The different routes of administration and the effect of hormone replacement therapy on osteoporosis.

OBJECTIVE: To review osteoporosis, a disease characterized by low bone mass, microarchitectural deterioration of bone tissue leading to increased bone fragility and a consequent increase in fracture risk. The disorder has become a major health problem in the West, where increased life expectancy has placed new emphasis on disorders related to aging.
DESIGN: Review of selected literature. MAIN OUTCOME MEASURES: Bone mass increases rapidly in growing children and adolescents, reaching a peak in adults in their 20s and 30s. After 35 to 45 years of age, bone mass begins to decline slowly. Men lose bone mass at approximately the same rate over their lifetime; in women, however, the rate of bone loss increases dramatically after their menopause, whether it is natural or surgical. It is also important to note that bone mass in women below the age of 50 is just two thirds of that found in men. These two factors--the low initial adult bone mass and the more rapid bone loss--combine to produce a high incidence of osteoporosis in elderly women. Significant morbidity and mortality are attributed to osteoporosis-related fractures, underlining the importance of new therapeutic and preventive modalities being evaluated and applied in high-risk populations. In adult women before the onset of menopause, rates of bone formation and bone resorption are approximately equal; calcium balance is maintained, and no loss of bone mass occurs. But after menopause, although both bone formation and bone resorption rates increase, the rate of bone resorption increase more rapidly, resulting in calcium imbalance and a net loss of bone. The first goal of therapy for osteoporosis is thus the restoration of bone resorption and bone formation to premenopausal levels. Optimally, bone formation may be maintained at a slightly higher level than that of bone resorption, producing a positive calcium balance.