How does taking thyroid hormone switch off our own hormone production?

[Mac2013]

I’m relatively new to this group and learning so much and incredibly grateful to the wealth of knowledge here. I keep reading on various posts that when we introduce thyroid hormone (via which ever med) that it does not supplement but switches off our own thyroid hormone production and I am wondering if someone can explain how this happens or refer me to further reading. Many thanks

[HealthStarDust]

I have also read this so many times on the forum, however I am not sure how accurate it is. This is as my thyroid spontaneously started producing its own hormones despite taking levothyroxine. Logically then, it doesn’t seem entirely accurate that it switches off your own thyroid production.

[tattybogle in reply to HealthStarDust]

not strictly speaking 'spontanious' in your case though HSD... 'it's your TRab wot did it'.

they are asking your thyroid to make T4 /T3 (by stimulating the TSH receptors on your thyroid) stimulating TRab act just like TSH does. your thyroid can't tell the difference.

It's not the added levo that turns off/ lowers production from the thyroid .... it's the lower TSH that added levo causes. But in your case ,despite no TSH present your thyroid is now being asked to make T4/T3 by some TRab masquerading as TSH.

[HealthStarDust in reply to tattybogle]

Thank you TG. I suppose I would understand this all much better were it not for my compromised comprehension.

[tattybogle in reply to HealthStarDust]

we'd ALL understand it a lot better if any endo's had been interested enough to start taking more comprehensive antibody tests over the last 15 yrs and we had any proper data to look at ....like you'd think they would since a) it's very interesting and b) , it's within their supposed area of specialist interest, an area wot they get paid loads of dosh to work in and try to understand...... you'd think .

honestly... it's like someone studying sea levels and recording that the sea goes up and down every day , but not bothering to show any interest in the moon... if i was paying todays endo's , i'd sack most of em for being too lazy / thick/ complacent to do their job properly.

[HealthStarDust in reply to tattybogle]

Yes. I am 100% with you on this!

Sack ‘em all!

[HealthStarDust in reply to tattybogle]

Also, it makes no sense there isn’t as much studies on antibodies as I feel there should be. Like you, I find them most fascinating.

[HealthStarDust in reply to tattybogle]

Perhaps it would be more accurate to state that levothyroxine switches off your own thyroid production by lowering your TSH, unless you have stimulating trabs?

It does not seem like a very accurate or conclusive statement (that levothyroxine lowers TSH thus switching off one’s own thyroid production) without that caveat.

[Mac2013 in reply to HealthStarDust]

🙏🏾

[helvella Administrator Thyroid UK]

In a healthy person with no thyroid issues, the pituitary will make more TSH if it detects what it thinks is insufficient thyroid hormone in the bloodstream

And, of course, it will make less TSH if it thinks there is too much thyroid hormone.

If your TSH reaches, say, 10, but your thyroid cannot produce sufficient thyroid hormone, then the TSH will remain high. And you will be hypothyroid.

If you then take sufficient thyroid hormone, your TSH will drop down to, say 1 (around what it might be in a typical healthy person).

But your thyroid will now only be receiving the stimulation of TSH at a level of 1. If your thyroid could produce sufficient thyroid hormone at this TSH level, you would never have seen TSH reach 10. But at a TSH of 1, it is unlikely that your thyroid will be stimulated to produce even as much as it had been making. And if TSH drops further (which is often needed by patients to resolve they hypothyroid symptoms), your thyroid will make even less thyroid hormone.

I don't go all the way to claiming that your thyroid will not, cannot, make any thyroid hormone at all. For myself, my long-term levothyroxine dose wouldn't be enough on its own. But I do think it is making less than it was making when my TSH was elevated. This will, as everything else, be individual.

(I've ignored lots of things - like the hypothalamus, TSH releasing hormone (TRH), etc., for the sake of simplicity.)

It would be great if we could just take a top-up dose. But I simply don't think that is viable.

You could do a thought experiment (a fantasy!) and imagine what would happen if you took a top up dose of levothyroxine - and alongside that, took sufficient TSH to ensure your own thyroid continues to make as much thyroid hormone as it can.

[GreenTealSeal]

I’m not sure this is the case for everyone tbh.

I became incredibly ill last year following advice on here that you need to work toward a FULL replacement dose of thyroxine (for me this would be around 87.5mcg)

I am ‘subclinical’ but my ft4 has always sat happily around 16-17- pushing it any further causes awful debilitating symptoms and I feel massively over medicated.

Taking 75mcg for 8 weeks pushed my ft4 over range too. (So less than my ‘full replacement’ dose)

I wonder if dosing advice is different for subclinical?

[Sparklingsunshine in reply to GreenTealSeal]

It may be different in cases of Hashis vs other causes, we are told Hashis eventually destroys the thyroid and many long term sufferers have very atropied glands, dried up husks, essentially.

These are presumably incapable of generating much if any hormone. Non autoimmune thyroids fail for other reasons but maybe still able to produce some hormone as they havent been under attack.

I had overt hypo on diagnosis, but mine isnt caused by Hashis as I've never had raised antibodies. I know its not conclusive as some Hashis patients never have antibodies. But for the sake of argument I'm assuming its not.

I've experimented in the past by dropping Levo down to 50mcg a day, to see what would happen. My TSH rose a bit, but interestingly both frees dropped like a stone and were considerably under range. So it looks like my HPT axis has left the building.

[GreenTealSeal in reply to Sparklingsunshine]

I don’t have hashis either (no antibodies, thyroid ultrasound fine) but any dose of thyroid medication makes everything worse. The higher the dose the worse I feel. It also screws up some of my sex hormones and that just adds that me feeling crummy.

