Sounds like you have a genetic predisposition. Sorry. Still, that doesn't mean that you're definitely going to get osteoporosis, just that you have to be more careful than normal.

One other idea is that you might check for competitive inhibitors to calcium in your diet & supps. I remember reading something about Ni++ possibly being a competitive inhibitor, but I'm sure an expert could tell you more, and more specifically. Call over to LSU and see who they have doing research in the area.