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Reverse T3 and the Body Preventing Weight Loss, on Purpose

We have highlighted many times the powerful role that hormones play in controlling weight loss, especially the thyroid hormone.  So often, when we are trying to support patients with weight loss, we are focused on minor factors and missing the significant impact of hormones.

There were many excellent follow-up questions from practitioners about thyroid labwork and about Reverse T3 (RT3) in particular.  The ubiquitous “TSH alone” labwork approach that many conventional practitioners use can hide many (most!?) thyroid hormone imbalances.  We can instead educate our clients about this potential missed opportunity and recommend they pursue a full thyroid panel, including at least TSH, Free T4, Free T3, TPO and Tg autoantibodies, and Reverse T3.

thyroid-glandFirst of all, let’s bust some myths.  Contrary to many online rants, Reverse T3 is not a “toxic” substance or one that is only produced during times of stress; your body is making it all the time.  The thyroid gland makes both the active T3 (to serve its own needs and to send some out into the body) and the T4 thyroid hormone as our metabolic reserve.  As needed, some peripheral tissues (esp. liver, kidneys) convert T4 into RT3 or T3 not only for their local use but also for systemic support (primarily via the D1 deiodinase enzyme) that is reflected in bloodwork.  However, each cell also has the ability to carry out localized intracellular T4-to-T3  conversion (via the D2 deiodinase enzyme).  Intracellular T3 drives our metabolism.

The concern is when too much of our T4 supply is being converted to Reverse T3 and leaving an inadequate amount for T3 synthesis to drive cellular effects.  Generally, this is at play when either an individual has excessive T4 (e.g. Graves disease or taking excessive prescription T4) or when the body is in a state of stress/trauma/disease.  The former is an often overlooked gotcha with the traditional T4-only medication for hypothyroidism.  The latter is a commonly overlooked aspect of physiology where excessive activity of the D3 deiodinase enzyme is not only creating excessive Reverse T3 (thus deactivating T4) but is also overtly deactivating T3 (and thus making less of it available for cellular effects).  It is actually the activity of this D3 deactivating enzyme that is to blame for this particular type of thyroid hormone imbalance and the resulting hypothyroid state. 

Contrary to common understanding (even in the functional medicine world!), Reverse T3 does not fit into cellular nuclear receptors and somehow maker fewer available for free T3.  There is much misunderstanding perpetuated about this topic; this article may be a great place to start in gaining some clarity.

High activity of the D3 deiodinase is likely how the body has evolved to conserve energy and protects tissue in times of disease or stress, in order to ensure our survival. Remember always that we have primal mechanisms at play to prioritize surviving over thriving.  If we want the body to allow the thriving implicit in weight loss and lighter weight maintenance, we have to convince the body that our survival is not being threatened….convince the body that all is well both inside and out.  Many mechanisms of inflammation may increase the activity of D3, leading to lower levels of available T3 (with or without high levels of Reverse T3)!

This is where becoming proficient in identifying the interconnectedness of each unique person’s challenges is critical (and why we have made it a strong focus and particular strength of SAFM programs!).  Sometimes the drivers for sustained, high stress are mental/emotional (e.g., ugly divorce, overwhelming work demands).  However, there are also often physiological sources of stress at play e.g.  unacknowledged food sensitivities, persistent simmering infections (e.g., high viral load, recurrent yeast overgrowth), toxicity (e.g., heavy metals such as mercury), use of beta-blocker drugs, or an ongoing source of inflammation (e.g., unacknowledged prediabetes).  Ultimately, these patients must partner with savvy practitioners in order to address the true root cause of their unique challenges in order to find lasting relief.

