This is weird. I have read a study or two in the past that explains this, but I can’t seem to find them now.
I checked my T3, T4 and TSH, and my TSH was way oversuppressed, so I cut back on my dose of T3.
Well I had been feeling exhausted, with a very very slow metabolism and a lack of motivation. Since I cut back my dose, without even trying I have lost four pounds, my metabolism seems like it’s finally working again and my energy is back.
I know someone here will have the answer, but does anyone know the scientific explanation for this and what’s happening on the cellular and molecular level?[/quote]
I’m no endocrinologist, but here’s my shot at it.
First, T3 in the cerebral cortex, brown adipose tissue, cardiac, skeletal muscle and pituitary gland is largely produced locally from T4 in the endoplasmic reticulum by an enzyme called deiodinase 2 (D2). So if your T4 is low, you may have abnormal function in these tissues due to inadequate intracellular T3 levels in these tissues. Since this reaction takes place near the nucleus, it is presumed that the T3 here is more involved in activation, translation and transcription. This may account for your symptoms. You said you had a panel done, what were the results? Have you had thyroid ablation, thyroidectomy or do you still have some natural thyroid function?
Also, if you have an excess of thyroid hormones, when the D2 converts T4 to T3, it may convert it instead into something called reverse T3 (rT3). rT3 is not active. I would suspect the tissues identified above would also be susceptible to this effect.
Then again, I could be completely full of it. Yo Momma seems to have a great handle on biochemistry and physiology. I’d ask her for an opinion.
This is my best guess. All this came from Williams Textbook of Endocrinology, 10th ed.