In this educational video Dr. Paul Anderson explains why the thyroid produces several distinct hormones and how they affect health. He begins by outlining the three primary cellular targets of thyroid hormone action: an external T3 receptor that opens glucose transporters, and intracellular pathways that stimulate mitochondria for energy production and the nucleus for protein synthesis. He then describes thyroid hormone synthesis, starting with the amino acid tyrosine and sequential addition of iodine to create T1, T2, T3, and T4, noting that T4 (levothyroxine) is the predominant circulating hormone while T3 (liothyronine) is the active form that directly binds cellular receptors. The conversion of T4 to T3 via deiodinase enzymes in the liver and peripheral tissues is explained, emphasizing that only T3 can activate cellular processes. Dr. Anderson introduces reverse T3 as a fifth, stress‑induced hormone that binds the same receptors but shuts them down, acting as a protective mechanism that can become pathological in chronic illness, long‑COVID, or after intensive drug therapies. He discusses how elevated reverse T3 can cause fatigue and multi‑system slowing despite normal TSH, T4, or T3 labs, and why testing reverse T3 can be valuable in such contexts. Treatment strategies are covered: addressing underlying stressors, detoxification, and, in severe cases, low‑dose therapeutic T3 to outcompete reverse T3 at receptors, always paired with holistic health improvement. Finally, he warns that simply increasing T4 (e.g., raising Synthroid dosage) without adequate conversion capacity can raise reverse T3 and worsen symptoms, underscoring the need for individualized endocrine management, especially in pregnancy. The video concludes with a call to explore related content.
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Hey, it's Dr. A. This was a great question that came in. Thyroid hormones, why are there so many? Because it seems like it's really hard to get them balanced up when they get out of balance. So, wonderful question. This is my YouTube channel. Welcome. I'm Dr. Paul Anderson, and I get into natural and integrative healthcare questions. I answer questions that come in through social media, et cetera. And do I answer all of the questions that come in? No, because there would be not enough hours in the day, but I do as best I can. But I wanted So let's dive into today's topic, which is why are there different thyroid hormones? What's the purpose of them? And how does that relate to my thyroid health and the way my doctor might want to treat me? So the first thing is, what's the thyroid hormone do? Well, to think of a thyroid hormone going out and doing something, there are 3 primary targets when it gets to our cells where thyroid hormone works. And so we're not talking right now about which kinds of thyroid hormone. I'm just telling you the big picture. The first target is actually on the side of your cell. There's an external cell receptor, and that is for the T3, T number 3, the active thyroid hormone. And what it does is it turns on, sort of opens doors to feed the cell. Now, why do we want to do that? That's because when the thyroid hormones are out and they're running around and they're doing their cell thing, what they do inside your cell is they feed 2 separate processes that require different types of substrate, different types of food. To go in. One is your mitochondria to make energy. That's your metabolic rate. And so that the thyroid on the outside of the cell opens up a glucose transporter to let some glucose in. And then the other is the nuclear membrane. So your nucleus, and that does whatever the nucleus of your cell does. It could be there for cell replication. It could be there to make some organelles, to do whatever it's doing. On that side, what you really need in there is amino acids. And so on that side, it opens a door that lets amino acids in. And so people will often forget that There's a feeding system that has to operate in order for the thyroid inside the cell to do these two very major functions. When we make thyroid, a common question is how do we make it? Comes from our thyroid gland, which sits here in the lower part of our throat. Looks sort of like a little you know butterfly-shaped gland, and the thyroid gland is very complex, which is fine. But basically, the manufacture of thyroid is actually not that complex. The hormone that comes from your pituitary. Pituitary gland, which is actually stimulated by an area above it. But the pituitary gland releases this thing called thyroid stimulating hormone, TSH, which you probably had tested if you ever had your thyroid tested. And then that goes down and then that turns on areas in the thyroid gland proper where the synthetic machinery to make thyroid hormone goes on. And there's actually 4 types of thyroid, but we usually just talk about 2 of them. Now, I said