With gratitude to you for sharing your gifts with the world,

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*** Calculating this ratio can be confusing to practitioners and patients alike if “math isn’t your thing.”  If FT3 is measured in pg/dl (e.g., 320), and RT3 is measured in mg/dl (e.g., 15), then the target ratio is indeed 20 or higher.  If FT3 is in ng/ml (e.g., 3.2) and RT3 is still in mg/dl (e.g., 15), the target ratio would be 0.2 or higher.  If you do the math, however, and actually convert the numbers to the same units (as any good scientist will demand!), then the target ratio is actually 0.02.  The geek in me insists on clarifying this to make it entirely accurate 🙂  There are many helpful tools online to help you explore accurate conversions yourself.

 

P.S.  If you are passionate about transforming healthcare through the power of functional medicine, we encourage you to learn more about our training program here.

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Lisa
Lisa

I am really struggling with the math, it just doesn’t look right.
fT3 3.31 pg/ml
rT3 0.30 ng/ml
I converted the ng/ml ~ pg/ml = 300 pg/ml
Ratio 1.1
Is this correct as it seems very low. I would be grateful for any help in this matter

SAFM Team
Reply to  Lisa

Your conversion of the units is correct however the ratio that you calculated is not. In this case, it is calculated as fT3/rT3, this 3.31/300 = 0.011, which is not exactly at the optimal target of 0.2 – please note the *** at the bottom of the article for more explanation – but not that far off.

Lisa Zielbauer
Lisa Zielbauer

Thank you for the explanation Tracy. I went through and applied everything you said to my patient. My question is if the patient has normal/suboptimal FT3 (2.9 pg/ml) and really high RT3, but normal cortisol levels (13.940 ug/dl at 10 am with RR for 7-9AM: 4.3-22.4 ug/dl), what else would be causing the clinically high RT3?

Jacqueline Gang

Can Reverse T3 be too low? Is this indicative of thyroid imbalance?

Thank you ~Jacki

stefanie Aring
stefanie Aring

I have a patient I am a bit confused about how to interpret her thyroid data. Here are her labs:

TSH is 1.269 units/L
Free T4 is 0.9 ng/dL
Free T3 is 3.2 pg/mL
Reverse T3 is 6.2 ng/dL (range is 9-27 ng/dl)

I think if I did the math right, that makes her Free T3 to Reverse T3 ratio 0.05 pg/mL. Is that correct? And if that is correct, we would say that is optimal, even though the lab reports her Reverse T3 levels are low? I am thinking her free T4 is low, so she is low in reverse T3 because her body is converting her T4 into free T3 instead of reverse T3. Is that also the correct way of thinking about this? I think I believe I know why her Free T4 is low, I am just trying to wrap my head around interpreting the data and making sure I am getting the information down correctly. Thanks for your help!

SAFM Team
Reply to  stefanie Aring

Yes, the reverse T3 is notably low and the fT3 seems quite ample. We assume you are asking this question because your patient has hypothyroid symptoms, and if so it’s necessary to also consider the role of cortisol and estrogen that will affect the cellular levels/activity of thyroid hormones.

John Castella

Hi SAFM Team,

Apologies but I am stuck on the “math”….. ” If FT3 is measured in pg/dl (e.g. 320), and RT3 is measured in mg/dl (e.g. 15), then the target ratio is indeed 20 or higher.”….

Looking at a FT3 value of 315 pg/dl, and a RT3 value of 20.40 ng/dl, the calculation seems to make sense. But if I convert 20.40 ng/dl to mg/dl = .0000204, the calculation is weird.

Did I do something wrong here? So sorry if I have missed something and appreciate your patience.

Thanks, John

SAFM Team
Reply to  John Castella

No problem, John, and glad to know you figured it out. For all others who may also get ‘stuck on the math’, there is an additional explanation posted at the very bottom of the post, right underneath Tracy’s signature. Please note the three asterisks ***

Achina Stein
Achina Stein

Excellent article Tracy!

SAFM Team

If there is no Free T3 on the labwork, but I have a total T3 and a reverse T3, can you tell me the ratio that can indicate the impact of stress/cortisol on hypothyroidism?

Deborah Beaumont

Really great summary Tracy. I found myself explaining this to a client this morning. Your explanation is more smooth though 🙂