I had a lecture in medical school from an endocrinologist that specialized in osteoporosis (Ugis Gruntmanis, an endocrinologist at UT Southwestern). He said we all need to be taking calcium supplements anyway (unless you drink 6 glasses of milk a day), but if you have low testosterone, you definitely need to be on calcium.
Apparently your bones increase in density until you’re 30 and then gradually decrease for the rest of your life. If you have low testosterone, it decreases much more rapidly.
Sorry if this has already been posted.