Mouse Study Suggests Spaceflight Risks to Reproductive Health Across Generations

Research published June 30 in the journal Proceedings of the National Academy of Sciences (PNAS) suggests that time spent in space by female mice may negatively impact the reproductive health of their offspring and grandchildren. While the mice themselves retained the ability to conceive and deliver live young, their descendants exhibited reduced fertility markers and other physiological changes.

The study focused on 20 female mice that resided aboard the International Space Station (ISS) for 42 days. Upon returning to Earth, these mice produced litters that were only slightly smaller than those of Earth-bound control groups—a difference researchers noted was not statistically significant.

However, the subsequent generations displayed more pronounced deficits. The second generation of mice, known as the offspring of the spacefaring females, demonstrated approximately 15% less muscle strength and higher stress levels in female subjects during behavioral tests. Furthermore, second-generation females produced fewer litters with significantly smaller average sizes compared to controls.

Dr. Lane Christenson, a professor of cell biology and physiology at the University of Kansas Medical Center and co-author of the study, highlighted the breadth of these observations. “Just about every marker we looked at had some differences,” Christenson told Live Science. “The offspring of those that came back from space were altered in their behavior, their muscle, their ability to reproduce further.”

Testing revealed lower levels of anti-Müllerian hormone (AMH) in both the second and third generations of mice descended from spaceflight participants. AMH levels are indicative of overall egg count, with lower concentrations correlating to diminished ovarian reserve. Christenson theorizes that this multi-generational decline may stem from an “acceleration of aging” induced by microgravity. Previous investigations into both mouse models and human tissue have suggested that the absence of gravitational force can increase cellular vulnerability to stress, potentially leading to mitochondrial dysfunction. Mitochondria contain their own DNA, which is inherited exclusively from the mother.

While the findings raise questions about the long-term viability of human reproduction during extended space missions, experts caution against direct extrapolation. Mice are commonly utilized as biological models due to their mammalian similarities to humans, particularly regarding reproductive systems and hormonal fluctuations. Christenson noted that although the mouse estrous cycle lasts only four to five days compared to the human 28-day menstrual cycle, the underlying molecular mechanisms are remarkably similar.

The study addresses a significant gap in space medicine research. Earlier investigations, such as the NASA Twins Study comparing astronaut Scott Kelly’s year-long ISS stay to his Earth-bound twin brother Mark, indicated that short-term spaceflight has modest health effects on humans. Conversely, a 2019 study involving male mice on the ISS found no impairment in their ability to father healthy offspring. Christenson explained that the current research was designed specifically to examine the female reproductive system, noting that hormones like estrogen regulate not only reproduction but also bone maintenance and other organ systems.

Dr. Ulrike Luderer, director of the Center for Occupational and Environmental Health at the University of California, Irvine, who was not involved in the study, commented that the research contributes to a growing body of literature on space travel’s reproductive effects. She emphasized that the ISS environment offers less cosmic radiation exposure than deep space, suggesting that journeys to destinations like Mars could pose even greater risks. Luderer referenced her own recent findings, which demonstrated that radiation levels similar to those experienced on a Mars transit caused a significant decrease in ovarian egg and follicle counts in mice.

The authors conclude that further investigation is essential to understand the long-term consequences of spaceflight on human reproductive health, particularly as humanity moves toward potential colonization of other planets.