My docs have me on large doses of Vitamin D, calcium, etc., to help with bone density loss due to osteopenia related to failure of my thyroid/parathyroid. No indication in lab tests it's helping. I don't notice any difference in my workouts.
I take the stuff but I'm skeptical about whether it's doing any good. Once the endocrine system messes up we're pretty much slapping bandaids on a leaking dam.