Bone Health in Space Flight: Incomplete Bone Mineral Density Convalescence at 1 Year Postmission Without Increased Fracture Risk.

Abstract

Understanding the impact of space flight on orthopaedic health is crucial for optimization of astronaut health, space flight safety, and chance of mission success. This study sought to assess the rate and degree of bone mineral density (BMD) recovery across various anatomic regions on return to Earth, and further how the length of space flight and astronaut age affect BMD recovery. A retrospective cohort study was performed to quantify the changes in BMD and fracture risk after return to Earth. The Lifetime Surveillance of Astronaut Health epidemiology database at National Aeronautics and Space Administration provided preflight and postflight dual-energy radiograph absorptiometry data and Fracture Risk Assessment Tool scores for 94 astronauts. BMD loss and rate of recovery post-space flight was recorded and analyzed. Subanalyses were performed assessing effect of astronaut age and mission duration on BMD recovery and fracture risk. In the hip and the spine, losses in BMD occurred that do not recover to preflight BMD levels by 1 year postflight. Astronauts who spent greater than 6 months in space flight recovered slower and more incompletely at the spine (P = 0.011), hip (P = 0.018), and femur (P = 0.049) compared with those who spent less than 6 months in space flight. No notable difference was observed in the risk of 10-year osteoporotic hip fracture based on duration of space flight or astronaut age. Increasing time in space flight leads to larger losses in BMD and slower BMD rate of return. At 1 year postflight, preflight BMD levels at the hip and spine are only achieved by 34.0% and 46.8% of astronauts, respectively.