I have had two DEXA scans (due a third in the Autumn) and have confirmed osteopenia.
I've also had a bone profile blood test, which shows that my blood calcium level is normal. As far as I know, there is no test for showing how much calcium is retained by your bones, teeth, etc. A high blood calcium level could show that calcium isn't getting into the bones or it could be for another reason.
It hasn't been recommended that I take any supplement or medicine, apart from the normal dose of Vitamin D, which everybody is recommended to take in the Winter months. I was told that my calcium intake should be adequate, as my diet includes dairy, green leafy veg and sardines.
The reason I'm mentioning this is because I have had the tests and osteopenia confirmed, so not just guesswork. Even so, supplements haven't been recommended. Mind you, I agree with Gran22boys that, in general, GPs and other medical staff seem poorly informed about nutrition, including vitamins. I've been told different things by staff in the same practice and I often think they rely on "old wive's tales". The NHS site isn't very good either, although I find some of the information sheets from trusts and hospitals quite informative. Ignore anything issued by anybody selling anything (supplements, books, private consultations) like the plague.