AGE-RELATED BONE LOSS AND SENILE OSTEOPOROSIS - EVIDENCE FOR BOTH SECONDARY HYPERPARATHYROIDISM AND SKELETAL GROWTH-FACTOR DEFICIENCY IN THE ELDERLY

Aging is characterized by a decrease in bone volume, implying that net bone resorption exceeds net bone formation. This age-related bone los s can be regarded as the main determinant of hip fracture risk in the elderly. In the concept of senile osteoporosis, a key role has been at tributed to vitamin D deficiency. Lack of vitamin D activity may affec t femoral strength through impaired mineralization as well as through a hyperparathy-roidism-mediated increase in bone resorption. In additi on to vitamin D-related mechanisms, recent evidence has indicated a de cline in the skeletal content of anabolic growth factors - such as ins ulin-like growth factor-I (IGF-I) - in femoral (cortical) bone, sugges ting that skeletal growth factor deficiency may contribute to the age- related bone loss in the proximal femur as well. It is tempting to spe culate that skeletal IGF-I loss might, at least par tially, be account ed for by growth hormone defi ciency. However, critical evidence does not yet support the concept that the decreased activity of the growth hormone-IGF-I-axis alters bone remodeling, and the extent to which ser um concentrations of growth factors are reflective of skeletal activit y remains to be clarified.