The NASA Twins Study
Multi-omicsCardiovascularNeuro-ophthalmicImmune & HematologicNeurological & CognitiveIn-flightPostflight RecoveryLEO long-durationPublicStudentClinicianResearcher
- A year in space changed many measures, including gene expression, telomeres, the microbiome, carotid arteries, eyes and cognition. ◆◆◇◇ Low · F
- Most changes returned to near preflight levels within 6 months. More short telomeres and some disrupted gene expression persisted. ◆◆◇◇ Low · F
- With one twin pair, the findings generate hypotheses. They can't be generalized to all astronauts. ◆◆◆◆ 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.
What was done
One identical twin astronaut was monitored before, during and after a 1-year mission on the International Space Station. His twin brother stayed on Earth as a genetically matched control [1]. NASA brought ten research teams together to study physiological, molecular and cognitive changes [2].
Key findings
Changes seen during or after spaceflight included [1]:
- decreased body mass
- telomere elongation (longer chromosome caps) in flight
- genome instability
- carotid artery distension and increased intima-media thickness
- altered eye structure
- changes in gene activity (transcription), metabolism and DNA methylation in immune and oxidative-stress pathways
- changes in the gut microbiome
- some decline in cognition after flight
What reversed, and what didn’t
Average telomere length, overall gene expression and the microbiome returned to near preflight levels within 6 months after return. But the number of short telomeres increased, and some genes were still disrupted [1].
Why it matters
The study was a first map of how a long mission affects the body from molecules to behavior. Its data now sit alongside newer missions in the Space Omics and Medical Atlas (SOMA) [3]. For example, the immune “spaceflight signature” from Inspiration4 was confirmed in the Twins data [4].
Limitations
- One pair (n = 1). Individual differences can’t be separated from spaceflight effects.
- Results apply to one middle-aged male astronaut on a 1-year ISS mission.
Where to find the data
See Datasets & resources. The SOMA browser includes cross-mission comparisons that use Twins Study data [3].
Evidence profile
- Overall certainty
- ◆◆◇◇ Low (proposed)
- Evidence types
- F · Flight data
- Literature through
- 2026-10-14
Requirements referenced 0
No NASA-STD-3001 requirement maps directly to this page. See the standards quick reference.
References 4
- Garrett-Bakelman FE, et al. The NASA Twins Study: a multidimensional analysis of a year-long human spaceflight. Science. 2019;364(6436):eaau8650. doi:10.1126/science.aau8650 PMID:30975860 Peer-reviewed F
- NASA. NASA Twins Study. www.nasa.gov/humans-in-space/twins-study/ NASA E
- Overbey EG, et al. The Space Omics and Medical Atlas (SOMA) and international astronaut biobank. Nature. 2024;632:1145–1154. doi:10.1038/s41586-024-07639-y PMID:38862028 Peer-reviewed F
- Kim J, et al. Single-cell multi-ome and immune profiles of the Inspiration4 crew reveal conserved, cell-type, and sex-specific responses to spaceflight. Nat Commun. 2024;15:4954. doi:10.1038/s41467-024-49211-2 PMID:38862516 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