there's 4 types, There's four types that are made normally. There's a fifth type, which we're going to have a special little talk about, which is sort of unique on its own. But what we do is we take the amino acid tyrosine, and then we start adding iodine molecules onto it. So a T1 molecule, the first one, is a tyrosine with one iodine. A T2 hormone is going to be a tyrosine with two iodines. Normally, we don't talk about those that much because they're still inside your thyroid, and they don't really—they don't fit into a lot. therapeutic protocols. People experimented with that about 20 years ago. But then you get to T3 and T4, and again, it's a tyrosine with either 3 or 4 iodines stuck onto it, right? So those are your primary circulating hormones. What's the one that's most produced? T4 is also called levothyroxine. And then T3 is made in a smaller quantity, and that is called lyothyronine. 2 is basically T3. What happens is somewhere around 70 to 85% of what comes out of your thyroid is T4. T4 is not very active because it has to have one of these iodines taken off. There's about 20, 25, 30% of what comes out of your thyroid is T3. It's active and ready to go. Your body has a way of sometimes making hormones in an inactive state so that they go to where they're supposed to go. And then they get activated when they get home, which is your cell. So when you're thinking about this, we're going to dump out the majority of a T4, a bit of T3, and that's going to go out. And then remember I said we have a receptor on the outside of the cell and that opens the doors to feed the cell. And then inside the cell we have the mitochondria and the nucleus getting turned on by the thyroid. Who's inside the cell turning things on, T4 or T3? Well, it's going to be T3. Not T4. Here's the other thing: who opens the doors on the outside? The doors on the outside are opened by T3. All this T4 that's floating around can't do anything until it's converted to T3. There's two major places that you do this conversion of T4 to T3, and one is your liver can help you out with that. There's a deiodinase, right? So if I have four iodines and I need to make it three iodines, then I need a deiodinase. I need to take away an iodine. Right? I've also got deiodinases inside myself, thankfully, because then T4 can go in and be turned into T3. You have to have some amount of T3. But what happens if your body gets under stress? Because remember, what's the whole punchline of this? We're opening up these doors to feed the cell, making the nucleus work harder. We're making the mitochondria work harder. Punchline is we make the cells go faster and work harder. What if your body gets stressed or under certain drug influences or other things, or you've been sick a long time and your body decides, hey, this is too much cell activity, we need to Slow this person down so that they can recover. This is the global body thinking, right? There's not like conscious thought behind this probably, but this is a biochemical and physiologic process. So the 5th type of hormone, which is the one I said I'd talk about separately, is called reverse T3. And it's the same as the T3 that turns on everything, only it's a mirror image. And so when it goes and binds to the outside door receptors or goes and binds to the inside receptors at your mitochondria or your DNA, Guess what it does? It shuts them off. So reverse T3, I used to tell patients it's evil T3. It goes and turns everything off. Well, now this is a safety mechanism your body has developed, so there's not really something wrong with it, but we don't find a lot of help in testing reverse T3 in healthy people because there's going to be some around. It's not going to matter, right? But in chronically ill people and in this world of long COVID patients and People who have had a lot of, you know, heavy drug therapies that they've had to go through for, you know, cancer or hepatitis or something. Testing reverse T3 can be very helpful because it can say how stressed is the body and how much does the body try to protect your cells. The problem is, like all protection things that your body does, it can go too far. So if I make too much of this reverse T3, then I can slow my cells down so far that I develop chronic fatigue. My other cells don't work right. My brain slows down. My reproductive system slows down, my digestive system slows, everything slows down. But then you go to your doctor and they test your TSH, which is from the brain, right? Or your T4, and it looks normal. Or your T3 could even look normal, but it's because you're chronically ill. They didn't test the reverse T3. So it's, it's one other stone to look under, this reverse T3 business. Now, how do we get the reverse T3 to just stop doing its thing? First thing is convince the body that it's trying to heal. So that means dealing with whatever the underlying problems are and getting