calcium supplement with bone mets?

While I was on treatment for the mets I took Fosamax, then it was the weekly version.
After reaching complete response, I have been maintained on Zometa and am instructed to take a calcium supplement along with this as my analysis tends to be just below normal without it.
The nutritionist at my cancer center said the reason is that the Zometa grabs calcium from my blood supply and pushes it into my bones. So my bones get stronger, but we need calcium in other places in our bodies.