Objective: Adults with GH deficiency (GHD) commonly have subnormal bone mineral density (BMD), and have been reported to have an increased risk of fractures. It has been suggested that GH replacement therapy may have beneficial effects on bone in such patients. The aim of this study was to investigate the effects of long-term GH replacement therapy on bone metabolism, BMD and bone elasticity in adults with GHD.
Design: At the start of the study, 20 adults with GHD were randomized to receive either GH, 0.25 IU/kg/week (the 'GH group') or placebo (the 'placebo group'). After 6 months, patients in the placebo group were switched to GH therapy, and all patients received GH for a further 42 months.
Patients: Of the 20 patients included in the study, 11 were male and nine were female. Mean age at the start of the study was 42.5 +/- 10.1 years. All patients had been GH-deficient for at least 2 years before the start of the study.
Measurements: Rates of bone resorption and formation were assessed by measuring serum levels of type I collagen carboxyterminal cross-linked telopeptide (ICTP) and carboxyterminal propeptide of type I procollagen (PICP), respectively. BMD was measured at the lumbar spine by dual-photon absorptiometry (DPA) and at the non-dominant forearm by single-photon absorptiometry (SPA). Bone elasticity was assessed by measuring apparent phalangeal ultrasound transmission velocity (APU).
Results: The main results in the GH group were as follows. The rate of bone resorption increased significantly during the first 6 months of treatment and remained significantly elevated above its baseline level thereafter. The rate of bone formation also rose during the first 6 months of treatment and remained elevated thereafter, but was significantly higher than at baseline only after 24 months of treatment. At both sites measured, BMD was subnormal at baseline, decreased during the first 6 months of treatment, and increased progressively for the rest of the study, eventually rising well above its baseline level. Bone elasticity decreased during the first 6 months of treatment, but had returned to its baseline level after 24 months.
Conclusions: Our results support previous findings that BMD is subnormal in adults with GHD, that GH replacement therapy can stimulate bone turnover in such adults and that, in the long term, such stimulation results in a significant increase in BMD. In addition they show, for the first time, that BMD may continue to rise even after GH replacement therapy has been administered for 4 years, and indicate that bone elasticity is not adversely affected by long-term GH therapy.