Bone loss & fracture
Also: Bone Fracture risk
Gravity FieldsMusculoskeletalIn-flightPostflight RecoveryLifetime SurveillanceLEO long-durationLunar surfaceMars transit & surfacePublicClinicianResearcher
- Resistance exercise (ARED), with or without bisphosphonates, greatly reduces bone loss during ISS missions. ◆◆◆◇ Moderate · F
- Recovery after flight can be incomplete. A year later, 9 of 17 astronauts had not regained tibia density. ◆◆◆◇ Moderate · F
- NASA has no plans for new research solicitations on this risk. ◆◆◆◆ High · E
Proposed certainty (◆ High → ◇ Very low) and evidence-type tags: F flight · A analog · M model/animal · C computational · E expert/operational/standards. AI-proposed, pending reviewer confirmation. How to read the grades.
NASA risk title (verbatim)
Risk of Bone Fracture due to Spaceflight-induced Changes to Bone
NASA short title: Bone Fracture · HRP element: Human Health Countermeasures (HHC) · Status: Active [current research ongoing] [1]
What it is
Without the normal load of gravity, bone breaks down faster than it rebuilds. NASA’s risk is a fracture, either during a mission (when a load exceeds bone strength) or later in life (from fragile bones) [1].
Current evidence
- There are extensive before-and-after bone density (DXA) measurements for ISS astronauts. Exercise on the Advanced Resistive Exercise Device (ARED) and treadmill six days a week has minimized postflight density losses [1].
- Density alone isn’t enough to judge fracture risk; bone quality matters too [1].
- In 7 ISS astronauts, weekly alendronate plus exercise reduced the expected decline in almost all bone measures. ARED alone reduced bone loss compared with an older resistance device [4].
- Recovery can be incomplete. A year after flight, tibia strength and density in 17 astronauts were still 0.9–2.1% below preflight, and 9 of 17 had not fully recovered tibia density. The authors compared this to a decade or more of age-related bone loss on Earth [5].
- Bone breakdown raises urinary calcium, which links bone loss to kidney stone risk [6].
NASA’s risk posture
NASA scores each risk for each design reference mission (DRM) as likelihood × consequence (LxC). Both run from 1 (lowest) to 5 (highest) on the HSRB’s 5×5 matrix [1][3]. Each score comes with a disposition, such as “Accepted”, “Requires Characterization” or “Requires Mitigation”. These ratings were last approved by NASA’s Human System Risk Board (HSRB) in 5/2022 [1].
| Mission | Duration | In-mission (operations) | Long-term health |
|---|---|---|---|
| LEO | Short (under 30 d) | 1x2 · Accepted | 1x1 · Accepted |
| LEO | Long (30 d–1 yr) | 1x2 · Accepted | 2x2 · Requires Characterization |
| Lunar orbit | Short | 1x2 · Accepted | 1x1 · Accepted |
| Lunar orbit | Long | 2x2 · Requires Characterization | 4x2 · Requires Characterization |
| Lunar orbit + surface | Short | 2x3 · Accepted | 1x1 · Accepted |
| Lunar orbit + surface | Long | 3x3 · Requires Characterization | 4x2 · Requires Characterization |
| Mars preparatory | Under 1 yr | 2x2 · Requires Characterization | 4x2 · Requires Characterization |
| Mars planetary | 730–1,224 d | 4x4 · Requires Characterization | 5x2 · Requires Characterization |
Copied from the Human Research Roadmap on 2026-10-14. Ratings change. Check the live record before citing.
Open knowledge gaps
NASA lists 6 knowledge gaps for this risk, 6 of them open as of 2026-10-14 [1]. Each gap ID links to its page on the Human Research Roadmap (HRR).
Show NASA’s gap list (verbatim)
| Gap | NASA gap statement | Status |
|---|---|---|
| Bone-101 | Characterize skeletal changes on bone mass (Bone Density) and bone structure (Bone Quality) of astronauts. | Open |
| Bone-102 | Characterize bone turnover and other biomolecular markers of skeletal health. | Open |
| Bone-201 | Identify/develop/apply tools (e.g., computational modeling or alternative) to inform the estimation bone strength and probability of overloading bones and fracture assessment. | Open |
| Bone-301 | Identify, develop, and implement monitoring tools for bone health during spaceflight. | Open |
| Bone-401 | Identify and test preventative and mitigating countermeasures for changes induced by spaceflight. | Open |
| Bone-402 | Validate countermeasures for maintaining preflight bone standard. | Open |
See also Open questions.
