I actually have my latest numbers for all of this. One of the most frotunate things about my duty station is I work in medical, and can have any lab done at any time, for any reason.
TSH - 2.090 ng/dL
Thyroxine Free - 1.12 mcIU/mL
Triiodothyronine - 2.770 pg/mL
All normal. Yet I do feel sluggish and tired quite often, for no reason (well maybe 1500 calories a day at 200 lbs. is the reason).
LOL, thats my whole point which everyone seems to be missing.
Your numbers are "normal" based on what? Based on the fact that there are withing the same range as a few thousand other healthy people? How does that make you normal?
What if a few years ago when you didnt feel sluggish your Triiodothyronine was at 3.1 pg/mL?
Normal for YOU is what your thyroid hormone levels have been at consistently over years when you have felt good. If your dont have data points then the current data means very little aside from the fact that your not clinically hypo/hyper thyroid. It certainly does not mean your thyrodi is functioning optimally.
Iodine is crucial for thyroid hormone production. A better way to judge if your thyroid is functioning optimally is this....
look at a list of hypo/hyper symptoms and ask yourself if you have any, especially if they started in the last few years.
take your basel metabolic temp for a few weeks to see if your average temp is below normal.
Take an iodine loading test to see if you are iodine sufficient.
If you have symptoms of hypo/hyper thyroid, especially new ones. Your BMT is low and your iodine loading test comes back below 95% then its pretty certain your thyroid could be functioning better and without supplementation it will only get worse over the years to come.
Alternatively, just start supplementing with iodine and selenium in the proper forms for a few months and see what happens.
My labs all came back normal yet I have been struggling to lose belly fat for years. In 6 months with no eating or exercise changes I dropped 3% total bodyfat all from my core and the mild hypo symptoms I had are all gone.