ABSTRACT
Throughout life, bone is continuously renewed. In the elderly, adequate supply of vitamin D, calcium (Ca), phosphorus, and protein are nutrients required for renewal of bone mass and function. Low supply of these nutrients can accelerate age-related bone loss. Regarding phosphorus, over the last three decades there has been more concern about the possible deleterious effect on bone metabolism of excessive rather than insufficient intake. In this chapter, we recall some fundamental aspects of phosphorus homeostasis, underscoring the essentiality of this element for maintaining many vital cellular processes during aging. In bone, phosphorus associated with Ca is deposited on the organic matrix by mechanisms involving specific osteogenic cell transporters. This mineral deposition strengthens bone mechanical resistance. The phosphorus economy 156is tightly controlled. The renal tubular reabsorption is the main controlling system. Genetic defects in this renal regulatory capacity lead to severe impairment in bone mineralization that is clinically expressed as rickets during growth and osteomalacia during adulthood. In absence of such selective renal transport defects, phosphorus depletion with hypophosphatemia is uncommon. Besides the renal controlling system, the wide phosphorus distribution in foods and the large net fractional intestinal absorption contribute to this infrequency of phosphorus depletion. Nevertheless, it can be observed in some pathologic conditions, including severe alcoholism, diabetic ketoacidosis, pulmonary infectious diseases, or myocardial infarction. In elderly patients with severe osteoporosis treated with bone anabolic agents in combination with supplemental Ca salts that reduce the intestinal phosphorus absorption, the dietary supply of phosphorus may not be sufficient to cope with the increased phosphorus needs resulting from the stimulated bone mineralization. In this situation, a mineral supplement provided as Ca-phosphorus salt could avoid the high intestinal Ca/phosphorus ratio that would worsen the imbalance between phosphorus supply and bone requirements. In the elderly, such a Ca/phosphorus supplement was shown to reduce hip and other fragility fractures.
