Osteoporosis is a progressive disease that causes bones to become weak, brittle, and susceptible to fracture. Bone weakness can be the result of bone loss, the failure of the body to produce new bone (either at all or at a fast enough rate), or both. Learn more about the impact osteoporosis can have on the whole body, which bones are most at risk for people with the condition, and what preventative or restorative measures can be taken.