how much T4 needed for optimum T3

[fiftyone]

Cany anyone tell me this. Does the body take as much T4 as it needs to convert to T3. Sometimes my T3 is 5.7, somemtimes 6.1 but I take exactly the same dose of levo every day. Is there a mechanism inside the body which knows how much T4 to convert, how much T3 the body needs

[BadHare]

That’s a how long is a piece of string question. 🙃

We all need different amounts. Genetics, diet, micronutrient availability, activity, weather etc will affect how much we need.

Only bad doctors consider the one size fits all approach acceptable. If you want your levels higher, check over all the micronutrients we need to make us digest, absorb, & convert T4 to T3 better.

[fiftyone in reply to BadHare]

thanks for that, but I simply want to know does my body extract as much T3 as it needs from my T4 supply. Does my body automatically know whether it needs less T3 one day than the next ? Presume it does. So long as my T4 supplies are sufficient can I forget about T3 as my body will make it as and when necessary. Am I right.

[mandyjane in reply to fiftyone]

I would presume so. I think the conversion of t4 to T3 often happens at cellular level so as cells ask for some T3 the conversion happens. I would presume therefore that if you are for example exercising the need for T3 in the cells increases and more conversion takes place. Not sure how accurate my explanation but my understanding anyway.

[helvella Administrator Thyroid UK in reply to fiftyone]

In a healthy person, their thyroid produces T4 and T3.

Approximately one third of the T4 is excreted, one third converted to reverse T3, and one third converted to T3.

In addition, many of our tissues (notably the brain) also convert T4 to T3.

There are numerous factors which affect the precise levels.

The pituitary takes in T4 from the blood and converts it to T3, and also takes in T3 from the blood. These effectively add together to adjust how much TSH the pituitary makes. Which then, in a healthy person, adjusts the amounts of thyroid hormone produced and released by the thyroid.

If you have a thyroid, not only does it produce thyroid hormones (T4 and T3), but it also converts some T4 to T3.

This is an ultra-simplified description which misses out many parts of the whole thyroid hormone processing.

But things ranging from genes, to nutrition including micronutrients (iron, selenium, many vitamins, etc.), to other diseases, to the weather, to exercise, to age, and many others, all affect each step of the processes.

When you add in thyroid disease (if the thyroid is damaged by autoimmunity, it ceases being able to produce enough T4), the variations increase further.

You cannot say, if there is enough T4 (whether from tablets or the thyroid), there will always be the right level of T3.

For example, as the thyroid becomes unable to produce enough T4 (when being destroyed), the FT3 level in the blood often rises. Mechanisms try their hardest to ensure there is enough T3 but cannot always do so.

That doctors either assume that is the case, or fail to even think that far, is half the reason there are so many posting questions here.

The widespread opinion of many of us is that you need to test TSH, FT4 and FT3 in order to know what is happening.

[Lalatoot in reply to fiftyone]

It is complicated. In theory in a healthy person the body makes and converts enough thyroid hormones on demand - TSH tells their body how much T4 etc to produce and throughout the day the body and cells in the body are converting the FT4 in T3 to use.

However we have thyroid problems so an imperfect system. If we take thyroid hormones orally then our timing of the doses along with the timings of food, drink and vitamins can affect absorption which can lower ft4. Ft4 is converted in cells and organs such as the liver to ft3. Something that affects liver function could disrupt conversion for example.

In answer to your question then - if you do not have absorption issues and if you do not have conversion issues and you are more or less symptom-free then you can assume that the T4 you administer is converting adequately throughout every day to meet the demands of your varied routines.

[BadHare in reply to fiftyone]

There’s no simply with a health condition, our hormones affect every cell in our bodies. One thing wrong in our closed endocrine system & our body goes skewiff!

In a healthy person demand is fed by supply. With someone hypothyroid, T4 intake (supply) doesn’t automatically ensure it’s converted to the amount of T3 (demand) that a person needs. Some people will produce T3 naturally, some on replacement hormones will convert better/faster/adequately depending on many factors.

Basically, there’s no one size fits all for this. I cannot guess what your body does conversion wise, I can just about manage my own. 🙃

[Angel_of_the_North in reply to fiftyone]

If all your deiodinases are working in a text book fashion and your vitamins are optimal, and you still have healthy thyroid, pituitary and hypothalamus glands, then your your body will produce the right amounts of t4 and t3 for you. Otherwise, it's impossible to say.

[Heloise]

Your adrenals have some control and seem to gauge how much T4 should either convert to FT3 or Reverse T3 according to ??? big question. You are one of the fortunate ones with an apparently good conversion and those fluctuations are perfectly normal as others have pointed out. For those with a problem, this may partly answer the question.

nahypothyroidism.org/thyroi... says:

"Alternatively, too much Reverse T3 overly inhibits T3’s ability to provide energy and oxygen to one’s cells resulting in reduced metabolic function on a cellular level. Reverse T3 and T3 compete for the same receptors throughout the body."

How the adrenals determine this safety function might be unknown as I've never heard an explanation. One thing is certain; your body is acting correctly in order for you to survive. My own opinion as a lay person is that it may be due to lack of mitochondrial function which produces ATP. They can be blocked by toxins.