Everyone is different in terms of where they feel well, and 300pmol/L is the threshold recommended by Prof Studd for bone protection.
Vaginal atrophy is uncommon above around 183pmol/L (Sarrell et al 1990)
However mood and psychological symptoms can require higher estradiol levels to resolve in some women e.g. 450-800pmol/L
Other outcomes such as cardiovascular and brain health have not had protective thresholds delineated as far as I am aware.
Personally I feel well around 400pmol/L and I would not let myself get below this.
Testosterone can also help with energy, cognitive and mood symptoms and is definitely worth adding, however if someone has low estrogen (for them), our clever bodies just convert more testosterone to estradiol as the latter is more critical for health.
It's no good having a sharp mind and a great libido if the bones that hold everything up are crumbling, or your skin and genital tract are dry and atrophic, leaving you vulnerable to wounds and infections for example, so if you take testosterone in the setting of low estrogen, you are really just taking expensive estrogen as this is its metabolic fate.
