A recent study published in the journal PNAS on June 30 reveals that the offspring of mice who lived on the International Space Station (ISS) are more vulnerable to stress and have reduced reproductive abilities. The research involved 20 female mice who spent 42 days aboard the ISS. While the mice themselves had similar fertility levels to those living on Earth, their offspring and even their grandchildren showed notable differences, including smaller litters, fewer litters overall, and lower levels of key reproductive hormones. According to the study's co-author, Lane Christenson, a professor of cell biology and physiology at the University of Kansas Medical Center, the offspring of the spacefaring mice had about 15% less muscle strength than the control group's offspring. Behavioral experiments also showed that female offspring from the space mice were more prone to stress compared to the control group's females. These findings suggest that the effects of space travel may extend beyond the individuals who experience it, potentially impacting future generations. The second generation of mice, born to the spacefaring mothers, could still get pregnant, but they had fewer litters and smaller litters compared to the control group. The offspring also had lower levels of anti-müllerian hormone (AMH), a hormone that reflects the number of eggs a female has. This trend continued into the third generation, which also showed lower AMH levels compared to the control groups. Christenson theorizes that these effects might be due to an "acceleration of aging" caused by the mice's exposure to microgravity. This could be linked to dysfunction in mitochondria, the energy-producing parts of cells that contain DNA passed only from mother to child. However, this mechanism still needs to be confirmed through further research. The study underscores the need for more research on how long-term space travel affects the reproductive system, especially for human astronauts and their families. While the research was conducted on mice, they are considered good models for studying the health impacts of space travel due to their similar reproductive systems to humans. Previous studies, such as NASA's Twins Study, suggested that short-term spaceflight has only modest effects on human health, but long-term impacts—particularly on reproduction—remain largely unexplored. Dr. Ulrike Luderer, director of the Center for Occupational and Environmental Health at the University of California, Irvine, pointed out that the ISS is exposed to less cosmic radiation than deeper space, such as a journey to Mars. She suggested that the health risks of deep space travel could be even more severe. Earlier this year, Luderer's research found that exposing mice to radiation levels similar to those on a Mars mission led to a significant decrease in ovarian eggs and follicles, further highlighting the potential risks of long-duration space travel.