This Tania Smith blog describes in great detail how we respond vis-a-vis T3 production from T4 in winter, and why those on T4 with no thyroid cannot respond as well as they ought.
Winter T3 loss: Why it matters to thyroid patients
BY THYROIDPATIENTSCA on APRIL 13, 2021
Another really useful article by Tania S Smith. I do like her stuff, (cos i need pictures)
I particularly like these ones as they both show very clearly how 'healthy ' people tend to have equal or greater fT3 than fT4 (%through range), compared to T4 treated people who tend to have much higher fT4 % than fT3 (%through range)
...which to me is a perfectly logical explanation for why so many of us, even if we achieve fT3 mid range don't do very well.
We were probably used to having fT3 equal to or greater than fT4 in health (when viewed as % through range)...which from members results on this forum it seem is a rare thing to achieve from taking T4 only.
and i also found this bit thought provoking:-
"TSH can only successfully defend T3 in winter or replenish depleted T3 in illness if a person relies largely on TSH-stimulated thyroid function. This natural T3-defense mechanism is lost in a person handicapped by thyroid function loss or central hypothyroidism. To play its T3-defensive role, the TSH cannot be hindered from rising above reference, if need be, to enrich the T3 side of its secretion ratio. Hindrances to TSH rising and stimulating a healthy thyroid gland fragment include T4 thyroid hormone dosing, severe illness, and calorie restriction. In people whose TSH is hindered from defending T3, circulating levels of T3 are vulnerable to loss (Read more: “The thyroid gland is a T3 shield. Defend the unshielded.”)
The hormone level that the healthy HPT axis defends and optimizes to the individual (FT3) should be the hormone(s) we defend and optimize during thyroid therapy. This is the logical way to defend health in people whose HPT axis can no longer defend or optimize FT3 due to thyroid function loss."
I've never really though of it in as simple a way as this before....ie. it is the act of keeping our fT4 permanently topped up (and therefore our TSH down) that stops our TSH from fluctuating naturally when needed to prioritise T3 production.
.........Probably a gross oversimplification, but it made me think anyway.
Ahhh thankyou D. This makes complete sense to me.
\"T4 can attach to receptors limiting the space for T3 to get in\"
Importance of T3 testing