in there and working on if you've had chronic infections, Or you've been— had surgery and you're recovering, or you get chemotherapy or radiation, or you had some other thing, and feed the body the way it needs to, move the body the way it needs to, detox the body. The next thing though, in real extreme cases, what we'll have to do is we'll have to give people small doses of therapeutic T3. So, the normal thyroid prescription is T4, because remember, that's what mostly is made by your thyroid gland. And that's fine if you're a healthy person and your only problem is low thyroid. Your body's got all the enzymes it needs to turn T4 into T3 and it'll all be good, right? When you get sick and when your reverse T3 levels rise, or if your conversion goes down and you've got all T4 and no T3, you have to have some T3 going in. So, in these cases where the reverse T3 is high or the body under stress is just producing a ton of T4 and no T3, we would just give people a bit of T3, tiny doses. And that is a whole other conversation, dosing of that, because it's done under very hypercritical monitoring and all of that. But, what it does is Then the regular T3 through the dose can go in and it can push the reverse T3 off the receptors, eventually turn things back on. And then because you're going to be working on the other reasons that you got sick, then the body can go back to operating more normally and it'll stop making reverse T3. The thing that you have to keep in mind is it's not just a one-trick pony thing. It's not just dumping T3 in there and expecting that to do all the work. Your job and your goal is, if you have to use T3, is to do that in concert with fixing the underlying problems and then working to get your body healthier. And as your body gets healthier, your dose of your thyroid hormone normally can go down, and sometimes the T3 dose can totally go away if you get healthy enough. And there's a million reasons why that may or may not happen, but that's the bottom line of how it does it. We talked about, you know, these five different types of hormone. There's the T1, T2, T3, T4 that are the regular. And then the reverse T3 is the 5th one. We talked about kind of how they work, kind of why they go bad when you get chronically ill. And then a lot of people will ask, well, T3 is the active form, can I just use T3? Because on this channel we don't give specific medical advice, my answer to that is that would be a distinction between you and your endocrine provider, whether that's your primary care doctor, endocrinologist, whoever does your thyroid prescribed. You do need to know that when you are pregnant, generally there are different needs for T4 versus T3. That has to be managed very carefully, and again, that's an individual thing. And then there are some people, uh, you know, who do very small doses of T3, and that, that seems to work fine for them. As I said in the beginning, if you're not a chronically ill person and you haven't had all these stressors, your body probably will work fine on a regular thyroid, which is mostly T4. But if it's not, there's all these other reasons why that might be going on. Now, the one final thing, and this is a question I got, must have been 10 times after we did the last thyroid talk, and that was that my doc raised my T4. So Synthroid is the trade name for it, you know, the levothyroxine, right? And now I'm more tired. What happened? Well, there's a number of things that can happen. One of them though is if there's other underlying problems going on in your body, And your doc says, well, you do need more thyroid, and they kick up the T4 going in. If you don't have the ability of the enzyme to convert T4 to T3, or that 5'-deiodinase enzyme, and/or ton of T4 in you already, body's trying to protect itself because it says, we probably don't need more of this. It'll make reverse T3. And we do see this in patients as well. A colleague refers them over, they're looking, the TSH looks good, but they bumped up the T4, and You know, the T4 level's not that bad. It's a little high, but it's not that bad. T3 level's kind of medium to low, but the reverse T3 is super high. And that's another reason why you could actually trigger a reverse T3 response. And it's not, you know, that just happens sometimes, especially if there's other underlying problems going on. You just back off on one and you increase the other, and that will right the ship normally for you there. Well, I hope this has been good to answer those really great questions you guys asked. If you like this video, Please check out our other videos. Like, share, subscribe, do all the stuff. We do a lot on social media, but all the video content we're keeping on YouTube so you get one place to find it. And we got a ton of playlists, and this will be in a particular playlist as well. But check out these other videos. I'm Dr. A. I'll see you on the next video.
