Preventative treatment of involutional osteoporosis

Abstract

The ultimate aim of prevention and treatment of osteoporosis is the prevention of bone fractures. Since 80% of fractures can be explained by reductions in bone mass, not only is inhibition of reduction in bone mass extremely important but it is also useful as an index for the evaluation of preventive therapeutic effects. Bone mass is reduced with aging, but the degree of reduction varies. Bone mass generally reaches its peak level in the 30s and 40s and decreases thereafter. There is a group, the fast loser group, in which loss of bone mass is rapid after menopause with a correspondingly increased risk for developing osteoporosis. There is also a group in which the maximum bone mass shows low peak levels and this group can be considered to be at increased risk for osteoporosis. Since there are fast losers and normal losers, it is very important that fast losers be identified at an early stage so that preventative measures can be taken, since treatment is difficult once bone mass has gone below the fracture threshold level. Once fast losers have been identified, the next step is determining the best method of treatment. It is well known that osteoporosis is caused by an imbalance in bone metabolism, i.e., an uncoupling of bone resorption and formation. From the standpoint of bone metabolism, the disease can be divided into two types: the high turnover type and the low turnover type. In the high turnover type, the rates of both bone resorption and formation are accelerated. However, since bone resorption exceeds bone formation, this leads to a reduction in bone mass. In the other group, even though the rates of bone resorption and formation are low, the rate of bone resorption exceeds formation so the bone mass is reduced. Most cases of postmenopausal osteoporosis are of the high turnover type. Many cases of senile osteoporosis are of the low turnover type, and this is considered to be caused by the decreased activity of osteoblasts associated with aging. It is not clear whether or not the high or low turnover types represent different forms of the disease with different etiologies or simply represent different stages of the same disease, as classification of the disease into these two types from the standpoint of bone turnover is very important when determining the appropriate method of treatment. In conclusion, in the high turnover type, the most effective means of treatment is to suppress bone resorption by giving antiresorbers. However, in the low metabolic turnover type, drugs that increase the rate of bone formation are recommended.