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Thyroid Disease
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The American Association of Clinical Endocrinologists (AACE) is the country's largest professional organization of clinical endocrinologists. The association strives to improve the public's understanding and awareness of endocrine diseases and the added value of the clinical endocrinologist in the diagnosis and treatment of these diseases. The site includes an easy-to-use search tool enabling you to find an endocrinologist in your area.
AARDA is a national nonprofit health agency dedicated to bringing a national focus to autoimmunity. The association supports a nationwide 800 telephone referral line which provides information and referral services to thousands of inquirers annually. The site includes an extensive section for consumers about autoimmune disease
The ATA is a professional society of 900 U.S. and international physicians and scientists who specialize in the research and treatment of thyroid diseases. The site includes web brochures on each thyroid disorder and an easy-to-use search tool enabling you to find an endocrinologist in your area.
The Hormone Foundation is the public education affiliate of The Endocrine Society, an international body with 14,000 members from over 100 countries. The site provides hormone-related health information to the public, physicians, allied health professionals and the media.
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When the thyroid gland loses its ability to make thyroid hormone, a person's whole life can be turned upside down.  Affecting the physical and mental well-being of a person, the proper treatment of hypothyroidism can make a remarkable difference to overall health.

Gaining weight?  Feeling fatigued?  Down in the dumps?  These can all be symptoms of thyroid disease.  Hypothyroidism is more common than you may believe.  Depending on the diagnostic criteria used, hypothyroidism could be affecting anywhere between 5% and 10% of the population.  Many people may have this disease and not even realize it.  According to a study known as the Colorado Thyroid Disease Prevalence Study there may be as many as 13 million Americans with an undiagnosed thyroid condition.

What is Thyroid Disease?

To understand thyroid disease, you need to know a little bit about the thyroid gland, an important part of your endocrine system. The thyroid gland is one of the largest endocrine glands.  Dysfunction and distortion of the thyroid gland are among the most common of the endocrine system problems.  Its two lobes look a bit like a butterfly with a "wing" or lobe on each side of your windpipe in the front of your neck connected by a small band of tissue called an isthmus. At just a little over an ounce and a couple of inches side-to-side, it is small but it has a big job.  The thyroid gland has several functions: it forms thyroglobulin, a binding protein; traps, concentrates, and processes iodine; synthesizes and stores thyroid hormone; and releases the hormone as the body needs it. Thyroid hormone helps regulate processes like metabolism (the breakdown of food and its transformation into energy), your body temperature, your heart rate, your blood pressure, and more.  The thyroid gland also secretes thyrocalcitonin, which stimulates the movement of calcium from the bloodstream to the bones.   

Types of Thyroid Disease

An over producing ("hyper") or under producing ("hypo") thyroid impacts every part of your body, including your heart and your brain.  

  • Hyperthyroidism:  Excessive amounts of thyroid hormones accelerate body functions and can lead to swelling in the neck (goiter), an increased heart rate or palpitations, anxiety and irritability, tremors, muscle weakness, thinning of the skin, hair loss, osteoporosis, heat intolerance, difficulty sleeping, shorter and lighter menstrual periods, and weight loss despite a strong appetite.
  • Hypothyroidism:  If thyroid hormone levels are too low, body functions can slow down and lead to swelling in the neck (goiter), a slow heart rate, an increase in LDL cholesterol levels, mild anemia, pervasive fatigue, depression, slowed mental functioning, sluggish reflexes, reduced body temperature, cold intolerance, drying and coarsening of the skin, muscle and joint aches, constipation, weight gain in spite of reduced appetite (though only in the range of 5 to 10 pounds), fluid retention, increased sensitivity to many medications, lower libido and other problems with the reproductive system including infertility, increased risk of miscarriage and heavy or irregular menstrual flow in women and erectile dysfunction in men, low sperm count, slow wound healing, easy bruising, slowed hair growth, obstructive sleep apnea, constipation, gas distension of the abdomen, stiff aching muscles worsened by cold.

The most common form of thyroid disease is hypothyroidism (also called underactive thyroid disease).  99% of hypothyroidism is due to a permanent loss of the thyroid gland's ability to make enough thyroid hormone and is known as primary hypothyroidism.  Other reasons for hypothyroidism, transient or permanent, are rare.  Diagnosis is done with simple blood tests but there are some wrinkles.  The symptoms of hypothyroidism may appear gradually, often over months or years, making them easy to overlook by the patient, family, and friends.  They can also mimic other conditions, especially those normally associated with menopause and advancing age.  Finally, there are no commonly accepted guidelines for screening.  Because women are 5 to 8 times more likely than men to suffer from a thyroid condition1 and its incidence increases with age, the American College of Physicians (ACP) recommends hypothyroid screening for women over 50.  The American Thyroid Association recommends screening for women every five years beginning at age 35.  Many doctors recommend automatic screening for pregnant women or women thinking of becoming pregnant and annual checks for people with a family history of autoimmune disease.

