This remodeling process replaces about one-fifth of your skeleton every year. In childhood, more bone is added than removed, so bones grow in both size and density. In adolescence, bones stop growing in size but continue to become more dense, reaching peak mass around age 30. If the loss is greatly accelerated, osteoporosis results. Osteoporosis can occur when too much old bone is removed, when too little new bone is formed, or both, though experts do not fully understand what causes these changes.
Bones remain the same size, but the compact bone becomes thinner and the spongy bone more porous.
The drop in estrogen at menopause appears to cause bone to dissolve at a faster rate, typically in the wrist and spine. With age, however, both men and women are slower to build new bone, which affects mostly the hip. In the early stages of osteoporosis, there are often no symptoms at all. People can lose bone mass over many years but not know they have a problem until a bone breaks. As the disease progresses, small fractures may occur in the spine.