Thyroid UK
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One Molecule Per Minute

One Molecule Per Minute

Every so often my mind gets taken by an idea. Like the song you can’t get out of your head, something sticks and will not fade away.

The question that has been going round my head for quite a while now is “How much thyroid hormone does each cell of the body get?” Many of us are used to thinking about people needing, say, 150 mcg of levothyroxine a day. That does not say anything interesting or useful about individual cells – it is what we need to take by mouth.

So I have at last worked it out. I took a common estimate of the number of cells in the human body (100 trillion). An estimate of the amount of T3 produced by an “average” human being (30 mcg). And have assumed that each and every cell gets exactly the same number of molecules of T3.

Of course, there are a lot of other assumptions in there – such as T3 being the only thing that counts, that every molecule of T3 does indeed get used by a single cell. This is in adults. And so on. Given all that, the numbers come out something like this:

Number of cells in human body = 100,000,000,000,000

Number of molecules of T3 produced each day = 300,000,000,000,000,000

Molecules of T3 per cell = 3,000

Seconds in a day = 86,400

How often each cell gets a molecule of T3 = 29 seconds

Allowing a bit of a fudge-factor for imperfections in the system and my working out, I don’t think you’d be too far wrong to have a mental picture that says “On average, every cell gets one molecule of thyroid hormone (in the form of T3) every minute.”

Now is that useful? Well not as far as I can think! Might qualify as Quite Interesting?

The one area that it might help is considering why some people need much higher doses than others. You can immediately split the question in two:

Does the person’s cells need faster delivery of thyroid hormone (maybe every 20 seconds)? Or is the delivery from mouth (or thyroid!) to the inside of the cell less effective?

Somehow looking at it like this makes the issue simpler in my brain.

(If you think my numbers are wrong, don’t hesitate to challenge. I could so easily have made a mistake.)


15 Replies

That's very interesting Rod!! Thank you for this information. Would that mean that body benefits more from a dose of T3 ( in form of NDT or on its own) delivered in more frequent intervals during a day? One off dose due to quite short half life of T3 would result in some sort of T3 waste perhaps. Our cells would benefit more around the dose intake and less hours later.


I really don't know.

I have seen some people (in the USA) say they love slow/controlled release T3 precisely because it avoids peaks and troughs. But I am very wary. Imagine if you took too much - and you know it is going to carry on being released for hours and hours! Perhaps once you have found a stable dose, then changing to slow release is more reasonably achievable.

Plus, I do not trust any of the slow release mechanisms - they are not renowned for smooth, reliable steady release - more of an approximation that is better than letting it all go at once. :-)

Don't get too uptight about short half life. You do have to think about the pulsatile nature of thyroid hormone release in a healthy thyroid. And the length of time that the effect of the T3 - which is much greater than a few hours.

Lots of people on T3 (on its own or with T4) or desiccated thyroid split dose but the patterns they adopt seem to be a compromise between a large number of doses and the practicality of taking them. Especially when trying to avoid food.


Yes slow release tablets.. mhmm. I am not sure if they are so reliable.

.. And yes surely the half life is the figure to give some sort of understanding of what to expect not a clear cut answer. I don't think that all T3 drops down once the certain time is gone. We still hold T3 in our body tissues and metabolism varies between tissues.

I am not sure to what extent our body cumulates T3?


The molecule consumption would of course depend on the time of the day. Evening and night time cells would consume less. Unless someone eg me has reversed biological clock.


I think night-time is when the body repairs itself and processes information etc, so it maybe uses the T3 even more then! I really don't know, but if a person has undergone a trauma to the brain for instance, they put him into an induced coma to give his body a chance to recover. Interesting...


I have noticed that if I am feeling tired at lunch-time and I take half 25 levo I feel brighter within an hour. I take 50 levo. first thing in the morning and that's generally enough but if I take 75 straight away I soon start to feel hyper. and I don't take this extra dose more than three times a week depending how much physical/mental energy I am using up. I suppose this is on my own version of slow-release.


Have you tried taking the Levo last thing at night? Levo is very slow-acting, maybe it's what you drink with the levo which helps you? Also, Levo should not really be taken with food as it inhibits uptake.

Many studies have been done which suggests that the vast majority find it more effective take at night at least 2 hours after eating. Some have even had to reduce their dosage because of it being better absorbed.

A Japanese study found that almost all medication which has a long-term effect works better taken at night. I've been trying to find that article to read it again.


Hi Marram - i have tried taking levo. at night but it wakes me up as it seems to have an almost instant effect on me. I think I must have an odd metabolism (or something!) as I have a fast reaction to most things physical, mental and spiritual. Jax


I was under the impression that T4 rather than T3 is the more important hormone to have floating about the body since 80% of the required T3 is created by the body's own tissues using T4. T4 in tablet form has a 7 day half life.


T4 is very important in its way.

But to a considerable extent it is converted to T3 before being used within cells.

The total T3 number I used includes all conversion to T3 - within the cells that convert their own T4 to T3 as well as that produced in liver, etc., which convert T4 to T3 then release it into blood stream as well as the T3 produced within the thyroid.

In very rough and ready figures, one third of T4 is lost, one third converts to rT3, and one third to T3. So the numbers work out much the same whether you consider T4 or T3 as two thirds does not get used as a hormone. At least within the accuracy of this "finger in the air" approximation.


Certainly an interesting thought to follow.


Thank you Rod - love it! Been off for a while... story and a half but connected to T3 in a good way! Will tell soon ;-)



Like numbers, so very interesting Rod, thanks.

I think I read somewhere that T3 has its own circadian rhythm but can't remember when! I feel that the amount of T3 in the cells can also vary between individuals for other reasons for example, if our cells aren't working efficiently due to blocks of toxins or lack of the correct amounts of minerals needed.

I for one am currently on a detox of chemicals and a supplement of vits and minerals and it will be interesting to see if 1) my health improves further and 2) I eventually need less T3. I will blog fully on this when I'm further into the process, as it's early days for this approach.

Keep up the brilliant work please!



Thats brilliant never thought of it all and how our cells react. But makes sence, thats why we all need different dosages. I can't tolerate the synthetic T4 T3 so take Armour thyroid. Well done for workinf it all out though!!


Thank you Rod - this is very interesting. We are all different hence probably why we need different dose. I for one know that when I'm feeling stressed I need a little more Levo and tend to increase my dose by 25 mcg for a couple of weeks and usually see a difference. By then I'm usually less stressed,tired and back on track again.

re taking the tablet at night, I have also read the research and started taking mine before bedtime, but had to go back to mornings as I was feeling very tired during the day. I currently take alternate 120 and 100 mcg and have wondered if I should split my dose during the day. I'll let you know what I decide...


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