I'm reading articles and one says that a normal thyroid contains 200mcg T4 to 15mcg of T3, another states that the ratio is 20/1 which would be 200 to 10 but what I was wondering is if these amounts are the total released throughout the day or what is there at any given time? This question has already been asked I'm sure and edysia is having a nap so I can't ask her and I'm having a brainfart. Does any of this make sense? I need a lie down...
Is 10 or 15 MCG ALL THAT HUMAN BODY of an individual with healthy thyroid RECEIVES DURING A DAY?? If yes why people taking NDT or t3 at much higher amounts than 15 mcg do not go hyper straight away?
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Tony63
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Tony, I don't expect you to read the fine print but there is a huge variety of factors involved in converting T4 to free T3 and if you scan these paragraphs even weight has an impact. But, of course, we hypothyroids are adding exogenous T4 which may not have much to do with T3 if we are not converting well. I'm not sure there is anything meaningful from either of those ratios for practical purposes. Maybe the potency ratio of 4 to 1 is more relevant. I had read quite a long time ago that the average production of T4 is 325 mcg. which would make the necessary T3. higher. Where did you find that 200 mcg. was normal?
The amount of T3 coming from the thyroid is only one part of the picture.
Some T3 indeed comes directly from the thyroid into the blood stream.
Some comes from the T4 which gets converted into T3 in the liver.
Some comes from other organs such as kidneys where some T4 gets converted into T3 and then gets back into the bloodstream. There is uncertainty as to which types of tissue do this but you can include kidneys and, maybe, skeletal muscle.
Some is locally converted from T4 and used in many types of body tissue such as hair follicles, possibly the brain.
Also, taking a medicine is a million miles away from using it up in the cells of the body. Start with imperfect absorption. Go on with various pathways which might cause it to be made unavailable. For example, excessively fast conversion from T3 to T2 could end up meaning that more T3 is required than in others.
Sometimes it is suggested that, very very approximately, one third of T4 gets converted to T3, one third to rT3 and one third excreted as sulphate or glucoronidated.
Thyroid hormone levels do vary through the day/night. They are released in a pulsatile fashion - that is, not continuously, but probably a number of times a day. These factors are likely to vary between people, and especially between healthy and those who are ill thyroid issues.
In the normal person its generally reckoned that about 20% of circulating T3 comes direct from the thyroid gland and the rest is converted from T4 in the tissues This is roughly mirrored by the ratio of free T3 to free T4 which is about 1/3 to 1/4 (T3 is slightly less strongly bound on to its circulating proteins than is T4). The exact ratio of T3/T4 made directly by the gland will differ from person to person and in different physiological states. For example, in hypothyroidism the ratio can be as low as 1 to 1/2 because the body is desperately trying to maintain T3 levels in the face of a failing gland. When a hypothyroid person takes T4 only, the ratio can fall to 1/5 or less, because you require more T4 to get a given T3 level. In a hyperthyroid person, the ratio can also be lower, simply because the body is converting T4 to T3 too much. So, any answer can't be definitive but depends on the circumstances.
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