<unk>  (also called underactive thyroid, low thyroid or hypothyreosis) is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. It can cause a number of symptoms, such as poor ability to tolerate cold, a feeling of tiredness, constipation, slow heart rate, depression, and weight gain. Occasionally there may be swelling of the front part of the neck due to goiter. Untreated cases of<unk>  during pregnancy can lead to delays in growth and intellectual development in the baby or congenital iodine deficiency syndrome. Worldwide, too little iodine in the diet is the most common cause of<unk> . Hashimoto's thyroiditis is the most common cause of<unk>  in countries with sufficient dietary iodine. Less common causes include previous treatment with radioactive iodine, injury to the hypothalamus or the anterior pituitary gland, certain medications, a lack of a functioning thyroid at birth, or previous thyroid surgery. The diagnosis of<unk> , when suspected, can be confirmed with blood tests measuring thyroid-stimulating hormone (TSH) and thyroxine levels. Salt iodization has prevented<unk>  in many populations. Thyroid hormone replacement with levothyroxine treats<unk> . Medical professionals adjust the dose according to symptoms and normalization of the thyroxine and TSH levels. Thyroid medication is safe in pregnancy. Although an adequate amount of dietary iodine is important, too much may worsen specific forms of<unk> . Worldwide about one billion people are estimated to be iodine-deficient; however, it is unknown how often this results in<unk> . In the United States,<unk>  occurs in 0.3–0.4% of people. Subclinical<unk> , a milder form of<unk>  characterized by normal thyroxine levels and an elevated TSH level, is thought to occur in 4.3–8.5% of people in the United States.<unk>  is more common in women than in men. People over the age of 60 are more commonly affected. Dogs are also known to develop<unk> , as are cats and horses, albeit more rarely. The word<unk>  is from Greek hypo- 'reduced', thyreos 'shield', and eidos 'form'.
Hypothyroidism
Heart failure
Late onset congenital adrenal hyperplasia
Dementia
Autoimmune thyroiditis
Depression (mood)
Acromegaly
Chronic fatigue syndrome