Involutional bone loss, and the fracture syndromes that are designated "osteoporosis," are multifactorial phenomena. Gonadal hormone deficiency, inadequate exercise, and a multitude of lifestyle factors are involved in their pathogenesis. Calcium is important during growth, and probably up to about age 35, when peak bone mass is finally achieved. Recent controversy concerning the role of calcium in the middle-aged and elderly, arising out of population studies showing sometimes only weak calcium effects, can be resolved by recognizing the multifactorial character of involutional bone loss, and by careful attention to such details as national differences in habitual calcium intakes. Thus interpreted, metabolic, epidemiologic, and intervention studies are internally consistent, and indicate that inadequate calcium intake also makes an important contribution to involutional bone loss.
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