Thyroid Hormones - the basics
Thyroid hormones are essential in maintaining and regulating the body's metabolism. T3 is the most active of the thyroid hormones. Approximately 85% of circulating T3 is produced by mono deiodination of T4 - the inactive thyroid hormone in tissues such as the liver, muscle and kidney. This process of turning T4 into T3 requires selenium and zinc. TSH (Thyroid Stimulating Hormone) is a pituitary hormone that signals the thyroid to produce more or less thyroid hormones, depending on circumstances.
When things go wrong
Hyperthyroidism, or excess thyroid hormone, promotes a hypermetabolic state characterized by increased resting energy expenditure, weight loss, reduced cholesterol levels, increased lipolysis, and gluconeogenesis. Conversely, hypothyroidism, or reduced thyroid hormone levels, is associated with hypometabolism characterized by reduced resting energy expenditure, weight gain, increased cholesterol levels, reduced lipolysis, and reduced gluconeogenesis. Fatigue, poor sleep and inability to lose weight are often the presenting symptoms.
Reverse T3 (rT3) is an inactive form of T3 that is produced in the body particularly during periods of stress. Under normal conditions T4 will convert to both T3 and rT3 continually and the body eliminates rT3 quickly. Under certain conditions, more rT3 is produced and the desirable conversion of T4 to T3 decreases. This occurs during fasting, starvation, illness and during times of increased stress.
This becomes a vicious cycle as rT3 competes with T3. This inhibits the conversion of T4 to the active T3, with more T4 being converted to more rT3. This leaves the person feeling fatigued and with symptoms of hypothyroidism even though their thyroid is still functioning normally. TSH is often normal also.
Reverse T3 may be high due to:
- Increased Cortisol and other stressors
- Starvation or excessive dieting
- Increased Adrenalin
- Wilson's Thyroid Syndrome (excessive production of rT3 from T4)
- Euthyroid Sick Syndrome (Low circulating T3 levels despite normal gland function)
- Common in Chronic Fatigue Syndrome (CFS) and fibromyalgia
- Decreased levels of Selenium
Is high Reverse T3 an adaptive response?
When a person is chronically ill such as those with chronic fatigue or fibromyalgia the reverse T3 levels are often high. When a person is critically ill the same thing happens. Acute or chronic stress can show similar responses. If we consider the symptoms of high reverse T3 – basically the person wishes to sleep, hibernate, withdraw as they feel so fatigued, this can be seen as the body responding by protecting itself from further attack & retreating. If that analogy seems war like – it is, for some it feels like their body is fighting a war with itself.
Should we treat high Reverse T3?
That is a tricky one & understanding the reasons why the body is behaving in this way may be useful.
- If the cause is acute illness, the levels will often resolve once the illness is over. Selenium may help in this case. Selenium deficiency is more common in illness such as sepsis.
- If the cause is chronic illness, consider trying to address the underlying cause. Is that unresolved infection such as Shingles, EBV, Ross River Virus, SIBO (small intestinal bacterial overgrowth), h. Pylori infection etc?
- Is stress the major driver – it often is. The body is trying to protect you from all that stress as if you are this stressed something awful must be impending like being chased by a lion or a tiger - not that you have a work presentation or a deadline due…
So instead of trying to treat high Reverse T3. It is perhaps better to understand why the T3 is reduced and why there is an increase of Reverse T3. Why is the body trying to make you slow down, rest and recover? This is how we feel when we are unwell with a flu like illness. We want to go to bed and sleep it off. If we continue to soldier on as many of us do, we run the risk of falling in a heap & having T3 hormones that are inactive in the body long term rather than a short-term adaptive response. Taking jump leads to jump start the thyroid with high dose nutrients/ herbs / medications is not necessarily a good thing. Considering what your body is trying to protect you FROM & treating that will give better, long term results.
Economidou F, Douka E, Tzanela M, Nanas S, Kotanidou A. Thyroid function during critical illness. Hormones (Athens). 2011;10(2):117-124. doi:10.14310/horm.2002.1301
Mullur R, Liu YY, Brent GA. Thyroid hormone regulation of metabolism. Physiol Rev. 2014;94(2):355-382. doi:10.1152/physrev.00030.2013