The thyroid gland produces the hormones T3 (triiodothyronine) and T4 (thyroxine), which regulate metabolism and have an influence on nearly every cell in the body.  If the thyroid produces too much T3 or T4, then the consequence is an over-active metabolism that is disruptive to the entire body.  

The common signs and symptoms that can be a warning of an overactive thyroid include the following:

  • Weight loss that can’t be explained by a change in diet or activity level  
  • Rapid or irregular heart rate (often over 100 beats per minute)
  • Nervousness, anxiety, irritability, mood swings
  • Sweating that is out of place or excessive
  • Sensitivity to heat
  • Fatigue or muscle weakness 
  • Shaking (tremors) in the hands or fingers 
  • Increased frequency of bowel movements 
  • Difficulty sleeping
  • Thinning of skin, hair, nails 
  • Changes in the menstrual cycle, especially lighter or less frequent  

How common is overactive thyroid?

  • Hyperthyroidism affects 1.2% of the U.S. population.
  • Women are more likely to have an overactive thyroid than men.
  • The incidence of overactive thyroid increases with age.
  • The incidence of overactive thyroid increases during or shortly after pregnancy. 
  • Age has an effect on the way signs and symptoms appear.  
  • A diet high in iodine, over-use of iodine-containing supplements, and certain medications can increase risk for an overactive thyroid.
  • A family history of thyroid disease increases risk.1
  • Having an autoimmune disease (like rheumatoid arthritis) can increase risk.2

What can cause an overactive thyroid? 

In normal situations, the amount of T3 and T4 hormones produced by the thyroid is regulated by the amount of another hormone, TSH (thyroid stimulating hormone), which is produced in the brain.

When everything is working properly:

(1) Higher levels of TSH cause the thyroid to make T3 and T4.  This process involves an enzyme called TPO (thyroid peroxidase).

(2) As more T3 and T4 enter the bloodstream.

(3) TSH levels drop and production slows,

(4) Eventually thyroid hormone levels fall, becoming low enough to again trigger the release of TSH.

This cycle continues to repeat, keeping thyroid hormone levels from becoming too high or too low.

Anything that disrupts or bypasses this cycle and causes the uncontrolled production of thyroid hormones can lead to higher than normal levels of T3 and, more often, T4.  The most common causes of long-term overactive thyroid are: 

  • The presence of antibodies that recognize the thyroid and cause it to produce an excessive quantity of hormones 
  • Abnormal masses, usually non-cancerous, that grow in the thyroid and produce extra thyroid hormone 

Other instances of abnormally high levels of thyroid hormones can be temporary.  The most common of these instances occur from: 

  • Inflammation of the thyroid gland, causing it to produce more or to leak stored thyroid hormone.  This is often due to an infection, such as from a virus, but the specific trigger is not always known.  
  • Pregnancy, typically occurring within 6-12 months following delivery.  
  • Incorrect dosing of a drug, including synthetic thyroid hormones to treat low thyroid hormone levels. 
  • Excessive intake of iodine from the diet (such as from kelp or iodized salt) or medications (such as a cough medicine with an expectorant).3 

Many temporary cases of overproduction of thyroid hormone are followed by a period of abnormally low thyroid hormone levels before returning to normal.  

Consequences of overactive thyroid

Not every individual with high levels of T3 or T4 experiences obvious symptoms.  Certain medications (especially beta blockers) can mask some symptoms.  Changes often develop slowly over time making it easy to overlook them.  Many of the signs and symptoms of overactive thyroid are very similar to those from other causes, making it easy to explain them away.  For example, stress can also cause mood swings and fatigue and caffeine can make the heart race and the hands shake.  

A lack of obvious signs and symptoms does not mean there is no damage being done. Overactive thyroid, if untreated, can have serious consequences for the: 

  • Heart – blood clots, stroke, heart failure 
  • Bones – osteoporosis 
  • Eyes – inflammation around the eyes can affect vision 
  • Psychological well-being – many symptoms are distressing and can reduce quality of life, especially in older patients whose condition could be mistaken for depression or dementia

Testing – Knowing is half the battle

The most reliable way to detect overactive thyroid is through a blood test that measures T3 and T4 thyroid hormone levels.  Testing for TSH levels and the presence of TPO antibodies (which interfere with TPO function) can help pinpoint the cause of a detected imbalance or signal the need for closer monitoring due to increased risk.  

The at-home Thyroid Test from Thorne measures all four of the biomarkers described above (T3, T4, TSH, and TPO antibodies) and makes it easy to monitor your thyroid health anytime.  Collecting a sample for this test is quick and easy and can be done from the comfort and privacy of home.  With the power of reliable and easy to understand data in hand, you and your health-care practitioner can make informed decisions about the course of action that is best suited to your individual needs; helping you to be your healthiest you.

Many circumstances can cause unexplained weight loss or the other indicators of overactive thyroid. It can be difficult to determine what the culprit is or how best to address a problem.  And, while testing is an important tool, it does not replace your health-care practitioner’s expertise and guidance.  Therefore, it is important to consult a health-care practitioner if you suspect a problem with your thyroid gland or if you are experiencing signs or symptoms even when you have normal thyroid test results.


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