Does too much T3 cause RT3?

[guysgrams]

I was viewing posts on another site that is specific to thyroid issues and a poster stated that too much T3 will cause RT3. I have never ever heard that, in fact much the opposite. Anyone else ever heard or read that anywhere?

[shaws Administrator]

I take T3 only. T4 (levothyroxine) converts to RT3 and then into T3 as far as I know. I think sometimes that rumours abound for some unknown reason.

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

[diogenes Remembering]

No; too much T4 will. T3 can't be converted to rT3, but to T2 and T1. Only T4 can produce rT3 as a drain to remove excess.

[Angel_of_the_North]

No. Rt3 is made from T4 and is eventually converted to T2 and used in the body

[jimh111]

Type-1 deiodinase produces equimolar quantities of T3 and rT3, it is up-regulated by high fT4 levels and other causes such as non-thyroidal illness. Also high T3 promotes type-3 deiodinase (T4 -0> rT3 and T3 ->T2). Type-2 deiodinase produces T3 only and is up-regulated by low hormone levels. So, as noted in the above resonses rT3 can only come from T4.

[guysgrams]

Thanks all for your responses!