High & Low Cortisol Effects on Thyroid Hormone, and Dispelling an Internet Myth
Higher cortisol levels reduce TSH (through the effect on the hypothalamic-pituitary system), and this reduces T4 to T3 conversion. Lower cortisol levels increase TSH. resulting in an increase in T4 to T3 conversion. 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. Low cortisol is very common in thyroid patients (for reasons I have discussed in my books and in other blog post). For all the reasons above, it should be clear that with low cortisol, T3 does not work as effectively as it should do.
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 spoke 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 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'. It is definitely worth a read. See http://recoveringwitht3.com/book/thyroid-patients-manual for more details.
If someone is on too much thyroid hormone treatment, but it isn't working well, and the issue that fixes the problem is resolved, they can feel hyper-thyroid. This isn't 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 isn't 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 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.