A first-of-its-kind research project finds that physiological changes begin to occur in astronauts' bodies at the very beginning of their stay in space, also suggesting that women might be more suited for space travel than men.

“Certainly some of the tests we had out there were the most trying, and it’s rather difficult to pick one. Because if you figure how many openings there are in the human body and how far you can go in any one of them, you can answer which one would be the toughest for you," remarked John Glenn, the first American to orbit the Earth, reflecting on the rigorous medical evaluations undergone by NASA's first astronauts. At that time, the physical challenges of space were largely unknown and thus the medical teams conducted every possible test in order to select the healthiest pilots. Over the years, significant knowledge has accumulated regarding the medical effects of spaceflight on the human body, yet the subjects have typically been professional astronauts—remarkably fit individuals selected after very rigorous medical screenings.

Over the years, a few tourists who are neither professional astronauts nor have undergone the same rigorous medical screenings have also traveled to space, although the medical data they have provided remains relatively limited. In recent years, a new category, known as "private astronauts", has emerged. In recent years, a new category known as "private astronauts" has emerged. These individuals are not trained astronauts and do not meet the health requirements of traditional astronauts but embark on short space missions, some involving work in space such as scientific experiments. The first fully private mission to orbit the Earth was Inspiration 4, during which four individuals flew aboard SpaceX's Dragon spacecraft for a three-day journey around the planet. Subsequently, several private astronaut missions, including Israeli Eytan Stibbe aboard the AX-1 mission by Axiom Space, have visited the International Space Station.

A series of studies published in recent days focused on examining bodily changes during spaceflight, analyzing medical data from the four crew members of the Inspiration 4 mission. Comparisons were made with data from numerous professional astronauts, including the renowned American study on twin astronauts Scott and Mark Kelly, which tracked their metrics while one was aboard the space station and the other on Earth. Researchers have also established a database of biological data aimed to serve as the information base for understanding the impact of space flight on "ordinary" people -  individuals with a medical history far removed from the near-perfect health of professional astronauts. “This is the beginning of precision medicine for spaceflight,” said geneticist Christopher Mason from Weill Cornell Medicine,  the medical college of Cornell University in New York, one of the leaders of the project who himself co-authored several of the 44 mentioned reports. “Let’s bring the full armamentarium of modern molecular biologist tools to bear for these crews who are regular people.”

Most data so far comes from professional astronauts who underwent rigorous medical screenings. Astronaut André Kuipers taking a blood sample from Dan Burbank on the International Space Station. | Photo: NASA

Rapid Changes

The Inspiration 4 mission team included Jared Isaacman, 48 at the time, a billionaire who bought the mission from SpaceX; Sian Proctor, a 51-year-old geologist; Christopher Sembroski, 42, a former U.S. Air Force missile program engineer; and Hayley Arceneaux, 29, the youngest American to orbit Earth and likely the first cancer survivor in space, with a metal prosthesis replacing a bone in her leg. This diverse crew marked a departure from typical space missions in terms of age range, medical history, and even gender balance. During the three-day mission, they collected blood, urine, and saliva samples, performed ultrasound scans and cognitive tests on themselves, and wore sensors monitoring heart rate, blood pressure, and other metrics.

Researchers analyzed these samples and measurements, uncovering surprising findings that indicated physiological changes in the crew immediately upon reaching Earth orbit. Notably, changes in immune cell function of the crew members were observed, including alterations in the expression levels of no fewer than 18 cytokines - substances secreted during an inflammatory response. Additionally, the researchers identified specific changes in gene expression, changes in blood protein levels, potentially indicating a decline in the function of the blood-brain barrier (BBB) - the system that prevent foreign substances from entering the brain, microbiome composition changes, and elongation of telomeres - structures found at the ends of chromosomes, the shortening of which is associated with cellular aging. On the other hand, the researchers did not detect an increase in the amount of mitochondrial DNA in blood tests among the Inspiration 4 crew, contrasting findings from longer space missions. However, the researchers noted that about 95% of the changes reverted shortly after the crew's return to Earth, with only some residual effects detectable in tests conducted three months after the mission.

The research on the Inspiration 4 crew has several limitations, notably its small sample size of only four subjects. Validating these findings will necessitate follow-up studies involving private astronauts, other space tourists, and professional astronauts. Another drawback is that most assessments rely on biomarkers: changes in the levels of proteins and other substances in the blood. While biomarkers are essential for research, alterations in protein levels or gene activity may not always indicate a clinical or significant health/medical outcome. These changes could signify the onset of processes that may lead to clinical changes; for instance, it is well-documented that prolonged exposure to microgravity often results in substantial physiological changes, such as loss of bone and muscle mass. "Collecting astronauts’ medical data in a consistent way via the SOMA biobank will help researchers understand more about these changes and potentially develop ways to mitigate them," said Mason.

Intriguing findings, but further extensive research is required in order to understand their significance. The Inspiration 4 mission team floating inside the Dragon spacecraft. | Photo: Inspiration 4 crew

Women Are from Mars

One of the intriguing findings from the aforementioned collection of studies is a series of differences in the physiological responses of men and women to spaceflight. Researchers observed that many changes in gene expression and protein levels appeared more pronounced in men. However, these conclusions are based primarily on the limited sample size of the Inspiration 4 mission, and there have been few comparative studies on the physiological differences between men and women in spaceflight. "The aggregate data thus far indicates that the gene regulatory and immune response to spaceflight is more sensitive in males," the researchers note in their paper. “More studies will be needed to confirm these trends, but such results can have implications for recovery times and possibly crew selection (e.g., more females) for high-altitude, lunar, and deep space missions.”

Are women better suited for spaceflight than men? Hayley Arceneaux (right) and Sian Proctor during the Inspiration 4 mission | Photo: Inspiration4 crew

Even if confirmed, these findings do not necessarily, these findings do not necessarily imply medical differences that could affect women's versus men's performance in space. Nevertheless, this did not deter Mason and his colleagues from quickly suggesting that women might exhibit greater resilience than men to the physiological challenges of space missions, and even speculating on why this might be the case. "Being able to tolerate large changes in physiology and fluid dynamics may be great for being able to manage pregnancy but also manage the stress of spaceflight at a physiological level," Mason remarked to The Guardian.

However, if we discover that women might indeed be better suited physiologically for spaceflight than men, this would be a fitting closure to the legacy of American physician Randy Lovelace. In the late 1950s, he led NASA's medical screenings efforts for astronauts and advocated that women could be as, if not more, suitable for spaceflight due in part to their generally lower weight and oxygen consumption compared to men. Lovelace initiated a program to recruit women for the U.S. space program, though it faced eventual setbacks due to political pressures. It took over two decades for the first American woman to fly to space and an ongoing struggle for gender equality in space to this day. Perhaps in time, science will settle this argument.


Translated with the assistance of ChatGTP. Revised, expanded and edited by the staff of the Davidson Institute of Science Education