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).¹  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.

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)

Learn more about Hypothyroidism:

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.