Magnesium is needed for calcium absorption.
All sorts of snazzy ads are touting the benefits of combo calcium and magnesium products (CalMax, coral calcium, etc).
They often say that these products are more effective than products that contain calcium alone. They suggest that magnesium is needed to boost calcium absorption.
But there's actually no proof that the magnesium/calcium combo is any more effective for preventing bone loss...or that calcium absorption is increased.