Calcium and Phosphorus

Abstract

Calcium is the most abundant electrolyte in the human body, and in healthy adults, accounts for about 2%, or 1,300 g, of body weight. Approximately 99% of body calcium is in the skeleton mainly in the form of hydroxy- apatite crystals [Ca10(PO4)6(OH)2]; the remainder is in teeth, soft tissue, and extracellular fluid. By contrast, at birth calcium accounts for only about 0.9% of body weight (1). From birth to approximately 20 years of age, when the skeleton reaches its full size and density, calcium content increases by some 40-fold (2). During this period, the increase in skeletal weight and calcium content requires the net retention ofabout 150–200 mg ofcalcium per day. Thus, in growing individuals, calcium balance must be positive to meet the needs of skeletal growth and consolidation. In adults, calcium balance is zero after peak bone mass is attained and becomes slightly negative as bone is slowly lost with aging. Calcium