Any truth in this about tsh t4 and t3

[130396]

Hi

I’ve just read that if you are on combo and have low tsh that if you increase Levo it will just revert to RT3.

Even if Ft4 is low and ft3 is low too.

[Marz]

Could you post a link to the source - thanks. 😊

[shaws Administrator]

I don't think this is true as researchers have shown that many recover their health on a combinationof T4/T3. This is a link which may be a better explanation excerpt:

Conversion of T4 to T3 and Reverse-T3: A Summary

The thyroid gland secretes mostly T4 and very little T3. Most of the T3 that drives cell metabolism is produced by action of the enzyme named 5'-deiodinase, which converts T4 to T3. (We pronounce the "5'-" as "five-prime.") Without this conversion of T4 to T3, cells have too little T3 to maintain normal metabolism; metabolism then slows down. T3, therefore, is the metabolically active thyroid hormone. For the most part, T4 is metabolically inactive. T4 "drives" metabolism only after the deiodinase enzyme converts it to T3.

Another enzyme called 5-deiodinase continually converts some T4 to reverse-T3. Reverse-T3 does not stimulate metabolism. It is produced as a way to help clear some T4 from the body.

web.archive.org/web/2010103...

[Clutter]

130396,

No, that's incorrect. T4 converts to T3 and rT3. If you have high FT4 and increase Levothyroxine then rT3 may increase to clear the T4. rT3 is a brake on over converting T4 to T3 and causing hyperthyroidism.

[radd]

130396,

A small amount of RT3 is healthy as balances T3 by stopping us from getting hyper and helping to clear unused T4 from the body.

An increase in Levo will not “just” revert to RT3. There has to be a cause.

Causes of elevated RT3 is an excess or build up of T4 that is not being converted to T3. Reasons for this could be high cortisol levels (directly as can inhibit the 5-deiodinase enzyme used for T4 - T3 convertion ), and indirectly low cortisol, nutritional deficiencies (such as selenium, zinc, etc), low sex hormones or elevated oestrogen, low iron, poor diet, insufficient carbs & fats, blood sugar issues, blah, blah, blah …… Also inflammation (common in Hashi sufferers).

Some people require a low TSH level to achieve well-being but as long as thyroid hormones are converting & within range you should not get elevated RT3.

[Angel_of_the_North]

Some people will convert what their body considers to be excess t4 to rT3 very quickly, but others don't. rT3 is converted to T2 and used by the body, so it is not necessarily a bad thing. It's usual to have low TSH and low to mid range free t4 when taking T3. If you are taking T3 because of poor conversion it makes sense to raise T3, not t4, to increase free T3 levels. If you are getting a regular supply of t3, you don't need to store as much t4.

[130396]

Thank you all very much for your responses