Thyroid Hormone Levels: T3 and T4 Part II

Published on Author John

Thyroid Hormone Levels are important to understand when you’re dealing with thyroid dysfunction. Two of your thyroid hormones, T3 and T4 hormones, are a huge part of ensuring your thyroid is functioning optimally. The difference between T3 and T4 thyroid hormone levels is a big deal and if your thyroid is not functioning correctly, you must understand the role each of these hormones play in order to heal your thyroid, which controls nearly everything in your body!

Thyroid hormone levels of T3 and T4 are so important to understand if you want to have a healthy thyroid, metabolism, weight and overall health!

The below information on thyroid hormone levels is a combination of what I learned throughout the last decade of healing my hypothyroidism as well as information from the following Functional/Integrative doctors: Amy Meyer’s M.D., Mark Hyman M.D. and Aviva Rohm M.D., all of whom I truly admire and agree with on many levels. Click on each of their names for additional thyroid information.

Before you start reading this feature, please start by reading Part I so that this all makes sense to you. There is a wealth of information there.

The Difference between T3 and T4 Thyroid Hormone Levels

We left off chatting about the storage of T4 in your tissues but how does our body take it out of there and convert it into the active T3 hormone? This is so important to understand for anyone going through thyroid issues or anyone who is stressed out, not sleeping enough, exhausted, fatigued or feeling run down, because those can be sure signs of a sluggish thyroid- even if your blood work doesn’t show it yet. We’ll be talking about how the food you eat impacts your thyroid–something that is KEY for healthy thyroid levels, metabolism and energy level- since your thyroid controls both of those!

It’s key to understand that when your thyroid isn’t functioning properly, it messes up your cellular function in your body, which we’ll talk about below (this cellular function controls your weight, energy, brain function, heart rate and more). This “mess up” is what causes a huge bag of symptoms that often do not seem to be related, which is why thyroid issues are often mis-diagnosed or undiagnosed.

That’s what we’re going to chat about today and I cannot stress enough how important it is to understand thyroid hormone levels and the difference between T3 and T4. You have to break it down for yourself with baby steps so you truly understand what’s going on inside your body. If you don’t, you’re just listening to some random person who tells you to take a tiny white pill and you have no idea why. You must do the work to understand what your body is trying to tell you by shutting down your thyroid if you want to heal.

Okay, so let me make this as easy as I can for you. Whichever part of the body needs more thyroid hormone, the conversion from T4 into the active form T3 is triggered by that area. But, the conversion is actually made in the liver, brain, thyroid, muscle and the gut! What’s interesting here is that if your gut needs more help digesting certain foods, your gut cells actually need more thyroid hormone. If you’re stressed out with travel plans or from your kids, your brain needs more thyroid hormone. If your arms are tired from playing basketball, your arms need more thyroid hormone. As I mentioned in Part I, all of your cells, yes every single one of your cells needs thyroid hormone!

Something I learned from my Functional MD’s from the very first session was that for the actual thyroid conversion, you must have adequate levels of zinc, selenium and iron for optimal function. This is why it’s SO important to make sure you are eating foods that are rich in zinc, selenium and iron and supplementing with a good quality supplement if needed. The type of food you eat is key because your body needs these nutrients for proper conversion. So, one of the outside iodine atoms that we chatted about in Part I is let go from T4 and it turns into free T3- now this is the big guy who’s going to energize your cells. What we are looking for is to get T3 into our cells because T4 isn’t active and therefore doesn’t help us if it doesn’t convert.

Now, the T3 has to get through the membrane of each cell and it needs cortisol to help it do that. Cortisol also reduces your ability to release estrogen from your body through your liver. And high estrogen makes a high TBG thyroid-binding globulin, which binds onto thyroid hormones. This form isn’t active so your thyroid levels sink even further even when your thyroid is doing everything it’s supposed to be doing and your lab tests may appear to be normal! Yes, you heard me correctly: Cortisol. Why? Because Cortisol is key in the relationship between your stress, your adrenals and your thyroid, which we’ll chat about in the next part of this post. So, if you have low cortisol (Like I did for over 10 years), your T3 is going to have a tough time moving from your tissues into your cells. Without enough cortisol in your body, you can’t get enough T3 into your cells and you’ll end up with Hypothyroidism and it’s awful symptoms such as weight gain, fatigue, hair loss, dry skin, etc. This is EXACTLY what happened to me. I had super low cortisol and my thyroid was super sluggish in my 20’s. So, the name of the game is to not have too high or too low cortisol because that will effect your thyroid. Always make sure your doctor is checking your cortisol levels through a saliva test (not blood test) to get an accurate reading and assess your situation.

Your cell membranes (cell walls) also need to be healthy because they let your cells take IN the hormones and nutrients they’re in need of while it keeps OUT the toxins and other bad guys that can disrupt the process.

So, what do you need for healthy cell walls?





Eating unhealthy, inflammatory fats such as trans fats or hydrogenated fats destroy the health of the cell walls and mess up your gut health- a huge disaster. Say good-bye to those processed foods full of inflammatory fats and all those fake butters and fake fat-free ingredients that are in products such as I Can’t Believe It’s Not Butter. Yes, I once at this junk and I still can’t believe it.

So, if your body converted your T4 into T3 from the help of cortisol, you still need to look deeper at your mitochondria to make sure these guys are optimally functioning. Your thyroid is in charge of your metabolism and you’ve got tiny mitochondria inside each of your cells. The mitochondria take glucose and oxygen and convert them into energy and T3 helps make this run smoothly. Your thyroid sends out thyroid hormone into each cell, which keeps your mitochondria and YOU happy.

Understanding the difference between T3 and T4 and your thyroid hormone levels is a huge piece of your journey that must be understood by you because many doctors do not know the difference or what is causing either one to be high or low. You must take your health into your own hands and figure this out and work with your doctor. It’s a team effort. That’s the only way I healed. I did the work and you must do it to. Believe in yourself. You can do it. I know you can.


Next we’ll be talking about Reverse T3 and how to further support your thyroid hormone levels in Part III.

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