Urinary Calcium Excretion in Human Beings

CALCIUM is the most abundant cation in human beings. The total body content averages about 25,000 mmol, or 1 kg, in a 70-kg man — virtually all of it occurring in bone.1 Perhaps the most important biochemical property of calcium is that it forms salts that are barely soluble (Fig. 1).2 The solubility of calcium monohydrogen phosphate (CaHPO4·2H20) appears to determine the precipitation of calcium phosphates from aqueous solutions; this salt then undergoes transformation to apatites [Ca10(PO4)6(OH)2 or Ca10(PO4)6CO3], which are the principal . . .