Higher cortisol levels reduce TSH (through the effect on the hypothalamic-pituitary system). A reduced TSH does two things:
- For those patients with working thyroid tissue, lower TSH will decrease thyroid hormone production.
- Lower TSH also reduces T4 to T3 conversion, resulting in even less T3 (active thyroid hormone)
Lower cortisol levels increase TSH. An increased TSH does two things:
- For those patients with working thyroid tissue, higher TSH will increase thyroid hormone production.
- Higher TSH also increases T4 to T3 conversion, resulting in even more T3. Studies have found that in severe cortisol deficiency, the TSH and FT3 are often high. Cortisol (HC) supplementation in these people, normalises the TSH and FT3.
We do know that cortisol and T3 are both required to increase mitochondrial energy production. So a lack of cortisol is likely to reduce T3’s effectiveness in the mitochondria. But there are probably other mechanisms at work, yet to be discovered
T3 and cortisol both need to be at good levels. Cortisol increases T3-effect, and T3 increases cortisol-effect – they are in a partnership within the cells. T3 helps to keep cortisol levels up as it stimulates the hypothalamic-pituitary system more than T4. This latter point is why thyroid medications that contain T3 help to keep cortisol levels higher. Low cortisol is very common in thyroid patients, as many have lower T3 levels during the day and in the night than they had when they were well (for reasons I have discussed in my books and in various other blog posts). For all the reasons above, it should be clear that with low cortisol, T3 does not work as effectively as it should do. High cortisol also causes problems and can reduce the effectiveness of T3 within the cells, hence thyroid patients with high cortisol often complain of feeling hypothyroid even when they appear to have reasonable FT3 levels.
However, I know of no evidence whatsoever that T3 is less able to enter cells when cortisol is low. That would require cortisol to affect the T3 transporter molecules in the cells’ membranes. There is no evidence that cortisol does this, and I do not know of any researchers who believe this (and I have spoken to some about this specifically). I stated this clearly in the first edition of Recovering with T3. I said that cortisol was not required to allow FT3 to enter the cells.
If someone comes to me and says that their FT3 level seems quite good or high, but they are not feeling well still, it simply means that there is another problem that needs to be resolved. If low cortisol is behind the problems, it can result in slightly higher FT3 due to the mechanism that I have described above.
The bottom line is that a high FT3 on a T3 combination treatment is not unusual, and this does not mean the T3 is not getting into the cells (‘pooling’ as some people call it). The T3 is still getting into the cells. The issue is simply that having enough FT3 is no guarantee that metabolism is going to work correctly. Many other things need to also be right, including the cortisol level, as T3 and cortisol work synergistically.
Cortisol does not help FT3 enter the cells. There is no evidence for cortisol having any effect on FT3 transport into the cells at all.
As I stated in the opening paragraph here, low cortisol does have some effect on raising TSH, which also increases T4 to T3 conversion. So, people whose cortisol is low may get a small amount of extra FT3 from this. But their cellular FT3 will also be a little higher too. It isn’t that the T3 cannot reach the cells.
When someone is still not feeling well, and their FT3 levels look good to high, it could be assumed that T3 is not getting into the cells. There are many reasons for metabolic rate not to be correct, including low cortisol.
However, cortisol has no bearing on the entry of FT3 into the cells. The ‘pooling’ concept may scare some patients to rush into cortisol supplementation because for many thyroid patients they have come to associate this word with low cortisol issues. Yet, there can be many reasons for thyroid treatment not working. Yes, these need to be resolved. However, the reason for thyroid treatment not working is not always low cortisol.
A good FT3 level does not mean the T3 is not available in the cells – it will be. I have written about many reasons for thyroid treatment not working properly in my latest book, The Thyroid Patients Manual. Please see:
https://paulrobinsonthyroid.com/the-thyroid-patients-manual/ for more information on the book.
If someone is on too much thyroid hormone treatment, but it is not working well, and the issue that fixes the problem is resolved, they can feel hyper-thyroid. This is not a sudden rush of FT3 into the cells – the FT3 is already there! It is simply that they were taking too much thyroid hormone to begin with. The issue that has been resolved has simply allowed the biologically active T3 to do its job. These people will need to adjust their thyroid medication and ensure that they are not taking too much. Of course, once whatever issue has been resolved the person may find that they are on the right amount of thyroid medication already or even too little still.
It is important to not rush into using synthetic cortisol (HC, Cortef, adrenal glandulars), as soon as thyroid treatment is not working and FT3 appears to be good-high. Cortisol needs to be tested fully (cortisol saliva testing and an 8:00 am morning cortisol test), and other vitamins and minerals need testing – see The Thyroid Patient’s Manual for details on these.
The word ‘Pooling’ has been used a fair amount on the Internet. However, there is no substantive evidence for any real pooling. It is just good-high FT3 levels that are not being effective, for one reason or another. It is a misleading term that different people interpret in different ways (sometimes in a rush to use hydrocortisone/HC). If I could be given $1 or £1 for every person that spoke to me and said, “I have been told I am pooling, and need to begin using hydrocortisone”, I would be a rich man. What is always important to focus on is what is stopping a treatment working, fixing it, and getting the treatment to be successful.
I hope you found this helpful.