regulate growth and metabolism. Also called thyroid gland.
Thyroid Hormones
A hormone that affects heart rate, blood pressure, body temperature, and weight. Thyroid hormone is made by the thyroid gland and can also be made in the laboratory.
Thyroid-Stimulating Hormone (TSH)
A hormone produced by the pituitary gland. TSH stimulates the release of thyroid hormone.

More about Hypothyroidism

Photo of an adult woman

Also called: Underactive thyroid, Thyroid deficiency, Thyroid insufficiency

See Also: Hyperthyroidism

Other terms to know: See all 4
Metabolism, Thyroid Gland, Thyroid Hormones

Related articles:
Thyroid Function Tests

Keep up with systematic reviews on Hypothyroidism:


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