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Hypothyroidism is a condition in which the thyroid gland fails to function adequately, resulting in reduced levels of thyroid hormone in the body. Cretinism is a type of hypothyroidism that occurs at birth and results in stunted physical growth and mental development. Severe hypothyroidism is called myxedema.

There are many causes of hypothyroidism. Hashimoto's thyroiditis is an autoimmune disease of the thyroid gland and the second most common cause of hypothyroidism. The most common cause of hypothyroidism is medical treatment, such as surgery or radiation to the thyroid gland, to treat hyperthyroidism (over-activity of the thyroid gland). Some drugs, such as lithium and phenylbutazone, may also induce hypothyroidism. Extreme iodine deficiency, which is rare in the United States, is another possible cause. Failure of the pituitary gland or hypothalamus to stimulate the thyroid gland properly can cause a condition known as secondary hypothyroidism.

Some people with goiter (an enlargement of the thyroid gland) also have hypothyroidism. Goiter can be caused by an iodine deficiency, by eating foods that contain goitrogens (goiter-causing substances), or by other disorders that interfere with thyroid hormone production. In many cases the cause of goiter cannot be determined. While natural therapies may help to some extent, thyroid hormone replacement is necessary for most people with hypothyroidism.

What are the symptoms of hypothyroidism? The symptoms of hypothyroidism vary from person to person, but commonly include several of the following: fatigue, lethargy, intolerance to cold, constipation, weight gain, depression, excessive menstruation, dry skin, hair loss, and hoarseness. The onset of these symptoms may be so gradual as to evade detection by patient or physician.

Conventional treatment options: The preferred conventional treatment for hypothyroidism is the synthetic thyroid hormone levothyroxine (Synthroid®, Levothroid®, Levoxyl®).

Dietary changes that may be helpful: Some foods, such as rapeseed (used to make canola oil) and Brassica vegetables (cabbage, Brussels sprouts, broccoli, and cauliflower), contain natural goitrogens, chemicals that cause the thyroid gland to enlarge by interfering with thyroid hormone synthesis. Cooking has been reported to inactivate this effect in Brussels sprouts. Cassava, a starchy root that is the source of tapioca, has also been identified as a goitrogenic food. Other goitrogens include maize, sweet potatoes, lima beans, soy, and pearl millet. While some practitioners recommend that people with hypothyroidism avoid these foods, none has been proven to cause hypothyroidism in humans.

Lifestyle changes that may be helpful: Preliminary studies have found an association between multiple chemical sensitivities and hypothyroidism. One study found a correlation between high blood levels of lead, a toxic heavy metal, and low thyroid hormone levels in people working in a brass foundry. Many of these people also complained of depression, fatigue, constipation, and poor memory (symptoms of hypothyroidism).

Occupational exposure to polybrominated biphenyls and carbon disulfide has also been associated with decreased thyroid function.

Nutritional supplements that may be helpful: The relationship between iodine and thyroid function is complex. Iodine is required by the body to form thyroid hormone, and iodine deficiency can lead to goiter and hypothyroidism. Severe and prolonged iodine deficiency can potentially lead to serious types of hypothyroidism, such as myxedema or cretinism. It is estimated that one and a half billion people living in 118 countries around the world are at risk for developing iodine deficiency.

Today, most cases of iodine deficiency occur in developing nations. In industrialized countries where iodized salt is used, iodine deficiency has become extremely rare. On the other hand, iodine toxicity has become a concern in some of these countries. Excessive iodine intake can result in either hypothyroidism or hyperthyroidism (overactive thyroid). Sources of iodine include foods (iodized salt, milk, water, seaweed, ground beef), dietary supplements (multiple vitamin-mineral formulas, seaweed extracts), drugs (potassium iodide, amiodarone, topical antiseptics), and iodine-containing solutions used in certain laboratory tests. Many nutritional supplements contain 150 mcg of iodine. While that amount of iodine should prevent a deficiency, it is not clear whether supplementing with iodine is necessary or desirable for most people. Those wishing to take a nutritional supplement containing iodine should consult a doctor.

Laboratory animals with severe, experimentally induced zinc deficiency developed hypothyroidism, whereas moderate zinc deficiency did not affect thyroid function. In a small study of healthy people, thyroid hormone (thyroxine) levels tended to be lower in those with lower blood levels of zinc. In people with low zinc, supplementing with zinc increased thyroxine levels. One case has been reported of a woman with severe zinc deficiency (caused by the combination of alcoholism and malabsorption) who developed hypothyroidism that was corrected by supplementing with zinc. Although the typical Western diet is marginally low in zinc, additional research is needed to determine whether zinc supplementation would be effective for preventing or correcting hypothyroidism.

Selenium plays a role in thyroid hormone metabolism. Severe selenium deficiency has been implicated as a possible cause of goiter. Two months of selenium supplementation in people who were deficient in both selenium and iodine was shown to induce a dramatic fall of the already impaired thyroid function in clinically hypothyroid subjects. Researchers have suggested that people who are deficient in both selenium and iodine should not take selenium supplements without first receiving iodine or thyroid hormone supplementation. There is no research demonstrating that selenium supplementation helps people with hypothyroidism who are not selenium-deficient.

Preliminary data indicate that vitamin B3 (niacin) supplementation may decrease thyroid hormone levels. In one small study, 2.6 grams of niacin per day helped lower blood fat levels. After a year or more, thyroid hormone levels had fallen significantly in each person, although none experienced symptoms of hypothyroidism. In another case report, thyroid hormone levels decreased in two people who were taking niacin for high cholesterol and triglycerides; one of these two was diagnosed with hypothyroidism. When the niacin was discontinued for one month, thyroid hormone levels returned to normal.

Desiccated thyroid, also called thyroid extract (e.g., Armour Thyroid), is used by some doctors as an alternative to synthetic thyroid hormones (such as thyroxine [Synthroid® or other brand names]) for people with hypothyroidism. Thyroid extract contains two biologically active hormones (thyroxine and triiodothyronine), whereas the most commonly prescribed thyroid-hormone preparations contain only thyroxine. One study has shown that the combination of the two hormones contained in desiccated thyroid is more effective than thyroxine alone for those with hypothyroidism. One doctor reported that thyroid extract worked better than standard thyroid preparations for many of his patients with hypothyroidism. Glandular thyroid products, which are available from health food stores, have had most of the thyroid hormone removed and would therefore not be expected to be effective for people with hypothyroidism. Intact desiccated thyroid is available only by prescription. Hypothyroidism sufferers who want to use desiccated thyroid must first consult with a physician.

People with hypothyroidism have been shown to have an impaired ability to convert beta-carotene to vitamin A.For this reason, some doctors suggest taking supplemental vitamin A (approximately 5,000–10,000 IU per day) if they are not consuming adequate amounts in their diet.

Are there any side effects or interactions? Refer to the individual supplement for information about any side effects or interactions.

Herbs that may be helpful: Bladderwrack (Fucus vesiculosus) is a type of brown seaweed that contains variable amounts of iodine. Hypothyroidism due to insufficient intake of iodine may possibly improve with bladderwrack supplementation, though human studies have not confirmed this.

Some Chinese herb formulations show promise for people with hypothyroidism. In one study, people with hypothyroidism were given a combination of Chinese herbs. After one year, symptoms of hypothyroidism were markedly improved and blood levels of thyroid hormones had significantly increased. In an animal study, administration of certain Chinese herbs raised thyroid hormone levels in the blood. Neither study listed the specific herbs used. People with hypothyroidism who wish to use Chinese herbs should consult with a physician skilled in their use.

Are there any side effects or interactions? Refer to the individual herb for information about any side effects or interactions.