Robert P. Heaney, MD, John A. Creighton University Professor at Creighton University, wrote in his 2000 article "Calcium, Dairy Products and Osteoporosis," published in the Journal of the American College of Nutrition, that:

“[L]ow intakes [of calcium] predispose to development of osteoporosis by reducing achieved peak bone mass during growth and by causing or aggravating age-related bone loss later in life…high calcium intakes are recognized as protective against osteoporosis.

It is long established and well understood that milk supports growth; thus, it is evident that milk and milk products are good sources of the nutrients needed for bone development and maintenance.

One sometimes encounters arguments that the protein and sodium of milk somehow negate the potential benefit of its calcium. These speculations are based on the established fact that both protein and sodium lead to increased urinary calcium excretion. However, the negative effects of protein and sodium are observed mainly at low calcium intakes, when, with absorption already operating at an individual’s maximum, there is no possibility of increasing calcium extraction from the diet so as to offset an increment in excretory loss…

[E]ven at low calcium intakes, the ratio of the calcium in milk to its sodium and protein content is so high as to offset directly any calciuric effects; that is, even without physiological adjustment, the calcium absorbed exceeds the calcium eliminated by virtue of sodium and protein…a diet low in dairy foods means a diet that is poor in several respects beyond insufficiency of calcium.”