A few years ago, I wrote a blog post explaining why T3 (Liothyronine) is best taken in multiple doses during the day. This blog post is a follow up to that one, based on a series of questions and answers that happened recently between a thyroid patient and myself. You may find it interesting.
Q1: Just something I’m curious to know. I’ve read that the half-life of T3 is between 6-8 hours. How does it maintain an optimal body temperature over 24 hours if that half-life is correct? Thank you.
A1:
The blood half-life is about 24 hours. However, most people feel that a T3 dose only seems to last 4-8 hours. The blood half-life is largely irrelevant apart from lab testing considerations.
When someone takes a reasonable sized T3 dose, for example 10 – 25 mcg of T3, the FT3 peaks in the blood during the first couple of hours of swallowing it. The T3 begins to enter the cells and connects with the thyroid receptors in the cell nuclei. This begins to increase the rate of gene transcription within the chromosomes of the cell nucleus. As more T3 arrives from the dose, the rate of gene transcription increases. This makes the cell function properly and produce the proteins that it is supposed to. Even when the blood FT3 levels eventually begin to fall after 6-10 hours the effect on the cell nuclei continues.
One dose of T3 per day, taken at the size it would need to be to facilitate enough T3 to keep the cells working for 24 hours, is usually far too large for most people to deal with and some people have a much faster clearance of T3 which also makes it difficult to cope with one dose.
However, 2-4 doses over the day usually is enough to ensure that more T3 begins to rise in the blood again before the cell nuclei have lowered the rate of gene transcription – thus allowing the cells to chug along at a nice rate, even though the blood levels might fluctuate.
So, this is all about what happens in the cells and nothing at all about the blood levels. None of the interesting stuff can, of course, be measured directly unless we dissected you – which I think would be somewhat unpalatable! All we can do is measure the effect of the T3 – hence signs and symptoms are our best assessment of how the cell nuclei are getting along. See my books for more about using signs and symptoms and managing T3 dosing (and the dosing of the various thyroid medications).
This is also why multi-dosing of T3 works so well and can work far better than slow release T3 when someone is using a good amount of T3 or T3-Mostly or T3-Only.
But basically, we can do really well over 24 hours once the cell nuclei have got their momentum up with the T3 doses and have the right rate of gene transcription in process. Yes, it can go a little slower during the night while we sleep but that’s fine as we aren’t as active. Some need more T3 in the night to allow the pituitary to function well enough to make cortisol (hence the Circadian T3 Method – see my books for more on CT3M).
I hope that explains it.
Q2: It’s very nice to have this explanation. What I don’t understand is, what is the blood FT3 doing?
A2:
The blood FT3 is doing absolutely nothing. T3 does nothing until it is transported to the cells. Most of its work happens at the cell nuclei and also at the mitochondria. When someone has no T4, the T3 can also operate at the cell wall thyroid receptors. But in the blood – nothing at all. The T3 just circulates so that it can reach the cells of the tissues and organs throughout the body.
This is the problem with doing blood testing. Blood testing is a kind of surrogate measure of what might be happening at the cell nuclei. But we don’t know how effective the transport into the cell nuclei through the cell wall is. We don’t know how easily the T3 can reach the nuclear thyroid receptors.
But doctors think they can measure FT3, FT4 and say we are ok – just based on a poor surrogate measure. Even though our signs and symptoms might suggest we are very hypothyroid still. Some doctors even think that TSH is even a surrogate measure for FT4 and FT3 and rT3 – which is even more silly. Some don’t even measure the active hormone FT3. The entire current paradigm of endocrinology practice is really flawed.
This is why my books focus on the use of signs and symptoms, with blood tests giving only an indication that dosage changes are moving things in the right direction. Even aiming for specific blood test targets of FT3 in the range or rT3 in the range is nuts. We don’t know what this is translating to in terms of cellular effectiveness of T3 for an individual.
Some thyroid patients seem to put so much trust in their blood test results and think searching for some magic numbers for FT4 and FT3 is what they need to do. But these results vary from time to time and they really are only shadows of what the real picture is within the cells and the cell nuclei.
Q3: Thank you for this extended explanation. When someone is on quite a lot of T3 they often have to avoid taking the medication for many hours prior to any FT3 test, just to avoid the FT3 result being over range and scaring the doctor, thus having their T3 dosage reduced. A question I have always had is , why would we need our FT3 to be this high at all?
A3: The blood levels don’t matter, especially when measured too close to a T3 dose. The FT3 doesn’t do anything in the blood. If your signs and symptoms are fine then you’re pretty much in good shape. FT3 fluctuates far too much after a T3 dose is taken and it can get very high for several hours before it eventually falls again. The lab ranges are designed for healthy people and those on T4 medication, so they are not really suitable for those on mostly T3 treatment when FT3 levels fluctuate violently in the blood after T3 doses. See: https://paulrobinsonthyroid.com/can-ft3-be-used-to-manage-liothyronine-t3-thyroid-treatment/
Q4: So, it’s okay if we walk around every day with an FT3 level ABOVE range (if we feel good)? The only reason we disguise that is for the purpose of keeping the doctor happy?
A4:
Yes this is true for some people, especially if they are taking a lot of T3 medication. If their signs and symptoms show no evidence of being hyperthyroid at all, then testing FT3 within hours of taking a T3 dose and finding it high is not a concern. If I tested my FT3 within 12 hours of a T3 dose, it would be around 9-10 and my local reference range is 3.4-6.7. So, I tend to leave 18-24 hours and test trough levels – by which time my FT3 is in range.
But you need to be certain your signs and symptoms are good and not suggesting that you are on too much thyroid medication. These include blood pressure, heart rate and body temperature. Checking blood calcium is also good as too much T3 can raise it. An ECG (EKG) is a good idea too during the period of titrating your T3 dose and maybe occasionally thereafter.
These comments would be heretical on many thyroid groups by the way. Even many of the patient groups have been conned into thinking they have to adhere to thyroid lab tests and ranges that are designed for healthy people or those on T4 based thyroid medication. The people in these patient groups often talk about being in the upper quartile for FT3 or lower half for rT3, but they are still playing the lab test game that the endocrinologists and doctors have told us we need to abide by – even if this keeps many thyroid patients in a permanent symptomatic state of hypothyroidism.
Patient’s Final Comments: This reminds me of a recent case study I read on a neuro-endocrinologist’s page (I never knew that was a thing). He had a woman he was treating with T3 who only felt good on HIGH doses of T3 but her heart rate was too high, otherwise ALL her other symptoms were gone. He kept her on the high dose stating there are receptors that don’t need as much T3 while other receptors do need it in certain instances. She was placed on a beta-blocker for her heart with cardiologist approval and is doing fantastic on her higher dose. I was shocked to see a specialist doing this.
Paul’s Final Comments: Well, I can’t comment on the individual case, but it is possible that this can happen. If so, then good for him! He was not restricted by current dogmatic practices.
My original blog post on multi-dosing of T3 is here for reference: https://paulrobinsonthyroid.com/why-t3-or-liothyronine-is-usually-taken-in-multi-doses-per-day/
I hope you found the above useful.
See my Recovering with T3 book for comprehensive information on using T3. See my The Thyroid Patient’s Manual book for a broader review of thyroid hormones, diagnosis and treatment using all the different thyroid medication.
I also offer 1-1 coaching. If interested then use the ‘Contact’ button on the homepage of this website.
Best wishes, Paul
