T4 to T3 Conversion: Factors That Decrease Thyroid Function (& How to Prevent it)
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T4 to T3 Conversion: Factors That Decrease Thyroid Function

This is lesson #5 in the thyroid beginner series. 

As you know, this series is designed to help you understand the most basic concepts about thyroid function so you can be a better advocate for your own health

Today is all about T4 to T3 conversion. 

This is the process by which your body creates and activates thyroid hormone. 

It's important because there are steps that you can take to actively enhance this conversion process and help reduce (or improve) your symptoms. 

Let's jump in: 

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T4 to T3 Conversion Explained in Plain English

This is really a continuation on the concepts that were built upon in lesson #3 and lesson #4 which discuss T4 and T3 thyroid hormones. 

They are short videos (less than 10 minutes each) so if you don't feel like you have an understanding of thyroid hormones then go watch those before you jump into this lesson. 

As I stated previously, T4 to T3 conversion is the process by which your body takes inactive thyroid hormone and activates it. (1)

This process is also known as thyroid conversion or peripheral thyroid conversion but don't let this confuse you because they are all referring to the same process. 

In this conversion process, your body takes T4 thyroid hormone, that it either produces on its own or that you've taken by mouth, and cleaves off a portion of the molecule which changes its shape and structure. 

This change alters the hormone to T3 (triiodothyronine) which is the active thyroid hormone. 

Why is this important?

Because the more T3 you have in your body the better your thyroid functions

The less T3 you have in your body the more symptoms you will experience

What that means for you is that you want this process to be working at 100% because if it isn't then you will be producing less active thyroid hormone. 

Thyroid adrenal reset complex 400 x 350

It turns out that the way that your body increases or decreases this conversion process is through the activity of special enzymes. 

These enzymes, known as deiodinase, are responsible for "cleaving" off an iodine on the T4 hormone. 

T4 is named T4 because it contains 4 iodine portions on the hormone. 

Once it loses an iodine portion it now only has 3 and we call it T3. 

Approximately 80% of the T3 in your body is created through this conversion process which means it's very important for thyroid health. 

This conversion process matters if you have a thyroid, if you don't have a thyroid, if you have Hashimoto's, if you have thyroid nodules, if you have thyroid cancer and so on. 

Why?

Because even if your thyroid isn't working you still have to take thyroid hormone by mouth and most thyroid medications contain T4 (not T3). 

Factors that DECREASE T4 to T3 Conversion (These slow down thyroid function)

There are certain factors which can slow down the conversion of T4 to T3 by interfering with the efficiency of the enzymes responsible for this conversion.

These factors act like a brake on your entire thyroid system. 

They slow down the amount of T3 that your body is able to produce and may make less efficient the medication that you are taking.  

If you can address and reverse these issues then you can "release" the brake on your thyroid and finally start feeling better! 

I've created a list of the most common factors which blunt this conversion process below: 

  • Dieting & Calorie restriction (slows down your metabolism) - Calorie restriction, as little as 1,500 calories per day for 3 weeks, is enough to blunt thyroid function and reduce T4 to T3 conversion. (2) This might be the #1 problem for many thyroid patients who also tend to struggle with weight. They get trapped in a situation where they are overweight but try to diet to reduce the weight, only to further reduce thyroid function which leads to weight gain. 
  • Inflammation (from any cause) (3) - Inflammation is really nonspecific but inflammation from any cause (if systemic) can damage thyroid function. You can identify inflammation by looking for markers such as CRP and ESR. If elevated, these may be an early sign of inflammation. 
  • Lack of sleep (4) - If you are sleeping less than 8 hours per night then you may be reducing your thyroid function without realizing it. 
  • Intestinal issues (Dysbiosis, IBS/IBD, etc.) - A large portion of thyroid conversion actually happens in the GI tract or gut. (5) If you have problems in the gut then this may limit your ability to convert T4 to T3. Problems such as intestinal dysbiosis (changes in gut bacteria), inflammatory conditions such as SIBO/SIFO/IBD, and other issues can all cause issues. Treating gut related issues should be a priority if you have thyroid disease. 
  • Stress (emotional, physical, etc.) - Stress, from any cause, will limit thyroid function and block thyroid conversion. (6)
  • Chronic and acute infections - Acute infections such as pneumonia can cause issues but also more chronic infections such as viral or bacterial overgrowth syndromes can also cause issues. 
  • Medications - It is well known that certain prescription medications can block thyroid function. (7) Included on this list are blood pressure medications, diabetic medications, seizure medications, iodine, PTU/Methimazole, steroids, and heart medications like amiodarone. It may not be possible for you to stop taking your medication but you should look for alternatives if possible. 
  • Endocrine disrupting chemicals (those you come into contact with daily, some people more sensitive than others) - Endocrine disrupting chemicals are chemical compounds that humans come into contact with on a daily basis which look like real hormones but aren't. These hormones can trick your body into thinking the real hormones are there and they may compete for binding on cellular receptors. (8) EDC's are found in plastic bottles, on receipts, in foods and so on. Limiting your exposure to these chemicals may help improve your thyroid function. 
inflammation reduces t4 to T3 conversion