Once hypothyroidism is diagnosed, treatment by replacing the missing thyroid hormone is usually very successful.  It can be a long process to establish the proper dosage, but once that's achieved, patients generally begin to feel like they did before becoming hypothyroid. 

1 Wood L.C. "Your Thyroid: A Home Reference," Ballantine Books, New York, 1995 (pp. 216-217).


Quick Facts

  • Hyperthyroidism, which is a condition marked by an abnormally high level of thyroid hormones in the blood.
  • Hypothyroidism is a disorder in which the thyroid gland does not produce enough thyroid hormone to meet the body's needs.
  • The most common cause of hypothyroidism in the United States is a disease called Hashimoto's thyroiditis. This is an autoimmune disorder in which the body's immune system attacks and inflames the thyroid gland.
  • More than eight out of 10 patients with thyroid disease are women.
  • Nearly one out of 50 women in the United States is diagnosed with hypothyroidism during pregnancy.
  • Six out of every 100 miscarriages are associated with thyroid hormone deficiencies during pregnancy.
  • One out of every four thousand babies born in the United States has hypothyroidism.
  • Incidence of hypothyroidism increases with age.
  • You have a higher risk of developing thyroid disease if, among a variety of factors:
    • You have a family member with a thyroid problem
    • You have another pituitary or endocrine disease
    • You or a family member have another autoimmune disease
    • You've been diagnosed with Chronic Fatigue Syndrome
    • You've been diagnosed with Fibromyalgia
    • You're female
    • You're over 60
    • You've had early graying of scalp hair (before the age of 30)
    • You've just had a baby
    • You're near menopause or menopausal
    • You're a smoker
    • You've been exposed to radiation
    • You've been treated with lithium
    • You've been exposed to certain chemicals (i.e., perchlorate, fluoride)
  • The thyroid gland produces hormones that influence essentially every organ, tissue and cell in the body.
  • Common symptoms of hyperthyroidism are swelling in the neck (goiter), an increased heart rate or palpitations, anxiety and irritability, tremors, muscle weakness, thinning of the skin, hair loss, osteoporosis, heat intolerance, difficulty sleeping, shorter and lighter menstrual periods, and weight loss despite a strong appetite.
  • Common symptoms of hypothyroidism are swelling in the neck (goiter), a slow heart rate, an increase in total cholesterol levels, anemia, pervasive fatigue, depression, slowed mental functioning including poor concentration and memory, sluggish reflexes, cold intolerance, drying and coarsening of the skin, muscle and joint aches, constipation, weight gain and fluid retention, increased sensitivity to many medications, lower libido and other problems with the reproductive system including infertility, increased risk of miscarriage and heavy or irregular menstrual flow in women and erectile dysfunction in men.
  • Because the range of symptoms in hypothyroidism is so wide, it can be difficult for doctors to diagnose.
  • Hypothyroidism is generally diagnosed with blood tests.
  • The majority of people with hypothyroidism will need to take manufactured versions of natural thyroid hormones for the rest of their lives to relieve their symptoms and to avoid serious long-term consequences.
  • A dose of thyroid hormone that is too low may fail to prevent enlargement of the thyroid gland, allow symptoms of hypothyroidism to persist, and be associated with increased serum cholesterol levels, which may increase the risk for atherosclerosis and heart disease. A dose that is too high can cause symptoms of hyperthyroidism, create excessive strain on the heart, and lead to an increased risk of developing osteoporosis.

These quick facts have been adapted from information from the American Association of Clinical Endocrinologists


Ask Your Doctor

  • What is my risk for thyroid disease?
  • Is there anything I can do to reduce my risk?
  • Do I need a TSH screening test, even though I don't have thyroid disease symptoms? 
  • I've noticed these symptoms:  . . . Do I need a TSH screening test?
  • What TSH level will you use as a target for me?
  • Do all individuals fit into the "normal" range for TSH levels? 
  • If a test shows you have subclinical hypthyroiditis... What is your position about treating someone with subclinical hypothyroiditis?
  • What sorts of symptoms should I be watching for?
  • What caused my hypothyroidism?
  • Should I be referred to a specialist?
  • Can I take thyroid replacement hormone if I am pregnant or trying to get pregnant?
  • What thyroid hormone replacement drug are you going to prescribe for me?
  • How quickly can we expect my TSH to return to normal?
  • How often will you test my TSH until we get it back into the normal range?
  • Is my condition permanent?  Is it likely to get progressively worse?
  • After I am in the normal range, how often will I need a TSH test to make sure my dosage needs have not changed?

