OSTEOPOROSIS

disease characterized by the thinning of bones, with a consequent tendency to sustain fractures from minor stresses. The disorder is most common in women over the age of 50 and results from disturbances of mineral metabolism and nutrition. In persons afflicted with osteoporosis, the tiny, rigid plates forming the honeycombed matrixes within bone gradually become thinner and rodlike, and the spaces between them grow larger. The bone thus becomes more porous, less dense, and less strong. These lighter and more fragile bones tend to fracture from minor traumas and stresses that ordinarily would have no ill effects. Over time the minute crush fractures that occur in the vertebrae of the spine cause the back to curve, resulting in the humped back and bent posture that can be observed in many elderly people afflicted with osteoporosis. The bones of the hip and forearm are also especially vulnerable to fractures. The other symptoms of osteoporosis are loss of height and back pain. Osteoporosis results from changes in the balance between the amount of new bone that is formed within the body and the amount of bone that is resorbed, or broken down and assimilated. The latter process occurs because calcium in the bones is regularly drawn upon to maintain the calcium that circulates in the bloodstream and is needed for normal nerve and muscle functions. When, for whatever reason, the body has insufficient other supplies of calcium to draw upon, it will draw on the calcium held within the bones, and, as the calcium reservoir in the bones decreases, bone loss ensues. In persons with osteoporosis, the rate of bone formation is normal but bone resorption is accelerated, leading to a net loss of bone mass. Bone mass in the body reaches its peak during young adulthood. Then, after a period of stability, there is a slow but steady loss of bone beginning about age 40. This bone loss occurs because, as people age, their bodies become less efficient in absorbing the calcium that is present in their diet. The lack of calcium leads to increased bone resorption. Women are subject to several additional causes of osteoporosis. First, osteoporotic vulnerability is partly dependent on the bone mass originally present; persons with larger, denser bones can lose more bone without becoming prone to fractures than can persons who had lighter bones as young adults. Since men have heavier bones to begin with than do women, their bones are still proportionally denser (and hence stronger) after the inevitable loss of bone mass due to aging. Second, women are subject to an accelerated rate of bone loss after they reach menopause, owing to the body's lack of estrogen and other sex hormones. The other common causes of osteoporosis are a simple dietary deficiency of calcium, markedly decreased physical activity, and a dietary imbalance between the amount of calcium and phosphorus ingested. Osteoporosis in later life can best be prevented by ensuring an adequate dietary intake of calcium and by supplementing one's calcium intake if necessary. Moderate physical exercise is also useful. For women aged 40 or older, estrogen given with progesterone can act to slow the rate of bone loss, though it is not clear whether this therapy is advisable or necessary for all menopausal women. Evidence is emerging that a treatment using sodium fluoride and calcium can halt bone loss and actually stimulate the formation of new vertebral bone in osteoporotic patients.