Hormone therapy interferes with the standard mechanism of replacing the bone in your body, resulting in old bone being dissolved away faster than new bone replaces it. (Your body normally replaces about 10% of your bone each year.) A combination of Calcium supplements, Vitamin D3, and exercise which stresses bones can slow this process of bone loss down. Recently it's been suggested Vitamin K2 might help too, but this can't be taken by people on some blood thinners.
If you get to the point where you have osteopenia or osteoporosis (loss of calcium from the bone), you are likely to be prescribed bisphosphonates or Denosumab (which is similar) and you don't really have much choice when they become necessary. These switch off the process of your body replacing bone, which goes wrong while on hormone therapy.
I'm not on these, but one important thing is before you start on them, you need to go and have a detailed dental checkup and get anything fixed before you start. Getting tooth infections or treating tooth roots or having extractions should be avoided while on these drugs because it can cause the jaw bone around them to die.
There are various bisphosphonate drugs, and they vary from a weekly tablet through to a 6-monthly infusion.
