Why does the thyroid produce T3?

[tcpace]

As we all know, the thyroid produces T4 and T3. Given that the body converts T4 to T3, why does the thyroid produce T3? I once asked Prof Weetman this - he admitted he didn't know.

[SlowDragon Administrator]

Perhaps because the heart and brain both need good, steady supply of T3

Pity he still doesn’t admit many thyroid patients can’t regain their health on T4 mono therapy

[tcpace in reply to SlowDragon]

Makes sense but what about someone who has had a full thyroidectomy and has been put on T4 monotherapy? The only T3 available in that case would be T4-derived T3.

[Brightness14 in reply to tcpace]

Yes that's why they need to know their conversion rate and the FT3 blood test results.

Some people are on too low a dose of Levo also some do not convert to T3 easily.

[SlowDragon Administrator in reply to tcpace]

And is frequently Ft3 is then insufficient

Resulting in high Ft4, low or suppressed TSH and LOW Ft3

First step is to test and improve and maintain vitamin D, folate, B12 and ferritin at optimal levels

This can/may improve conversion rate of Ft4 to Ft3

Similarly gluten free/dairy free often helps with autoimmune thyroid

But many, many people still eventually need the addition of T3 prescribed alongside levothyroxine to improve low Ft3

[helvella Administrator]

I think there are some things that, at our present level of understanding, we have to say are as they are because that's how it works!

A lot of how the thyroid system works is inherited not just from pre-humans, from ape family, but all the way back across all animals with backbones. And there are even elements of thyroid in more primitive animals.

The details vary across genera, across species. But what we have in common is quite astonishing.

And the fundamental chemical processes of making T4 and T3 in the thyroid are very much in step with each other. Just one step different, really.

If we were able to look into the far future, maybe post-human descendant thyroids would develop to not produce T3? We'll obviously never know.

But we have to consider that there are two strands to our conversion of T4 to T3. Part is that many cells can convert T4 to T3 for use within that cell. The other part is that some cells in some organs convert T4 to T3 which then gets out into the bloodstream and passed on to other cells.

All we have to suggest is that we need more T3 than can get converted and released into the bloodstream.

Obviously some people without any thyroid tissue at all do OK on levothyroxine monotherapy. So the thyroid making T3 is not an absolute requirement for life.

But who is to say they wouldn't do better with at least some T3?

[Rapunzel in reply to helvella]

But who is to say they wouldn't do better with at least some T3?

Prof Weetman

[TSH110 in reply to helvella]

I don’t believe in a t4 only thyroid not now, and not any time in the future that would require a total redesign by nature from the primordial soup so a few billion years of work if it even could be done. If it could nature would surely have some prototypes and I bet they were evolutionary dead ends if they ever occurred

My adventures with t4 only were hideous it could not even be described as a life let alone a life worth living, we’d all loose the will to live with a t4 only thyroid, extinction of all life forms would be guaranteed - organisms not fit for purpose

do the t4 only takers really do well on it? Isn’t there a growing amount of evidence that it is not good for health and it causes problems. Nature didn’t put T3 there for a joke and lack of was is no laughing matter, in my case anyway.

[pennyannie]

The thyroid also produces trace elements of T1. T2 and calcitonin - and logic tells me if you have lost your thyroid through a medical intervention it makes sense to try and replace like with like :

The body is unique and nothing is wasted and everything there for a reason.

I have had RAI thyroid ablation and self medicate with Natural Desiccated Thyroid which is derived from pig thyroid, dried and ground down into tablets referred to as grains.

Each grain contains trace elements of T1. T2 and calcitonin + a measure of T3 and a measure of T4 and the fullest of all the thyroid hormone replacement options.

[TSH110 in reply to pennyannie]

they always claim they do nothing but now they have found T2 plays a role in mitochondria so who knows if they are used or not but like you I suspect they are important or why would the thyroid waste effort in producing them. I take my NDT sublingually just in case some calcitonin gets through. Nature is a far better inventor than the white coats she’s had millions of years of practice and been pretty darn successful everything has a thyroid of some sort but the men in white coats will claim it’s all superfluous and they know better. That’s why we all suffer on t4 monotherapy - all down to their arrogance and misplaced sense of entitlement but they hardly get any thyroid disorder so don’t suffer the consequences of their actions

[helvella Administrator in reply to TSH110]

I'm quite sure T2 is vital. But in the same way that many other biochemical pathways work - as ordinary step-by-step processes.

Whether it is sensible or useful to swallow T2 is another matter.

[TSH110 in reply to helvella]

well I’m swallowing mine - I find it’s pretty useful but it could be the other stuff in it of course 😁

I always remember feeling warm for the first time in decades (bar the hot flushes) when I took NDT I bet that’s what T2 does, warms you up as mitochondria are the powerhouses of the body and are important in body temperature regulation. One day they’ll find the evidence to back me up!

[pennyannie in reply to TSH110]

I guess if a ' white coat ' has a thyroid problem they likely could become a very good specialist in this sector and become a ' bow tie ' endocrinologist.

