From what I understand, magnesium plays an important role in calcium utilization and retention. Below are some links I found when Googling for "calcium magnesium bone density". http://www.jrussellshealth.com/osteo.html http://www.drrobinmayfield.com/newsletters/newsletter-9.html http://courses.washington.edu/bonephys/opcalcium.html Make sure your magnesium intake matches your calcium intake, make sure both are not too high, and make sure you get enough sun or some other source of Vitamin D. -Tad