[Etiology of osteoporosis -decrease of bone mineral density and deterioration of bone quality-].

In osteoporosis, the risk of fracture is influenced by decrease of bone mineral density and deterioration of bone quality. The latter includes deterioration of the material and structural properties of bone. These changes arise from the influence of changes in hormonal balance, aging, changes in mechanical stress, lifestyle-related diseases, etc. on bone absorption and bone formation as the coupled functions of osteoclasts and osteoblasts. Deterioration of bone quality occurs at various levels ranging from the molecular to the tissue level, or even at the individual level, and leads to an increased fracture risk. Evaluating fracture risk on the basis of a sound understanding of the various etiologies of osteoporosis is important when treating osteoporosis.