Abstract

The weightlessness experienced in space produces alterations in calcium homeostasis. Astronauts exhibited a negative calcium balance due primarily to hypercalciuria. In addition, the bone mineral density of the calcaneus declined by approximately 4 in Skylab crew members after 84 d of orbital flight. The negative calcium balance and loss of calcaneal bone mineral in normal adults subjected to prolonged bed rest was comparable to that oberserved in space. The pathogenesis of bone loss during space flight and bed rest is not well understood. The observed bone loss would be reversible and of no longterm consequence if the only abnormality was an increased remodeling rate. However, altered bone cell activity would probably result in irreversible bone loss with the premature development of senile osteoporosis many years after space flight. The etiology of the bone changes associated with actual and simulated space flight has not been elucidated but may involve mechanical unloading and/or hypersecretion of corticosteroids. Verf.-Referat