When the four-person crew of Axiom Mission 2 launched on a 10-day mission to the International Space Station in May 2023, their schedule was packed with biomedical research aimed at understanding how the human body responds to spaceflight. Now, a new analysis of blood samples from that mission suggests that short-duration spaceflight may briefly accelerate biological aging—while also revealing signs of an intrinsic capacity for recovery once astronauts return to Earth.
Astronaut Bruce McCandless made the first untethered spacewalk as he flew about 300 feet from the shuttle in the first test of the Manned Maneuvering Unit on Feb. 7, 1984. The event pictured here took place a few days later on February 11. (Image credit: NASA)
The study, led by scientists at the Buck Institute for Research on Aging, positions spaceflight as a powerful real-world model for studying the biology of aging and cellular resilience. By examining how extreme environmental stressors reshape molecular markers associated with aging, researchers say orbital missions may offer unique insights into how the human body copes with—and rebounds from—accelerated physiological stress.
Astronauts experience a rare convergence of stressors during spaceflight, including microgravity, elevated ionizing radiation, disrupted circadian rhythms, and social isolation. Together, these factors are difficult to replicate on Earth and provide what researchers describe as a natural testbed for aging biology.
Working with collaborators at Weill Cornell Medicine and King Faisal Specialist Hospital and Research Centre, the Buck Institute team developed a composite metric known as epigenetic age acceleration, or EAA. The approach integrates data from multiple DNA methylation–based “aging clocks” to estimate how biological age changes over time under spaceflight conditions.
Using blood samples collected before launch, during the mission, and after landing, the researchers found that the astronauts’ average epigenetic age increased by 1.91 years by flight day seven. The finding points to a rapid molecular response to the space environment, with aging-associated signatures emerging within days of exposure.
Notably, those changes did not persist. After returning to Earth, biological age estimates declined in all four crew members. Older astronauts returned to their preflight epigenetic age, while younger astronauts showed biological age readings that dipped below their baseline levels.
The results suggest that the aging-related effects of short-term spaceflight are largely reversible and that the human body may possess built-in mechanisms that counteract age-accelerating stress. “These results point to the exciting possibility that humans have intrinsic rejuvenation factors that can counter these age-accelerating stressors,” said senior author David Furman, an associate professor at the Buck Institute and director of its AI and Bioinformatics Core.
To better understand the drivers of these changes, the team applied 32 different DNA methylation aging clocks and analyzed shifts in immune cell populations over the course of the mission. They found that changes in immune cell composition explained a substantial portion of the apparent age acceleration, with regulatory T cells and naïve CD4 T cells showing especially pronounced responses to spaceflight.
Even after adjusting for immune cell redistribution, several aging clocks continued to indicate accelerated aging signatures during flight. This, the authors say, points to epigenetic remodeling that goes beyond simple changes in circulating immune cells, reinforcing the idea that spaceflight triggers deeper, yet reversible, molecular adaptations.
The researchers argue that the expanding cadence of commercial and government space missions now creates an opportunity to test potential geroprotective interventions. By pairing molecular aging clocks with immune system readouts, future missions could be used to evaluate countermeasures aimed at slowing or reversing biological aging in real time.
In parallel with the astronaut study, Furman’s group is modeling aspects of microgravity in the laboratory using organoids derived from heart, brain, and immune cells. The team has developed and patented technology that reproduces elements of microgravity in vitro, an innovation that has been licensed to a spin-off company developing tools for drug discovery and consumer-facing aging interventions.
The findings add to a growing body of evidence linking immune system dynamics, epigenetic regulation, and environmental stress exposure to long-term health and lifespan outcomes. The study, published in the journal Aging Cell, appears under the title “Astronauts as a Human Aging Model: Epigenetic Age Responses to Space Exposure” and is presented as a proof of concept for future space-based aging research.
Coauthors include Christopher Mason, JangKeun Kim, Jeremy Wain Hirschberg, and Eliah G Overbey of Weill Cornell Medicine, along with Bader Shirah of King Faisal Specialist Hospital and Research Centre. The authors disclosed that Furman is a co-founder of Cosmica Biosciences, a company focused on aging-related technologies, while the remaining authors reported no competing interests.
As human spaceflight extends deeper into low Earth orbit and beyond, the study suggests that astronauts may not only be explorers—but also key participants in uncovering how humans age, adapt, and potentially rejuvenate under extreme conditions.
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