EFFECTS OF AGING ON THE SKELETAL SYSTEM AND JOINTS
The most significant age-related changes in the skeletal system affect the joints as well as the quality and quantity of bone matrix. The bone matrix in an older bone is more brittle than in a younger bone because decreased collagen production results in relatively more mineral and less collagen fibers. With aging, the amount of matrix also decreases because the rate of matrix formation by osteoblasts becomes slower than the rate of matrix breakdown by osteoclasts.
Bone mass is at its highest around age 30, and men generally have denser bones than women because of the effects of testoster-one and greater body weight. Race and ethnicity also affect bone mass. African-Americans and Latinos have higher bone masses than caucasians and Asians. After age 35, both men and women experience a loss of bone of 0.3–0.5% a year. This loss can increase 10-fold in women after menopause, when they can lose bone mass at a rate of 3–5% a year for approximately 5–7 years (see Systems Pathology, “Osteoporosis”).
Significant loss of bone increases the likelihood of bone frac-tures. For example, loss of trabeculae greatly increases the risk of fractures of the vertebrae. In addition, loss of bone and the resulting fractures can cause deformity, loss of height, pain, and stiffness. Loss of bone from the jaws can also lead to tooth loss.
A number of changes occur within many joints as a person ages. Changes in synovial joints have the greatest effect and often present major problems for elderly people. With use, the cartilage covering articular surfaces can wear down.
When a person is young, production of new, resilient matrix compensates for the wear. As a person ages, the rate of replacement declines, and the matrix becomes more rigid, thus adding to its rate of wear. The production rate of lubricating synovial fluid also declines with age, further contributing to the wear of the articular car-tilage. Many people also experience arthritis, an inflammatory degeneration of the joints, with advancing age. In addition, the ligaments and tendons surrounding a joint shorten and become less flexible with age, resulting in decreased range of motion. Furthermore, many older people are less physically active, which causes the joints to become less flexible and decreases their range of motion.
The most effective preventative measure against the effects of aging on the skeletal system is the combination of increasing physical activity and taking dietary calcium and vitamin D supple-ments. Intensive exercise can even reverse loss of bone matrix.