Key Point 1

The thyroid gland is a critical part of your body's regulatory system and affects your physical and mental health.  Symptoms caused by too little or too much thyroid hormone can greatly affect your daily life. 

Small but mighty – that is your thyroid gland.  Untreated thyroid disease can wreak havoc with your entire body.  Read the introductory page for this topic for an overview of what your thyroid does and the symptoms of the two most common thyroid disorders – hyperthyroidism and hypothyroidism.  

Eighty percent of patients diagnosed with thyroid disease have hypothyroidism (underactive thyroid).Anyone can develop hypothyroidism, though it is most prevalent in women over 50 years old. 

  • Hypothyroidism in infants:   A non-functioning thyroid gland affects 1 in 4,000 newborns.2 Left untreated, even mild cases can cause difficulties in physical, neurologic and mental development.  All states screen for hypothyroidism as part of their standard newborn blood screening programs3 to prevent permanent mental retardation.
  • Hypothyroidism in children and teens:  When hypothyroidism develops in children over 2 years of age, permanent mental retardation is no longer a danger.  However, depending on its severity, the disease may slow growth in height, delay development of permanent teeth, cause attention problems and delay sexual development.  Children and teens may also exhibit the same symptoms as adults (see our introductory page for this topic for a list of common symptoms).
  • Hypothyroidism in women of childbearing age: Approximately one in 100 women of childbearing age has hypothyroidism.4 Because thyroid hormones play an essential part in normal brain development and the fetus relies on the mother for thyroid hormones during the first few months of pregnancy, children born to mothers with untreated hypothyroidism are more likely to have serious intellectual and developmental problems.5  Women should be tested for a thyroid disorder before becoming pregnant and every 6 to 8 weeks during pregnancy.
  • Hypothyroidism in adult men and women:  About 10 percent of women and 3 percent of men have hypothyroidism, according to the American Association of Clinical Endocrinologists.  That increases to as many as 17 percent of women and 10 percent of men after age 60.  See the symptoms outlined on our introductory page for this topic.

Symptoms of Hypothyroidism

No two people present exactly the same symptoms.  In fact, the effects of hypothyroidism can vary greatly from subclinical (where the individual is asymptomatic but a blood test indicates low thyroid function) to a rare but life threatening hypothyroidism known as myxedema.

While many of the symptoms of hypothyroidism are simply distressful, others can be dangerous.  Hypothyroidism may:

  • Raise levels of total cholesterol, LDL ("bad" cholesterol), which is associated with heart disease and stroke.  The total elevation is about 10%, and that much elevation goes away when the hypothyroidism is treated.  HDL and triglyceride levels are unchanged.
  • Increase your risk of developing hypertension
  • Increase the risk of heart failure in people with existing heart disease (Hypothyroidism is associated with reduced stroke volume, reduced heart rate, increased peripheral resistance, and reduced blood volume.  Therefore, the individuals have cool, pale skin.  But in contrast to congestive heart failure, with exercise the stroke volume improves and the peripheral resistance goes down in hypothyroidism.) 
  • Result in depression, sometimes severe, sometimes with agitation.
  • Cause mental and behavioral impairment including dementia and what has been known as "slow-witted".
  • Increase your risk for glaucoma
  • Cause respiratory problems, mainly obstructive sleep apnea and reduced maximal breathing capacity
  • Increase your risk for diminished libido, sexual dysfunction, infertility or miscarriage

Endocrinologists recommend that men and women ask their health care provider to check their thyroid as part of their routine health care.

1 Hollowell JG, Staehling NW, Flanders WD, Hannon WH, Gunter EW, Spencer CA, Braverman LE 2002 Serum TSH, T4, and thyroid antibodies in the United States population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III). J Clin Endocrinol Metab 87:489–499.
2 Congenital Hypothyroidism, Daniel C Postellon, MD, Clinical Associate Professor, College of Human Medicine, Pediatrics and Human Development, Michigan State University.
3 The National Newborn Screening & Genetics Resource Center.
4 The Endocrine Society.
5 New England Journal of Medicine.
6 Wood L.C. "Your Thyroid: A Home Reference," Ballantine Books, New York, 1995 (pp. 216-217)

Key Point 2

Hypothyroidism is treated by replacing the thyroid hormone that the body is not producing.  Untreated hypothyroidism and over-treated hypothyroidism can be harmful. 