If you have any of these issues going on in your body then your thyroid function may suffer. 

These conditions may lead to an increase in a metabolite known as reverse T3 (a topic for tomorrow). 

Reverse T3 is the metabolite created when your body is having trouble with the thyroid conversion process. 

Therefore, it can be used as a marker of thyroid conversion in your body. 

You can test for reverse T3 with a simple blood test. 

Factors that INCREASE T4 to T3 Conversion (You can use these to improve how well your thyroid works)

So what are you supposed to do if you have any of the factors listed above?

This section will discuss some of the available therapies that you can use to potentially help improve T4 to T3 conversion. 

  • Fixing the problems listed above (you must know what is causing the issue!) - The first, and most important, option is to try and find the root cause of your issue and address that problem. This may require a physician to help but in many cases, it will not. For instance: if you know you are struggling with calorie restriction then the first step is to stop that behavior! If you have known gastrointestinal issues then you can address that problem with basic therapies such as probiotics or enzymes. If you are struggling with stress then adding yoga or meditation to your daily regimen can help. If you are having issues with sleep then you can focus on ways to improve that and so on. Some issues, such as the use of medications, may require that you find a physician to help (and even then you may not be able to adjust your medications). In many situations, you may find that you have a number of factors which are limiting your T4 to T3 conversion. Each of these factors may contribute 5-10% so you may have to address many issues to see noticeable improvement. 
  • The use of certain supplements - Another strategy to improve T4 to T3 conversion is to use certain supplements. Supplements such as zinc, selenium (9) and guggul may all help your body naturally improve this process. The use of minerals such as zinc and selenium will only help if you are deficient, but many people around the world most likely are due to poor widespread dietary patterns. I've included the most effective mix of nutrients and vitamins in my T3 conversion booster which has helped many people improve thyroid function. You can learn more about that supplement here

Using these strategies can help you increase thyroid function naturally and may even help if you are taking medication. 

Remember:

If you are taking thyroid medication your body still must convert T4 into T3. 

So all of these factors still matter if you are taking thyroid medication or if you don't have a thyroid at all. 

The good news is that almost everyone with thyroid related issues can benefit from this information. 

Bypassing T4 to T3 Conversion with T3 Medication

Another strategy that we will discuss (briefly) is the use of T3 thyroid hormone to bypass T4 to T3 conversion. 

We already discussed the importance of T3 and how it does pretty much all of the heavy-lifting when it comes to thyroid function in your body. 

Normally, thyroid medications which contain T4 must be activated to T3 before your body can really use them

But you can skip out on this process by using T3 medications such as liothyronine or Cytomel. 

If you ingest T3 medications then they do NOT require activation in the way that T4 medications do. 

This allows you to bypass the conversion process and to start feeling better almost immediately. 

This doesn't mean that you should skip out on all of the therapies listed above, but instead combine them all together for maximum benefit. 

I find that using medications which contain T4 + T3, using supplements designed to improve thyroid conversion and addressing issues which blunt thyroid function all at the same time cause the best results clinically. 

You can learn more about using T3 medications here

Conclusion

The bottom line?

Addressing this tiny concept known as thyroid conversion may be one of the most important things that you learn about your thyroid. 

Most of the time, patients feel helpless with their thyroid because so much depends on their doctor and what he/she is willing to do. 

But if you understand your thyroid you can take steps to optimize whatever thyroid function your body is capable of producing

Just remember:

This is a process and it takes time!

Don't expect immediate results, but instead give your body weeks to months to improve. 

Now I want to hear from you:

Are you struggling with T4 to T3 conversion? 

Have you tried therapies designed to improve this process?

