As someone affected by Hypothyroidism and Hashimoto’s, I believe that research is severely lacking in this area, and that there is a deficit of knowledge among those who would treat us.
My cardiovascular disease was present long before my thyroid disease was diagnosed therefore I am not sure whether or not there is a causal effect in my case?
For many years I was unsatisfactorily treated with Levothyroxine alone until I convinced my Endocrinologist to let me try a wee bit of T3. She was very reluctant because of my existing heart disease but she monitored me and we agreed on 10 mcg per day (working slowly up to this dose and titrating T4 downwards). What a difference it made! I feel so much better.
Of course I would support a proposal to look into the role of T3 in the treatment of hypothyroidism however, this is a very complex area of research so not one for the faint hearted.