Spaceflight May Reduce Fertility in Mice for Generations, Study Finds

Female mice that spent 42 days aboard the International Space Station produced offspring and descendants with lower fertility, smaller litters and changes in reproductive hormones. What the findings mean for human astronauts remains unknown.

A new study suggests that long-duration spaceflight may affect reproductive health across multiple generations of mice. Although the female mice that traveled to the International Space Station (ISS) remained fertile themselves, their offspring and grandchildren showed measurable changes, including fewer litters, smaller litter sizes and lower levels of key reproductive hormones.

The research was published June 30 in the journal Proceedings of the National Academy of Sciences (PNAS).

Space-traveled mice remained fertile, but their descendants changed

In the study, 20 female mice lived aboard the ISS for 42 days before returning to Earth. The mice were able to become pregnant and give birth to live offspring, and their fertility was similar to that of mice kept on Earth.

The pups born to the space-traveled mice were slightly smaller than those in a control group. However, that difference was not statistically significant, meaning it may have occurred by chance.

More pronounced differences appeared in later generations. The muscle strength of the second-generation mice was about 15% lower than that of the control group. Behavioral tests also indicated that female mice in that generation were more susceptible to stress.

The second-generation mice could become pregnant, but they produced fewer and smaller pups than the control mice. Researchers also found lower levels of anti-Müllerian hormone (AMH), a hormone associated with the number of eggs remaining in the ovaries. AMH levels were also lower in the third generation compared with control mice.

“Almost every marker we looked at had some difference,” study co-author Lane Christenson, a professor of cell biology and physiology at the University of Kansas Medical Center, told Live Science.

Why spaceflight could affect reproduction

The researchers suspect that exposure to microgravity may contribute to accelerated aging in reproductive cells. Previous studies of mice and human tissue suggest that reduced gravity can make cells more vulnerable to stress, potentially affecting mitochondria — the structures that produce energy for cells.

Because mitochondrial DNA is passed from mothers to their children, changes in mitochondria could potentially help explain why some effects appeared in later generations. However, the relationship between this proposed mechanism and reduced fertility has not yet been confirmed.

Reproductive hormones may also affect health beyond fertility. Estrogen, for example, supports processes throughout the body, including the maintenance of healthy bones.

What earlier space research found

Few studies have examined the long-term effects of spaceflight on reproduction. A previous NASA twin study compared astronaut Scott Kelly, who spent nearly a year aboard the ISS, with his identical twin brother, Mark Kelly, who remained on Earth. That research helped identify health changes associated with spaceflight but did not fully address reproductive outcomes.

Research published in 2019 also found that male mice exposed to spaceflight were able to produce healthy offspring. The new study was designed in part to address what Christenson described as a gap in research on how spaceflight affects the female reproductive system.

Human astronauts may face different risks

Because the study involved mice, it is not possible to determine whether the same effects would occur in humans. Still, mice are useful models for studying health effects because they are mammals with reproductive systems that share important biological features with humans.

Human menstrual cycles average about 28 days, while female mice have reproductive cycles lasting roughly four to five days. Even so, the researchers noted that the molecular patterns involved in hormonal fluctuations are broadly similar.

The risks could be different during missions beyond low-Earth orbit. The ISS is less exposed to cosmic radiation than deep space, such as the environment astronauts would encounter during a trip to Mars.

In research presented earlier this year, scientists found that radiation levels astronauts might experience during a Mars mission caused a significant reduction in the number of eggs and follicles in mouse ovaries.

Ulrike Ruderer, director of the Center for Occupational and Environmental Health at the University of California, Irvine, was not involved in the study. She said future research should examine additional reproductive markers, including hormone levels, to better understand the long-term effects of deep-space travel.

More research is needed before drawing conclusions

The study does not show that spaceflight causes infertility in humans. Instead, it adds to growing evidence that long-duration space travel may affect reproductive biology in ways that can persist beyond the individuals who experience the journey.

As scientists investigate missions to Mars and the possibility of long-term human habitation beyond Earth, understanding how microgravity and cosmic radiation affect fertility will become increasingly important.

Study: Hong, X., et al. (2026). “Female reproductive dysfunction associated with long-duration spaceflight and its transgenerational effects.” Proceedings of the National Academy of Sciences, 123(27).

This article is for informational purposes only and does not provide medical advice.