Osteoporosis is the weakening of bones in the body. It is caused by lack of calcium deposited in the bones. This lack of calcium causes the bones to become brittle, so they break easily. Some side effects are limping. Some symptoms late in the disease include pain in the bones, living in a wheelchair (as a result of), and lower back pain due to spinal bone fractures. Elderly people are more likely to develop osteoporosis than younger people. The amount of calcium in the bones decreases as a person gets older.