For stable bone density, it's the CORRECT amount of hormone replacement that
counts.  There are problems both with too much replacement (thyrotoxicity
and all that entails) and too little replacement (hypothyroid state and all
that entails).  It's the too much thyroid that gives rise to bone density
problems.
 The correct replacement amount depends upon sound clinical
assessment, more frequently if necessary, aided but not controlled by the
lab values.  Bone density also -depends upon factors other than thyroid.
For
example weight bearing exercise, calcium mineral intake, other mineral
intake, hormone including thyroid status, prednisone or corticosteroid
intake.  Bone density does not change overnight, or even in a few weeks.
It's a slow process.

One can have perfectly normal bones independent of the type or form of
thyroid replacement, so long as the correct dose is maintained.  After all,
the body has lost it's ability to make and control the making of the hormone
in the case of most hypothyroidism people, and now the "dose" is artifically
determined infrequently clinically.  This is in contrast to when we had our
thyroid glands and the hormone was controlled every day by physiological
feedback.  Levoxyl and Synthroid, and triiodothyronine (T3)  and other forms
of synthetic hormone at the correct dose does as well as "natural" life
force thyroid
extract at the right dose in maintaining health, including bone health.

T4 converts to T3.  Not the other way around.

Regarding thyrotoxicity:  My own experience is that I was not thyrotoxic
prior to going on thyroid 39 years ago.  I have been thyrotoxic (as well as
hypothyroid) many times over the course of 39 years because of inadequate
clinical management.  I've been both thyrotoxic and hypothyroid independent
of whether I was on Armour or  "synthetic"  T4 (Levoxyl or Synthroid).  None
of this mattered.  What mattered was the correct dose of the form of
replacement I was on at the time.

I'm rather athletic, a weight lifter, do heavy yard work on a regular basis
such as cut down trees, take calcium and
mineral supplements, get aerobic exercise as well, but nonetheless, I
developed osteoporosis beginning 20 years ago.  I am not on hormone
replacement because of blood clotting problems as well as two bouts with
breast cancer.  My bone endocrinologist watches my thyroid status because of
the known effect of thyrotoxicity, be it from disease or from the pill
(iatrogenic) on bone density.

The problem of docs who are afraid of prescribing thyroid for fear of some
of the symptoms of thyrotoxicity is that they are afraid to practice
medicine and to take responsibility for properly treating a person.  They
need to be equally or more afraid of undertreating a person.




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