I do think in some cases a ‘full replacement dose’ is not the answer.

[TSH110 in reply to Sparklingsunshine]

I understood that hashis does not render the gland to atrophy per se, that’s the case in atrophic autoimmune thyroiditis, which is quite different. Although it’s lumped in with hashis, its a different entity altogether.

According to Dr Tania Smith:

The vast majority of Hashimoto’s patients retain normal thyroid volume into old age

See:

thyroidpatients.ca/2018/12/...

If the medical profession paid more attention to thyroid antibodies we’d be far better diagnosed and served by them. But they think they are irrelevant 🙄

[HealthStarDust in reply to GreenTealSeal]

I agree with this.

It certainly messed up my sex hormones as far as I can tell (ovulation disappeared, etc.) trying to achieve a higher FT4 and FT3 and feeling more ill with it.

And, I have come across people that appear to be well on low doses such as 25mcg. As a forum we should be better at recognising everyone is different.

[tattybogle]

it not so black/ white as 'it turns it off '

the thyroid is stimulated to make and release T4/T3 by the TSH ~Thyroid Stimulating Hormone.

Thyroid hormones (T4 and T3) act on cells in the pituitary and hypothalamus ( hormone regulating centre in your brain)

TSH is produced by the pituitary in response to changes in T4 / T3 levels in the blood.

~ if T4 levels go lower then the TSH level rises (brain is 'asking' thyroid to make more T4/T3)

~ if T4 levels go higher , the TSH level lowers ( brain is 'asking' thyroid to make less T4/T3)

so when you add some T4 from levo , the higher T4 level then lowers the TSH a little ..., and as a result of lower TSH , the thyroid is asked to make less T4/T3.

but it's not a clear case of "on/ off" ~ it's a question of degree ...... if you lower the TSH a little (lets say to 2 or 3 ish) , then the thyroid will produce a little less T4/T3 than it did when the TSH was say 5 or 6ish , but it will still make 'some' , (assuming it physically can and the thyroid gland is not totally defunct already ) . .... but yes , if you lower TSH so much that it's not even measurable , then the thyroid is not being 'asked' to make any T4/T3 at all ... so it won't , (well perhaps a dribble , but nothing significant) .

if you raised the TSH again , (eg by lowering levo dose) , then the thyroid will go back to making 'some' T4/T3 of it's own (assuming it is not totally defunct)

but it's important to realise the thyroid system is very complex ....

for example , HealthStarDust happens to have some TRab antibodies that are NOT TSH, but they ACT on the TSH receptors on the thyroid in the same way as TSH does .... so her thyroid is being 'asked' to make more T4/T3 despite having no measurable TSH)

or in the case of autoimmune thyroid disease , sometimes the thyroid will release stocks of ready made T4/T3 from it's cells as a result of these cells being damaged, and not as a result of stimulation from TSH .

So there can be lots of weirdness that is hard to understand.

[Mac2013 in reply to tattybogle]

Thank you 🙏🏾

[Lottyplum in reply to tattybogle]

Please can you put this into context if thyroid removed due to large choking goitre (btw GP said was 'psychosomatic!). Surely this changes things somewhat? Thank you.

[humanbean in reply to Lottyplum]

If your thyroid has been removed one of the effects will be a reduction in your T3 output because the thyroid produces some T3. In a healthy person with a healthy thyroid the thyroid produces about 20% of your total T3 output. The remainder is produced by various organs e.g. the liver, kidneys, brain and muscle.

For more info on where T4 to T3 conversion takes place, see this link :

healthunlocked.com/thyroidu...

Edit : I should point out that doctors think that removing the thyroid has no effect on T3 production because they believe that conversion from T4 to T3 will increase and make up the difference. I don't think I've seen any evidence that this is true.

[Lottyplum in reply to humanbean]

Which has been the case for me! Even on 200 mcg Levo I still had issues with constipation and weight gain. After finding this wonderful bunch of ppl who are far more knowledgeable than any GP I know, and after 40years with no thyroid, I got myself an Endo who prescribed T3+what a difference it has made. I'm not carrying the awful bloated swimming ring round my middle a d have begun running again at age 75! Will read the link with great interest+hopefully gain more understanding of this complex condition that most GPs think can be solved by a pull - either Levo or antidepressants!!

[Mac2013 in reply to Lottyplum]

🫠👍🏻

[HealthStarDust in reply to tattybogle]

but it's important to realise the thyroid system is very complex ....

for example , HealthStarDust happens to have some TRab antibodies that are NOT TSH, but they ACT on the TSH receptors on the thyroid in the same way as TSH does .... so her thyroid is being 'asked' to make more T4/T3 despite having no measurable TSH)

Just to add for readers, I don’t know if I have the blocking or stimulating type of antibodies… yet. Therefore, I would not like to assume my thyroid is being stimulated by trabs. But, the presence of trabs (which can be stimulating or blocking or even neutral I believe) adds to the complexity of thyroid disease.

It is also important to recognise that people without thyroid disease may have thyroid antibodies and non thyroid illness affects thyroid too. So, for example, I am wondering if my thyroid is mostly fine and there is a secondary cause as to why my thyroid levels are misbehaving.

Blood tests only tell us so much and I am beginning to strongly think before treatment is started people should have scans of their thyroid first as added hormones is no fun in the park if it’s not actually needed.

[Mac2013 in reply to HealthStarDust]

🙏🏾

[Mac2013 in reply to HealthStarDust]

I developed subacute thyroiditis after being diagnosed with endometrial cancer and have always wondered if the two were somehow connected….

[HealthStarDust in reply to Mac2013]

Presumably they could be. This whole thyroid business is too complex and I imagine any illness can create a burdensome environment for the thyroid.