Have they worked for you? Why or why not?

Have you tried T3 medications?

Leave your comments and questions below! 

Westin Childs
 

Dr. Westin Childs is a Doctor of Osteopathic Medicine. He provides well-researched actionable information about hormone-related disorders and formulates supplements to treat these disorders. He is trained in Internal Medicine, Functional Medicine and Integrative Medicine. His focus is on managing thyroid disorders, weight loss resistance, and other sex hormone imbalances. You can read more about his own personal journey here.

Click Here to Leave a Comment Below 14 comments
Genia - July 2, 2018

Yes! I’m hoping my endocrinologist will add T3 to my treatment. I wish there were doctors like you in Georgia. I am struggling with just T4. I just want to feel normal.

Reply
    Westin Childs - July 3, 2018

    Hi Genia,

    T3 helps a lot of people. Keep us updated on your progress!

    Reply
Sameena Hussain - July 3, 2018

Recent blood test show I am not converting t4 to t3. But gp says I am ok.i am on 100mcg levothyroxine and but feel awful. 15kg weight gain , hair loss etc. Went to private who recommended 50mcg of t3 , 50mcg of t4, ldn and Dr Wilson adrenal blocker ? Have yet to receive the meds. Will this help ? Blood Results THYROID STIMULATING HORMONE* 4.45mIU/L

FREE THYROXINE 18.8pmol/l

FREE T3 3.2pmol/l

IMMUNOLOGY THYROID ANTIBODIES.Thyroglobulin Antibody 66.5IU/mL

Method used for Anti-Tg: Roche ModularThyroid Peroxidase Antibodies* 526.0 REVERSE T3* 25ng/dL

Reply
    Westin Childs - July 3, 2018

    Hi Sameena,

    It may help, but there’s no way of knowing until you try it.

    Reply
Kirsten - July 4, 2018

I’m on 100mcg levothyroxine and 25mcg Levothyronine (2x 12.5mcg/day). All my thyroid hormones seem to be in the happy middle but I have gained 30lbs on top of all the weight I had gained before…. I wonder if I should stop taking levothyroxine and only continue with levothyronine. May ask my doctor to increase dosage of levothyronine to 2x25mcg/day

Reply
    Westin Childs - July 4, 2018

    Hi Kristen,

    You may also want to look at other hormones such as insulin and leptin as well.

    Reply
      Kirsten - July 4, 2018

      I have checked both insulin and lepton and both are in normal range.

      Reply
Dennis Keith Welch - July 4, 2018

I have tried Naturethroid (had major digestion issues), Armour and NP (both Armour and NP made me feel grouchy). I was on NP and started breaking out on my face. I had to go back to levothyroxine and doctor wouldn’t prescribe T3 meds. Currently, my Free T3 (3.1) and Free T4 (1.6) has improved but my TSH is crazy low, .05. Also, my Reverse T3 has gone back up and is now 17. Would the T-3 conversion supplement help. And, should I be concern about my low TSH number.

Reply
    Westin Childs - July 5, 2018

    Hi Dennis,

    The supplement may help, but there’s no way to say for sure.

    In regards to your low TSH you can read more about that here: https://www.restartmed.com/suppressed-tsh/