Active countermeasure research
- Research status. NASA states that HRP currently has no plans to solicit or pursue new research projects on this risk, although some activities are ongoing [1].
- Remaining gaps. These cover bone density and quality, tools to estimate bone strength and fracture risk, in-flight bone monitoring, and testing and validating countermeasures (gaps Bone-101 to Bone-402) [1].
Project-level detail, including status, investigators and results, is in the NASA Task Book and on each HRR gap page.
Clinical articles
For practical, clinic-facing guidance, see:
Evidence profile
- Overall certainty
- ◆◆◆◇ Moderate (proposed)
- Evidence types
- F · Flight dataE · Expert / operational / standards
- Literature through
- 2026-10-14
- NASA source
- Human Research Roadmap risk page (last published 05/13/25; read 2026-10-14)
Requirements referenced 4
| Requirement | Title | Plain-language meaning |
|---|---|---|
| [V1 4026] | Bone Mineral Density Testing | DXA BMD reported as T-scores referenced to sex- and race/ethnicity-matched young adults. |
| [V1 4027] | In-Mission Bone Mineral Density Maintenance | Countermeasures must keep total hip and lumbar spine BMD at ≥95% and femoral neck ≥90% of preflight. |
| [V1 4028] | Post-Mission Bone Mineral Density Recovery | Bone is tracked after flight until return to preflight levels. |
| [V2 7038] | Physiological Countermeasures Capability | Vehicles must provide countermeasure capability (e.g., exercise hardware) to meet crew health standards. |
IDs as published in NASA-STD-3001 Vol. 1 Rev C (2023-09-15) and NASA-STD-3001 Vol. 2 Rev F (2026-07-14). NASA-STD-3001 binds NASA programs; it is not a regulation for commercial flights. Paraphrased. Standards quick reference.
References 6
- NASA Human Research Roadmap. Risk record: “Risk of Bone Fracture due to Spaceflight-induced Changes to Bone”. Accessed 2026-10-14. humanresearchroadmap.nasa.gov/Risks/?i=77 NASA E
- NASA Human Research Program. Evidence report for the Bone Fracture risk (approved July 18, 2024). humanresearchroadmap.nasa.gov/evidence/reports/Bone%20Fractu… NASA E
- Antonsen EL, et al. Updates to the NASA human system risk management process for space exploration. NPJ Microgravity. 2023;9:72. doi:10.1038/s41526-023-00305-z PMID:37679359 Peer-reviewed E
- LeBlanc A, et al. Bisphosphonates as a supplement to exercise to protect bone during long-duration spaceflight. Osteoporos Int. 2013;24(7):2105–2114. doi:10.1007/s00198-012-2243-z PMID:23334732 Peer-reviewed F
- Gabel L, et al. Incomplete recovery of bone strength and trabecular microarchitecture at the distal tibia 1 year after return from long duration spaceflight. Sci Rep. 2022;12:9446. doi:10.1038/s41598-022-13461-1 PMID:35773442 Peer-reviewed F
- Smith SM, et al. Bone metabolism and renal stone risk during International Space Station missions. Bone. 2015;81:712–720. doi:10.1016/j.bone.2015.10.002 PMID:26456109 Peer-reviewed F
Machine-checked on 2026-10-14: each URL resolved, each DOI's title/journal/year matched via Crossref, and claims were checked against the source text (abstract or full NASA page). Human verification against full text is still required before review. NASA documents are U.S. Government works (public domain) and are summarized with attribution; journal articles are summarized, not reproduced.
Article info
- Authors
- Pending (AI-assisted draft)
- Reviewer
- Pending review
- Last reviewed
- Pending review
- Literature through
- 2026-10-14
- AI-assisted
- Yes (disclosed)
- COI
- Pending
- License
- CC BY-SA 4.0
- Use
- Educational only · Disclaimer
- Cite this version
- Pending first edition