Thyroid Thursday Episode 57: What Happens When You Take T4 Hormones?
What Happens When You Take T4 Hormones?
Hey, everybody. It’s Dr. Eric Balcavage, and we’re back for another edition of Thyroid Thursday. And today, I want to talk about what happens when you take T4. Whether your gland makes T4 or when you get prescription T4, what happens to it? In conventional medicine, we’re kind of taught that T4 gets into the bloodstream, it gets transported into the cells, it gets converted into T3, and it binds to receptors in the nucleus, and that stimulates the metabolism. And that there this linear action and that it is that simple,and that all tissues act and behave the same. That’s just not the case. T4 has a bunch of different ways that it can go. 
Once T4 gets into the bloodstream, T4 can be converted into T3 inside the cells. T3 is the active form of hormone, or the most active form of hormone. There’s actually other forms of thyroid hormone that are active, as well. T3 is what we really want to have happen. T4 or T3 get into the cells, T3 binds to the receptors inside the nucleus of the cells. That stimulates metabolism. But under certain situations, like stress situations, T4 can be converted into Reverse T3. Now, very few people have Reverse T3 tested because the assumption is that as long as TSH comes within normal range, that T4 must be getting into all the cells, converted into T3, bind to receptors in the nucleus, and thyroid physiology must be okay. But that’s just not the case, because the brain and the peripheral cells actually behave a little bit differently.
When T4 converts into rT3, this actually decreases cell metabolism, okay? So if you’re making T4 into more Reverse T3, we’re actually likely going to have decreased cellular metabolism. T3 will actually increase cellular metabolism. T4 can also be converted into something called Tetrac. This occurs through a process called oxidative deamination. Not that you need to worry about that, but tetrac can be another product. So T4 may not be converted into T3. It could be converted into Reverse T3, which decreases metabolism, and it could be converted into Tetrac, which could also down-regulate cellular metabolism. And I’ll talk about how that works on another video.
The last thing that can happen to it is T4 can be driven to the liver, and it can be glucuronidated or sulfated, and these are little extra pieces that are bound onto the T4, and that aids in it’s removal and clearance from the body. So just because you get T4, it does not mean that all the T4 you get is going to get converted into T3 and stimulate your metabolism. The assumption may be that that’s what’s gonna happen, but in many cases, this happens(rT3), this happens(Tetrac), or this happens(Glucuronidation or Sulfation). You can have normal TSH levels for multiple reasons, but not get T4 into the peripheral cells of your body, and result in hypothyroid symptoms.
Now, why does it happen? I’ve talked about this many times. The cells in the brain, especially the pituitary and the hypothalamus, act a little bit differently than a lot of the peripheral cells in the body. There’s different transport mechanisms that occur(especially in the pituitary gland), there’s different deiodinase enzymes, especially in the pituitary gland, and there are different receptors throughout the body. So all the tissues act and can behave a little bit differently. There isn’t this uniform functioning of thyroid hormone in all the cells because of these mechanisms.
When there’s stress on the body, and we’ve talked about that before, the Cell Danger Response can kick in. That can decrease thyroid transport, it can change the thyroid enzyme activity, and we can have more Reverse T3 formed, more tetrac, or we can have more T4 sent off to the liver to be cleared from the body. Okay? Hopefully, that gives you a little bit more insight. Look forward to more Thyroid Thursday videos in the future, and if you have any questions, put it below wherever you watch this video. Take care.