    Reply
Kim Diedrich - July 14, 2018

Hello Dr. Childs, I have 45-50 lbs weight gain, thyroid & adrenal symptoms. I think I need more T3 but am afraid to take it without your guidance. I’ve read to take bile, what do you think of that?
2001 I was 44 yrs, on TriPhasal, had a lot of stress work/ personal life. I fasted losing 40 lbs, went from 155 lbs to 115 lbs. The weight increased without proper nutrition. HFCS in foods and sugar and dairy, ate salads w/HFCS dressing. Mushrooms and tomato nightshades were stopped. In 2007 about 120 lbs, had an ear infection from impacted wax and it went to the other ear. I took many antibiotics Levequin, Avelox, Bactrim. I lived by a woods which had bacteria and fungus. I was in perimenopause and my sex hormones were imbalanced, I think this was causing my hearing loss. I went on William Crook’s candida diet and moved from the wooded area. I took New Chapter All Flora probiotic which they don’t make anymore, it helped. I continued trying to get better and alleviate my chronic fatigue and weight gain. I thought it was allergies.
2013 I went to a conventional NP who prescribed BHRT, first 80/20 bi-est which caused breakthrough bleed. She then prescribed .375 estidiol/100mg Progesterone & 5 mg Testosterone. She did not test first, prescribed by how one feels . Some things were good, but I began getting chin hair and aggressive so I tested.
A NP tested me in 2015- She gave me ZRT test kit for saliva cortisol and blood spot hormone and nutrient deficiency tests; I was low in AM, morning, more normal in afternoon and high at night for cortisol curve. I don’t feel awake in early morning or afternoon and any stress makes me worse. She also ordered blood spot tests for sex hormones and these:
Ferritin 162 (13-300), B12-1034 (243-894), Folate 20 ( 9.3-30.9), RT3 18.5 (18-25), FT3-3.0 (1.8-4.6), FT4- 1.33 (0.9-1.7), TSH 1.650 (0.27-4.2), TPO AB- 8.1 (<35), TG AB- 124 (<115), Vit D 35 (30-100).
She diagnosed me w/Hashimotos by Thyroflex & prescribed BHRT 0.2 estriol/0.2 estridiol, 100 mg Progesterone and 5 mg Testosterone.
She prescribed 5 mg DHEA & adrenal supplements. I began to feel better on the adrenal supplements and BHRT but was afraid to take the 60 mgs NP Thyroid and DHEA. I started those after. I started speeding, heart palps, eye changes, and I started and went off of the NP Thyroid in 2 days and experienced intense undulating pain on my scalp. I continued 5 mg DHEA and had severe loss of facial collagen in cheeks, next to nose, which looked like the women who take steroids. Dark circles and wells under my eyes not previously there. I tried botox in 2015 for the eleven creases between the eyes, had swelling reaction and fat pads under my eyes reduced and moved.
My TSH fluctuated from 0.57 (.40-4.70) on 11/23/2009; 4.27 (.40-4.70 UIU/ML) on 4/11/2013; 2.42 (.40-4.70 UIU/ML) on 01/23/2018. I have high cholesterol. How do I know if I should go on T3 without causing more speeding and collagen loss? Do you think it was going off of the NP Thyroid or the DHEA? DHEA-S –132mcg/dL (<15-200) 2013 DHEA-S 1.5 ng/ML (2-23) in 11/24/2015

I'm off BHRT now due to hyperplasia and had pain during and after vaginal ultrasound, am afraid to have another one. I was applying the BHRT cream between thighs. I have stomach & thigh fat, butt is flattening out, eyes are dry from meibum thickening/clogged glands; pre diabetes; high cholesterol; hair thinning; nail ridges (only after starting and stopping NP Thyroid in 2 days), fatigue; limited energy, vertigo from ear infection.

Reply
    Westin Childs - July 16, 2018

    Hi Kim,

    It seems that you have a lot going on based on this history here. Because of the complexity, there’s really no way for me to give you advice but what I do think you should do is seek out a physician who is knowledgeable and who can help you further. You can use this as a resource to help get you started: https://www.restartmed.com/thyroid-doctor/

    Reply
Jenny - August 28, 2018

I had my thyroid ablated in 2005 (from Grave’s disease).

Recently, with the help of my Naturopath, I reduced my usual levothyroxine-only therapy from 150mcg to 137mcg to 112mcg and now 100mcg (and switched to Synthroid), while newly adding (and titrating) T3 to a level of 15mcg. (Long-short: I’m currently on 100mcg Synthroid and 15 mcg liothyronine daily.)

Q1: Is this a proper ratio?

Q2: Does taking a T3 med cause more of the T4 med to be converted to RT3, since T3 needs are now being met by T3-only medications? Do RT3 levels go up when patients add T3 to their T4 regimen?

Q3: Is it worthwhile to take 5mcg T3 three time a day (spaced at 4 hours apart)? I’m looking to get rid of the 2pm energy crash, but don’t want the fast/strong heart rate that taking two 5mcg together seems to give me.

Ps. I’ve only been on T3 for two weeks. We increased 2.5mcg every 3 days until I reached 15mcg. Hoping that wasn’t too fast, after just reading your article that said to increase every couple of weeks.

Reply
Corinne Sharpe - August 31, 2018

Hello! I had a total thyroidectomy due to cancer. Would the conversion supplement assist even though im 100% dependant on medication?

Reply
    Westin Childs - August 31, 2018

    Hi Corinne,

    The short answer is yes because your body must still convert the T4 that you take (through levothyroxine or Synthroid) into the active T3 in peripheral tissues.

    Reply

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