Spaceflight Accelerates Ageing in Human Stem Cells, New Study Finds

A team of University of California researchers has found that time in low-Earth orbit accelerates ageing in human stem cells, reducing their ability to generate healthy new cells and increasing markers of cellular damage.

Scientists sent stem cells to the International Space Station on four supply missions lasting between 32 and 45 days and compared them with identical cells kept on Earth. Analysis after return showed the space-flown cells suffered greater DNA damage, shortened telomeres — the protective caps at the ends of chromosomes associated with cellular ageing — and a diminished capacity for normal regenerative function.

"Space is the ultimate stress test for the human body," said Professor Catriona Jamieson, director of the Sanford Stem Cell Institute at the University of California, San Diego. Researchers said the findings provide a cellular-level explanation for some health risks already observed in astronauts and highlight the need to understand how microgravity and space radiation affect the body's repair systems.

Astronauts are known to face a range of physiological problems during and after spaceflight, including muscle atrophy, bone loss and elevated cancer risk linked to space radiation. The new study focused on stem cells because they underpin the body's ability to repair tissue and maintain health over a lifetime. Deterioration in stem cell function could therefore have wide-ranging implications for long-duration missions.

The study measured multiple biomarkers of cellular health. Telomere shortening is commonly interpreted as a sign of accelerated cellular ageing. Increased DNA damage can impair a cell's genetic integrity and function, while a reduced capacity to generate healthy progeny indicates compromised regenerative potential. Together, the changes observed in the flight samples suggest that the combined stressors of microgravity and elevated radiation in low-Earth orbit can alter fundamental properties of human stem cells even over periods of a few weeks.

Researchers cautioned that the missions studied were relatively short and that translating cellular changes into clinical outcomes for astronauts requires further work. The experiments took advantage of repeated supply flights to the space station to create a controlled comparison between flown and ground-control samples, but the team called for additional studies with longer durations and different cell types to map the trajectory of damage and recovery.

The findings are relevant to space agencies and private companies planning crewed missions beyond low-Earth orbit, including expeditions to the Moon and Mars that would expose astronauts to prolonged microgravity and higher cumulative radiation doses. Understanding how stem cells respond to space conditions could inform medical monitoring, selection and development of countermeasures such as radiation shielding, pharmaceutical interventions or in-flight therapies designed to protect tissue repair mechanisms.

Beyond mission planning, the investigators noted that spaceflight experiments can illuminate how extreme environments influence basic biology. Treating space as a natural laboratory may reveal pathways that govern ageing and repair on Earth, with potential applications for regenerative medicine. The authors urged continued international research cooperation to expand the dataset and to test mitigation strategies aimed at preserving stem cell function during and after space travel.

The study adds to a growing body of research documenting how the space environment affects human physiology at multiple scales, from whole-body changes to molecular and cellular alterations. Scientists said the new cellular evidence reinforces the importance of comprehensive health risk assessment as human spaceflight ventures farther from Earth and for longer durations.