A frightening divergence from this pattern sometimes occurs when bone begins to thin and get brittle much earlier in life. As the body fat level falls dangerously low, the ovaries don't make enough estrogen. Without enough estrogen, the production of new bone cannot keep up with the resorption of dying bone. It is as if a false menopause is occurring. When dying bone tissue is not replaced quickly enough, the bones become weak and porous, leading to osteoporosis, a disease of fragile bones, which leads to an increased risk of fracture.
Pictures clearly show the difference between healthy and osteoporotic bone.
Under this definition, almost half of all postmenopausal women aging normally are diagnosed as having this disease. A more realistic definition sets an age-appropriate standard for bone mass and determines what level of diminished bone mass makes someone particularly susceptible to fractures. The gravity of the problem for young athletes shows up as sports physicians see some women in their twenties who should still be building bone but who, instead, have bone density like that of women in their seventies and eighties. This bone loss is irreversible. Bone loss often progresses gradually, with no symptoms until a woman breaks a bone and is diagnosed as osteoporotic.