hi, awfultruth.
When trying to determine why some on anabolic treatment had lower response numbers by dxa, two associative factors were found. Individuals who hadn't taken bisphosphonates and individuals who hadn't taken vitamin d, had the best response numbers. Associative factors are determined by self-reportage and by the simple numbering ( meaning oh, these ten didn't have a good response and they are the same ten who report taking vitamin D daily in the prior years). These associative reports aren't as reliable (or interesting as) mechanism of action factors.
Later tracking indicated that those low response bisphosphonated, D'd patients had equal response in less than but close to 2 years of anabolic treatment.
Mechanism of action were later determined for bishphosphonate use. The drug clads the bone for many years preventing the remodeling effect of osteoblasts as well as osteoclasts.
Mechanism of action for D seems to be (someone probably knows for sure) the greater absorption of calcium from the intestine. The parathyroid meds tested work by pulsed flooding of the serum with calcium followed by reduced calcium in the serum, though it is subsequent effect that increases BMD.
Even if this is completely clear (let me know), it may not be completely right. Even the research is slightly speculative as we discover when further research reverses these concept. The part I trust most are the mechanism of action, but even those can be are overturned because of misinterpretation.
Bless our researchers!