Lifelong calcium intake and prevention of bone fragility in the aged.

Primary prevention of osteoporosis involves achieving the full genetic potential for bone mass. Secondary prevention is concerned with protecting what bone mass a woman may have at her current age. Calcium plays an important role in both. Calcium requirement varies with stage of growth, with physiological drains (e.g., pregnancy and lactation), and with factors that influence absorption and excretory loss (e.g., gonadal hormone status and sodium and protein intakes). The evidence is strong that prevailing calcium intakes contribute to the low bone mass component of osteoporotic fragility and that increases in intake would reduce the osteoporotic fracture burden. At the same time it needs to be emphasized that bone health is a multifactorial affair and that meeting calcium requirements alone will neither guarantee optimal bone growth nor protect against bone loss if other critical factors are missing. For example, calcium affords only minimal protection against either immobilization or estrogen withdrawal bone loss. Thus, while assuring an adequate calcium intake remains a sound strategy, it cannot be considered a total preventive for osteoporosis.