[Pathogenesis of postmenopausal osteoporosis]

Low peak bone mass and increased bone loss within the process of bone remodelling are the most important determinants for the manifestation of postmenopausal osteoporosis. Both are influenced during lifetime by a large number of risk factors additively leading to a critical low bone mass. Loss of bone substance and deterioration of architecture of bone tissue lead to an increased fragility of the skeleton. In this complex interactions menopausal decrease of endogenous estrogen secretion is of special importance. Decrease of estrogen induces by effects on calcitropic hormones and different local growth factors a high bone turnover with a high rate of bone loss. The resulting slight increase of serum calcium and the consequent decrease in the secretion of parathyroid hormones and activation of vitamin D in the kidneys lead to a decreased intestinal calcium absorption. In peri- and early postmenopausal women there is a large range of different degrees of bone turnover. It is unclear however, whether there are really two distinct groups of so-called rapid and slow bone losers. It remains to clarify which intrinsic mechanisms besides the risk factors are responsible for the individually different answer of calcium and bone metabolism to estrogen deficiency, which is the same in every women.