October 1, 2026 – New research has found that the rate of hip fractures in astronauts back on Earth was greater in the time period after an astronaut has been in space for more than 90 days than in the time period following shorter spaceflights or in non-astronauts. The findings of the study in Mayo Clinic Proceedings , published by Elsevier, underscore the need for expanded assessment of long-term skeletal health in astronauts.
The National Aeronautics and Space Administration (NASA) is planning multiple missions with durations of longer than six months in space, including commercial low Earth orbit activity, completing Artemis IV's first human mission to the lunar south pole in 2028, and enabling sustainable surface capabilities for the moon in preparation for Mars. Increased human participation and time spent in extraterrestrial exploration could negatively affect the long-term skeletal health of astronauts selected for their physical fitness and optimal health.
Muscle and bone loss due to the microgravity environment of space is a common physiologic phenomenon among astronauts that suggests a risk for fragility due to an adaptive response to disuse.
Jean D. Sibonga, PhD, lead investigator of the study " Increased Rates of Hip Fractures Associated With Longer Spaceflight Durations " at NASA's Johnson Space Center, noted that humans do not feel the effects of bone loss. After returning from space and feeling stable or recovered, they may resume physically demanding activities despite underlying skeletal changes caused by prolonged disuse. A better understanding of bone health after spaceflight could help astronauts, patients, and clinicians assess long-term health concerns, determine appropriate care, and reduce the risk of injury.
Co-author of the accompanying editorial " Bone Loss in Astronauts " Matthew T. Drake, MD, PhD, Endocrinology and Metabolic Bone Disease Service, Hospital for Special Surgery, New York, notes, "While data to date on bone loss associated with space flight are consistent, a major limitation is accuracy, as astronaut cohort sample sizes are small and spaceflights are rare."
To overcome this statistical limitation, investigators surveyed a cohort of US-based astronauts for all fractures reported during annual clinical exams and analyzed these data using Bayesian probabilistic modeling. While they did not find a higher incidence rate for all fractures, the incidence rate for hip fractures in astronauts was increased after a long-duration spaceflight of more than 90 days.
This increased rate occurred at a younger age than would be expected in a non-astronaut terrestrial population, and at a greater hip fracture rate than the rate before a long-duration mission, or with no spaceflight exposure at all.
"Taken together, the finding of hip fracture occurrence at an age earlier than expected after long-duration spaceflight is clinical evidence that spaceflight-induced bone loss can lead to real long-term fracture consequences, which should be addressed accordingly," says Moshe Gertzulin, MD, Endocrinology and Metabolic Bone Disease Service, Hospital for Special Surgery, New York, co-author of the accompanying editorial.
Dr. Sibonga emphasized the need to expand NASA's current bone surveillance program beyond dual-energy X-ray absorptiometry measurements of bone mineral density to better evaluate astronauts' long-term fracture risk. NASA has recently begun ordering quantitative computed tomography scans before and after spaceflight, which can provide more detailed information about different areas of the bone and whether astronauts have fully recovered. Without that insight, astronauts could risk placing too much strain on bones that have not yet regained their preflight condition.
To mitigate these risks, the investigators advocate for prophylactic countermeasures that would preserve the baseline, pre-flight skeletal health of the astronaut. A fuller characterization of spaceflight-induced changes to bone mass, density, structure, and microarchitecture will determine which interventions—whether drugs, exercise, or dietary adjustments—are most beneficial for long-term skeletal health in astronauts.
