Osteoporosis, bone condition characterized by a decrease in density, resulting in bones that are more porous and more easily fractured than normal bones. Fractures of the wrist, spine, and hip are most common; however, all bones can be affected. Osteoporosis primarily affects women, who account for nearly 80 percent of all cases. White and Asian women are the most susceptible, but women of other races are also at considerable risk. Other risk factors include low calcium intake, a thin build, inadequate physical activity, certain drugs, such as corticosteroids, cigarette smoking, alcohol, and a family history of the disease.

The most common form of the disease, primary osteoporosis, includes postmenopausal, or estrogen-deficient, osteoporosis (Type I), which is observed in women whose ovaries have ceased to produce the hormone estrogen; age-related osteoporosis (Type II), which affects those over the age of 70; and idiopathic osteoporosis, a rare disorder of unknown cause that affects premenopausal women and men who are middle-aged or younger. Secondary osteoporosis may be caused by bone disuse as a result of paralysis or other conditions, including weightlessness in space; endocrine and nutritional disorders, including anorexia nervosa; specific disease processes; and certain drug therapies.

Recent research has shown that the development of osteoporosis is also related to a gene that determines the type of vitamin D receptor (VDR) a person inherits. The VDR gene exists in two forms, one of which produces a receptor that stores calcium more efficiently than the other. People who inherit two copies of the more efficient VDR gene develop high bone densities. Those who inherit two copies of the less efficient gene have somewhat less strong bones.

While there is currently no cure for osteoporosis, it is preventable in most people. Preventive measures include maintaining a balanced diet rich in calcium and vitamin D, weight-bearing exercise, and avoiding smoking and excessive alcohol. Hormone replacement therapy can be used to prevent and treat osteoporosis. Drugs used in treatment include raloxifene, calcitonin, and alendronate. To monitor a patient’s response to treatment, many physicians administer bone scans to determine bone density one or two times a year.

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