This reduced bone mass probably results from a low peak bone mass rather than from excessive bone loss. In both women and men, interestingly, a low peak bone mass may be genetically associated with premature graying of the hair. Apart from genetic factors, physiologic factors and environmental considerations are also important in putting people at risk for osteoporosis. Bone is a living tissue. It serves as a storage site for calcium as well as structural material for the skeleton.
Hormones regulate the ebb and flow of calcium in and out of bone.
Bone is constantly remodeled by the actions of two systems, the osteoclasts that remove bone and the osteoblasts that make new bone. The osteoclasts are derived from macrophages and function to digest trenches within the bone in periodic cycles of activity. These trenches are then filled in with new bone produced by osteoblasts. When the amount of bone being removed by the osteoclasts exceeds the amount put back by the osteoblasts, the bone mass is reduced and eventually becomes increasingly subject to fracture. Sex steroids, estrogen in women and testosterone in men, act to limit osteoclast function to allow as much bone to be replaced as removed.