Etiology of primary osteoporosis: an hypothesis.

By convention, osteoporosis has been described in two categories: 1) primary (involutional or postmenopausal), and 2) secondary, in association with a wide variety of pathologic disorders. Primary osteoporosis is the ultimate consequence of progressive bone loss, which starts in the middle of the fourth decade. Given the apt name of "adult bone loss," it is considered to be a universal phenomenon in that it afflicts all people of all races and both sexes. However, careful analysis of past studies generates evidence that not every person of advanced age loses bone. The etiology of "adult bone loss," and thus of primary osteoporosis, is conceded to be unknown or at least controversial. Nevertheless, the complex dependencies of bone metabolism on the functional integrity of major organ systems imply a multifactorial etiology. The age-related progressive declines in functional reserves of major organ systems may indicate that primary osteoporosis evolves secondarily to a protracted suboptimal metabolic support of bone remodeling. Further confirmation of this hypothesis may have important implications for the prophylactic management of primary osteoporosis.