Bones and Joints

As people age, bones tend to become less dense. Thus, bones become weaker and more likely to break. In women, loss of bone density speeds up after menopause.

Bones become less dense partly because the amount of calcium they contain decreases. Part of the reason is that less calcium is absorbed in the digestive tract and levels of vitamin D (which helps the body use calcium) decrease slightly. Calcium is the main mineral that gives bones strength. Certain bones are weakened more than others. Those most affected include the end of the thighbone (femur) at the hip, the ends of the arm bones (radius and ulna) at the wrist, and the bones of the spine (vertebrae).

In the center of bones is bone marrow, where most blood cells are produced. As people age, the amount of bone marrow decreases. Therefore, fewer blood cells are produced. Even with this decrease, the bone marrow can usually produce enough blood cells throughout life. Problems may occur when the need for blood cells is greatly increased—for example, when anemia or an infection develops or bleeding occurs. In such cases, bone marrow is less able to increase its production of blood cells in response to the body's needs.

As people age, the cartilage that lines the joints tends to thin. The surfaces of a joint may not slide over each other as well as they used to, and the joint may be slightly more susceptible to injury. Repeated injury or the lifelong use of joints often leads to osteoarthritis, which is one of the most common disorders of later life.

Ligaments, which bind joints together, tend to become less elastic as people age, making joints feel tight or stiff. This change results from chemical changes in the proteins that make up the ligaments. Consequently, most people become less flexible as they age. Ligaments tend to tear more easily, and when they tear, they heal more slowly.