Hi marye: You are correct on the ratio of calcium to magnesium, and frankly I've never heard that you can't take the two together, but that makes me wonder if your nurse knows something I don't; are you taking any meds that shouldn't be taken with magnesium? I would go back to the Dr and Nurse and ask specifically what they are referring to. Many multiple vitamins and calcium tabs contain magnesium so I'm confused from her statement. If you could get more info that would probably explain the issue. Your exercise routine sounds great so as long as you can keep that up that should help a lot. As far as the brittle bone issue goes, here is an article from the New York Times that explains it, and really how rare it is considering the stats on it. http://www.nytimes.com/2008/07/15/health/15well.html?_r=1&ex=1216785600&en=02dd6c110b1febbe&ei=5070&emc=eta1&oref=slogin I my opinion I don't think your osteoblasts have stopped working completely, but wonder why you might think they have. Good Luck, sorry if I couldn't give you a difinitive answer.