Astronaut Hip Fractures Tied to Long Spaceflights

Astronauts who spend more than three months in space face a higher rate of astronaut hip fractures, occurring at a younger age than expected, according to a study published in Mayo Clinic Proceedings and reported by Phys.org on October 1, 2026. The research, which surveyed US-based astronauts about fractures recorded during annual clinical exams, offers some of the strongest clinical evidence yet that spaceflight-induced bone loss leads to real, lasting fracture consequences. The findings arrive as space agencies plan extended stays on the Moon and eventual missions to Mars, where crews will spend far longer in weightlessness than most International Space Station crews do today.

According to the report, investigators analyzed the survey data with Bayesian probabilistic modeling and found no increase in the overall fracture rate across the cohort. But the rate of astronaut hip fractures rose after spaceflights lasting more than 90 days — exceeding the rate seen before a long-duration mission and among astronauts with no spaceflight exposure. The hip, a load-bearing joint that depends heavily on mechanical stress to maintain density, appears especially vulnerable to prolonged weightlessness.

"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," said Moshe Gertzulin, M.D., of the Endocrinology and Metabolic Bone Disease Service at the Hospital for Special Surgery in New York, a co-author of the accompanying editorial "Bone Loss in Astronauts."

The limits of the evidence

Editorial co-author Matthew T. Drake, M.D., Ph.D., noted that a limitation of spaceflight bone-loss data is accuracy, since astronaut cohort sample sizes are small and spaceflights are rare. The authors emphasize that the study establishes an association between long missions and later astronaut hip fractures — not proof that any given astronaut will suffer one. In a field where the entire population of subjects numbers in the hundreds, each new dataset carries weight precisely because data points are so scarce.

How orbit weakens bones

NASA-funded studies have long shown that astronauts lose hipbone strength of 0.6 to 5.0 percent per month in orbit, according to earlier reporting — monthly losses comparable to what an elderly woman loses in an entire year. Without gravity pulling on the skeleton, bone-building cells slow down while bone-resorbing cells keep working, leaving structures like the hip measurably weaker after long missions. Additional reporting on the study's findings underscores that the problem is cumulative: the longer the mission, the more skeletal resilience erodes, raising the lifetime risk of astronaut hip fractures.

The push for better skeletal surveillance mirrors a broader shift across clinical research toward earlier, more precise detection. Recent examples include an FDA-recognized blood test for scoliosis and new insights into preventing brain metastasis — both cases where catching disease before irreversible damage changes the outcome.

What researchers want to change

The investigators urged expanding NASA's bone surveillance beyond dual-energy X-ray absorptiometry (DEXA) measurements of bone mineral density. NASA has recently begun ordering quantitative computed tomography (CT) scans before and after spaceflight to assess bone structure and determine whether astronauts have fully recovered once back on Earth — a step the authors view as essential, since density alone does not reveal how fragile a bone has become.

The researchers also advocate preventive measures to preserve astronauts' baseline, preflight skeletal health, and call for characterizing which interventions — drugs, exercise, or dietary adjustments — best protect long-term skeletal health. Pinning down the most effective countermeasures is increasingly urgent: exercise equipment on the International Space Station slows bone loss but does not fully prevent it, and future deep-space habitats will need protocols proven over multi-year exposures.

Why it matters

For space agencies, the timing could not be more pointed. NASA's Artemis program aims to establish a sustained human presence on the Moon, and any eventual Mars mission would keep crews in space for well over a year — far past the 90-day threshold where astronaut hip fractures began climbing in this study. Understanding and mitigating that risk is now part of certifying that future explorers can come home with their skeletons intact.

For everyone else, the findings double as a reminder that bone is living tissue shaped by mechanical loading. The same principle — stress keeps skeletons strong — underlies osteoporosis prevention on Earth, where weight-bearing exercise and adequate calcium and vitamin D remain the best-studied defenses against fractures. What happens in orbit, in other words, is an accelerated version of what happens on Earth when bones go unloaded.