Dairy versus calcium carbonate in promoting peak bone mass and bone maintenance during subsequent calcium deficiency

Dairy products provide most of the calcium in the diet, but consumption of milk has declined steadily over the last six decades. We determined (1) benefits to bone formation in growing female Sprague-Dawley rats when calcium is derived from dairy versus CaCO(3) and (2) residual benefits of calcium provided by dairy to rats subsequently receiving a low-calcium diet. During growth, femurs from rats fed nonfat dry milk solids (NFDM) had 8.4% higher peak breaking force, 6.4% greater Ca content, 4.8% greater weight, 4% greater width, 1.2% greater density, 13.1% greater midshaft cortical thickness, and 16.7% greater midshaft cortical area than from rats fed CaCO(3). These effects were unrelated to differences in calcium absorption or serum IGF-1, but the NFDM group had higher rates of bone formation. If maintained on an adequate calcium diet, many of these advantages disappeared. However, rats fed adequate Ca as NFDM versus CaCO(3) during growth and subsequently switched to deficient Ca as CaCO(3) had significantly (p < 0.0001) higher femoral BMD (1.3%), total bone Ca (7.2%), Ca concentration (4.6%), and cortical thickness (9.4%) and a trend (p = 0.02) toward greater peak breaking force (17%). Thus, NFDMs improved bone measures during growth and protected bone against a subsequent period of calcium depletion compared with CaCO(3).