It is an all-too-familiar scenario. The elderly woman pulls herself out of bed, reaches for the night table for support, and misses. She falls, landing on her hip. A younger woman would pull herself up, and maybe ache for a few minutes and develop a black and blue mark by the next day. But the 80-year-old, with weakened, brittle bones, suffers a broken hip. Each year in the United States, 200,000 senior citizens break their hips, more than 90% of the time as the result of an accident.

In osteoporosis, the skeletal system loses bone volume and mineral content. This disorder is associated with aging. Within affected bones, trabeculae are lost, and the bones develop spaces and canals. These enlarge and fill with fibrous and fatty tissues. Such bones easily fracture and may break spontaneously because they are no longer able to support body weight. For example, a person with osteoporosis may suffer a spontaneous fracture of the thigh bone (femur) at the hip or the collapse of sections of the backbone (vertebrae). Similarly, the distal portion of a forearm bone (radius) near the wrist may fracture as a result of a minor stress.

Osteoporosis causes many fractures in persons over forty-five years of age. Although it may affect either gender, it is most common in thin, light-complexioned females after menopause.

Factors that increase the risk of osteoporosis include low intake of dietary calcium and lack of physical exercise (particularly during the early growing years). However, excessively strenuous exercise in adolescence can delay puberty, which raises the risk of developing osteoporosis later in life for both sexes.

In females, declining levels of the hormone estrogen contribute to development of osteoporosis. The ovaries produce estrogen until menopause. Evidence of the estrogen-osteoporosis link comes from studies on women who have declining estrogen levels and increased risk of osteoporosis. These include young women who have had their ovaries removed; women who have anorexia nervosa (self-starvation) that stopped their menstrual cycles; and women past menopause. Drinking alcohol, smoking cigarettes, and inheriting certain genes may also increase a person's risk of developing osteoporosis.

Fortunately, osteoporosis may be prevented if steps are taken early enough. Bone mass usually peaks at about age thirty-five. Thereafter, bone loss may exceed bone formation in both males and females. To reduce such loss, people in their mid-twenties and older should take in 1,000-1,500 milligrams of calcium daily. An 8-ounce glass of nonfat milk, for example, contains about 275 milligrams of calcium. It is also recommended that people engage in exercise regularly, especially walking or jogging, in which the bones support body weight. Additionally, postmenopausal women may require estrogen replacement therapy, which should be carried out under the supervision of a physician. As a rule, women have about 30% less bone than men; after menopause, women typically lose bone mass twice as fast as men do.

Confirming osteoporosis is sometimes difficult. An X-ray film may not reveal a decrease in bone density until 20% to 30% of the bone tissue is lost. Noninvasive diagnostic techniques, however, can detect rapid changes in bone mass. These include a densitometer scanner that measures the density of wrist bones, and quantitative computed tomography, which can visualize the density of other bones.

In other cases, a physician may take a bone sample, usually from a hipbone, in order to directly assess the condition of the tissue. Such a biopsy may also be used to judge the effectiveness of treatment for bone disease.

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