In Reply.—We do not believe that BMC and total body calcium are comparable, nor are they intended to be. Bone mineral content in adults is highly correlated to total body calcium in cross-sectional studies in which there is no longitudinal bone growth component to total body calcium.1 During growth, BMC increases at the diaphysis due to increased physical mineral density (grams per cubic centimeter) and by growth in width and cortical thickness at the measurement site. Total body calcium includes not only diaphysis but also other sites from diaphysis to epiphysis. Consequently, total body calcium increases as a function not only of increased mineral density, bone width, and cortical thickness but also of longitudinal bone growth.
With reference to what BMC is and how it can be related to total body weight, BMC is a "linear density" that is the equivalent of grams of calcium per length of