Insulin-like growth factors I and II: aging and bone density in women

Serum concentrations of insulin-like growth factors (IGF) were measured by RIA in 57 normal women, ages 30 - 90 yr, and in 29 untreated women with postmenopausal osteoporosis and vertebral compression fractures, ages 55 - 75 yr. These values were correlated with bone mineral density (BMD) of the distal and midradius assessed by single photon absorptiometry and of the lumbar spine assessed by dual photon absorptiometry as well as serum and urinary calcium, phosphorus, creatinine, alkaline phosphatase, immunoreactive PTH, urinary hydroxyproline, and creatinine clearance. Serum IGF-I levels declined markedly with age (r = -0.47, P less than 0.001). Serum IGF-II levels decreased only slightly with age, and this decrease was not statistically significant. Although BMD at all three scanning sites also declined significantly with age, neither serum IGF-I nor II concentrations correlated with BMD when age was held constant. In women with postmenopausal osteoporosis, serum IGF-I and II did not differ from the concentrations in normal women of similar age and did not correlate with BMD. In neither group was a correlation between serum IGF-I or II and serum or urinary proteins or cations found. Thus, there was no evidence that impaired synthesis of IGF-I and II contributes to pathogenesis of the syndrome of Type I (postmenopausal) osteoporosis, which is characterized by accelerated loss of trabecular bone and vertebral compression fractures. The possibility remains, however, that decreasing concentrations of serum IGF-I play a role in the more gradual loss of bone with aging (Type II osteoporosis) in which impared bone formation at the cellular level has been demonstrated.