Rocket science: what spaceflight can tell us about skeletal health on Earth

In BJSM , Gabel and colleagues in their paper ‘Pre-flight Exercise and Bone Metabolism Predict Unloading-Induced Bone Loss due to Spaceflight’ study skeletal health in a unique population of ‘occupational athletes’: astronauts.1 Astronauts frequently experience cardiovascular deconditioning, immune suppression, balance disorders, strength deficits and bone loss as a result of space travel.2 After more than 50 years of space missions, various contributors to bone loss in astronauts have been postulated—microgravity, radiation, stress, metabolic disruption and altered calcium homeostasis all likely play a role.3 Using high-resolution three-dimensional imaging (HR-pQCT), Gabel et al report declines in bone mineral density (BMD), bone microstructure and strength at the distal tibia, although minimal changes at the distal radius.1 Their findings are broadly similar to prior reports, revealing an average rate of bone decline nearly 10-fold higher than that seen in postmenopausal women, although with remarkable interindividual variability seen in these astronauts.4 Notably, their analyses bring several new insights to our understanding of unloading-induced bone loss. For spaceflight of 3.5–7 months, mission time predicted tibial BMD loss linearly, with accelerated trabecular bone loss in longer flights.1 …