[TSH110 in reply to pennyannie]

they should use a bow tie icon on the thyroid U.K. endo list to indicate it!

[jimh111]

toYou could ask a different question - why do we have circulating T3 and locally derived and regulated T3?Some tissues such as the brain and brown fat get most of their T3 from conversion of T4, and maintain different T3 concentrations to blood T3. This local conversion (type 2 deiodinase or D2) is also the major source of circulating T3.

As an example brown fat will generate high T3 levels on exposure to cold.

Other tissues are happy to make do with T3 from circulation, whether is comes from D2, D1 or the thyroid).

T3 requirements for various tissues vary according to factors such as temperature, fight or flight and illness. Thyroid hormone supply is subject to thyroid disease and iodine supply.

The pituitary responds to low thyroid hormone by raising TSH which stimulates the thyroid to secrete more hormone and proportionally more T3. TSH also stimulates more D2 activity in crucial organs such as the brain. Thus conserving T3 action in vital organs.

When thyroid hormone levels are too high the pituitary attempts to shut down thyroidal secretion by lowering TSH. This also reduces D2 activity. High hormone levels also increase D3 which converts T3 to T2 and D1 which converts T4 to T3 and reverse T3 thus reducing the availability of T3.

This exquisite system maintains good T3 levels in individual tissues during large changes in supply and demand. Circulating T3 from the thyroid us part of this system.

If someone has no thyroid and gets only T4 the system is out of balance, to achieve normal circulating T3 they need a higher fT4 and lower TSH. This will disrupt local T3 levels in organs dependent on D2 activity such as the brain. This effect is fortunately minor and only really affects those with the DIO2 polymorphism inherited from both parents with a minor reduction in cognitive ability.

Of greater concern is that higher normal fT4 levels are associated with cancer and cardiac problems.

[TSH110]

I find there’s rather a lot about the thyroid endocrinologists don’t know .

It’s made because it’s imperative for health and it allows the body’s endless efforts to keep free t3 in the blood between every close parameters to succeed and keep everything functioning correctly

This explains it really well:

thyroidpatients.ca/2020/08/...

[Sallybones]

the body seems overly complicated at times, shame the middleman (T4) isn't cut out and T3 is just delivered as required!

Sorry just my out of the box thinking. I'm having a baaaad day!

[helvella Administrator in reply to Sallybones]

But T4 in the bloodstream acts as a reservoir of a (relatively) safe substance.

If we had only T3 then, as soon as we start to use it up, it needs topping up. With T4, we can have much more ready to be converted to T3 as and when needed to maintain the T3 level. And our bodies can more readily ensure that different tissues are maintained with the different T3 levels they need.

However, if all the mechanisms that control and influence conversion are not working optimally, that whole process doesn't work properly.

[Sallybones in reply to helvella]

II get you helleva. I'm being a bit tongue in cheek really. Just a steady stream would be nice. Wishfull thinking

[helvella Administrator in reply to Sallybones]

Yes - but sometimes I reply because discussing helps.

My ideas about thyroid all come from that direction.

In the "primordial soup" (I know the term is not much appreciated these days), there were iodide ions. When ultra-primitive living organisms came into being, they had to manage the various things in the soup. And iodide ions are a pretty serious problem because if allowed to stay fairly free they could disrupt many other chemical processes.

The first step was when some other compound could react with the iodide to form a stable molecule. If that other compound had been tyrosine (a basic amino acid), that is almost literally half-way to thyroid hormone. The organism found that it could make iodide safe by reacting with tyrosine to form what we now call MIT (monoiodotyrosine) or DIT (dioiodotyrosine). And kept these in a special compartment.

When the organisms had fairly short lives, that was sufficient. But as lives lengthened, the amount stored increased. Which was a problem because you can't keep storing more and more indefinitely.

Eventually, the organisms managed to fuse two DITs together, to form T4, or a DIT and a MIT to form T3. Which provided a safer pathway - and, eventually, were used for various purposes.

That is, thyroid hormone started as a safe storage. But, in time, those substances were able to be used in other ways and that is how we end up where we are.

(Should be published under Ladybird, Janet and John, or My First imprints. Or, maybe. "Fanciful Notions"?)

[Sallybones in reply to helvella]

thats a really intersting read. I do like to know how things work.

[helvella Administrator in reply to Sallybones]

Just don't take it as "the truth"!

[jimh111 in reply to Sallybones]

Many tissues require different levels of T3 which they regulate. So if they just took T3 from the blood they couldn't do this.

[tattybogle]

The amount of T3 produced by the thyroid is infinitely adjustable in response to different situations ,,presumably this ability to vary the proportion of 'ready made' (instantly available) T3 forms an important part of the mechanism which maintains a stable T3 level for as long as possible under all circumstances , even in 'emergencies' .

when the thyroid is failing, T3 is the last thing to change and go low .

eg if T4 levels go too low, the TSH rises, which prompts the thyroid to make a greater proportion of T3 to T4 ~ protecting the level of T3 for as long as possible .

Protecting the T3 like this would be harder for the body to do if the thyroid didn't make any readymade T3 and could not adjust the amount in response to challenging circumstances.