There are three types of hypothyroidism:

  • Primary hypothyroidism occurs when the thyroid gland fails to produce thyroxine (T-4) and triiodothyronine (T-3).
  • Secondary hypothyroidism occurs when the pituitary fails to secrete adequate thyroid-stimulating hormone (also known as TSH or thyrotropin).
  • Tertiary hypothyroidism occurs when the hypothalamus fails to deliver thyrotropin releasing-hormone (TRH) to the pituitary gland.

Primary hypothyroidism accounts for over 99 percent of cases. Primary hypothyroidism may be the end result of:

  • Hashimoto's thyroiditis (an autoimmune disease where the body produces antibodies that attack and damage the thyroid)
  • Complications of thyroid surgery or surgical removal of the thyroid
  • Radioiodine therapy or anti-thyroid medications to treat hyperthyroidism
  • Radiation used to treat cancers of the head and neck
  • Certain types of thyroid inflammation or viral infections
  • Certain medications, such as lithium (used to treat certain psychiatric disorders)
  • A congenital thyroid defect (occurs in 1 in 4,000 babies)
  • Postpartum thyroiditis that causes the thyroid to go through a period of hyperthyroidism followed by a period of hypothyroidism
  • Iodine deficiency.  (This is a problem in some parts of the world but not in the U.S. because of our use of iodized salt.)

Primary hypothyroidism can also occur for no apparent reason (called spontaneous onset).

Diagnosis of primary hypothyroidism is based on characteristic symptoms and physical signs and the results of blood tests that measure your level of thyroid-stimulating hormone (TSH) and sometimes your level of the thyroid hormone thyroxine (T4). A low level of thyroxine and high level of TSH indicate an underactive thyroid. That is because your pituitary produces more TSH in an effort to stimulate your thyroid gland into producing more thyroid hormone.1   The most commonly used test is the measurement of thyroid-stimulating hormone (TSH).  What is considered normal?   Traditionally, a TSH value of less than 0.5 was considered hyperthyroid (overactive thyroid), while a TSH value of more than 5.5 was considered hypothyroid (underactive thyroid).  In 2002 the American Association of Clinical Endocrinologists (AACE) recommended a narrower TSH reference range of 0.3 to 3.0.  Ask your doctor what values your lab uses.

Your doctor may order other tests to determine the cause of your hypothyroidism, including one for thyroid autoantibodies to identify autoimmune thyroiditis (Hashimoto's thyroiditis) or imaging tests such as ultrasound or radioactive scanning  to look for physical and functional abnormalities.    

The American Association of Clinical Endocrinologists (AACE) also recommends that people routinely perform a simple self-examination called the Neck Check™.  Go to
 for step-by-step instructions.    

The goal of treatment for hypothyroidism is to bring your thyroxine (T4) level back into balance and achieve a TSH level between the AACE reference range of 0.3 to 3.0.  A synthetic hormone called levothyroxine (brand names include Levothroid, Levoxyl, Synthroid, and Unithroid) is standard.  Your doctor will choose the dosage based on your age, weight and any co-existing medical conditions and other medications or supplements you may be taking.  The dose of thyroid hormone is based upon lean body mass, not total body weight.  Doctors tend to ask patients remain on the same brand of thyroid hormone because even minor variations of equivalency brand to brand may have a significant impact.

It can take several weeks for your hypothyroid symptoms to improve after you start taking thyroid hormone medicine. You will need to keep track of your symptoms and be alert to any signs of over-replacement or under-replacement. Read the introductory page for this topic for an overview of hyperthyroidism and hypothyroidism symptoms.  Your doctor will have your TSH levels tested periodically to get to the dosage that is right for you.  It can be a long process for some.  Issues that can interfere include inconsistency in how you take your levothyroxine (it should be the same time every day an on an empty stomach to maximize absorption), missed doses, other medications, supplements or certain foods that may interfere with absorption, changes in estrogen levels (if you are approaching menopause) and changes in brand. 

Since most cases of hypothyroidism are permanent and often progressive, your doctor will continue routine checks on your TSH levels throughout your life. In general, we need about 20% less thyroid hormone by the time we are in our 70's and older.  With careful management, people with hypothyroidism can live healthy, normal lives.

Medline Plus

Medline Description: 

Conduct an off-site search for Hypothyroidism information from MedlinePlus.  These up-to-date search results are based on search terms specific to Second Opinion Key Points.

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