The Bodily Effects of Microgravity on Men and Women
In order to become a National Aeronautics and Space Administration (NASA) astronaut, applicants must satisfy a rigorous set of personal requirements and succeed in a strenuous physical fitness test. With an acceptance rate 57 times lower than Stanford University (0.065%), the most selective university in the world, the title of NASA astronaut is sought after by only the most qualified and driven applicants (Ward). At such a high performing level, men and women should be expected to execute the same job, but this is simply not the case. Women are allowed to spend just over half of the time in space as their male counterparts, and are encouraged to take preflight precautions. This restriction exists because of the ways in which microgravity affects men and women differently, specifically with respect to reproductive and sensory health.
One of the biggest differences between men and women is the reproductive system. While this does not affect an astronaut’s ability to perform their duty, it can lead to potentially serious health effects. Women and men create their sex cells, or gammytes, in entirely different ways. All of a woman’s gametes are produced during fetal development; women are born with approximately one million eggs, four hundred will be successfully ovulated during their reproductive life (“Cleveland Clinic”). On the other hand, men are continually producing new sperm. The average man will produce around five-hundred billion sperm cells in a lifetime (“Cleveland Clinic”).
Women and men both experience temporary infertility in and after returning from space due to high levels of ionizing radiation exposed to gonads (Mark). In men, this is not a problem; they will be producing healthy sperm again within a few weeks. Conversely, any damage that occurs to a woman’s reproductive cells is permanent because new eggs are not being produced. Experiments have shown that fetal mice embryos conceived in spaceflight are not viable (Mark). While mice are not always a perfect analog for humans, NASA deems the risk of genetic mutation or permanent female infertility high enough that female astronauts are encouraged to have their eggs cryopreserved before spaceflight (Mahoney). While this can be a burden, the decision of whether or not to have their gametes preserved is left to the individual.
While women are at higher risk for reproductive damage, men tend to suffer higher rates of Visual Impairment Intracranial Pressure syndrome (VIIP). The cause of VIIP is still considered unknown, but is likely caused by the microgravity environment (Mark). The symptoms of VIIP range from headaches to vision loss. While headaches may be a simple nuisance, they can lead to decreased productivity and an increased chance of error. The consequences of vision loss are more severe, and could result in serious equipment malfunction if lost during re-entry or while controlling a space vehicle. VIIP is experienced in 82% of men and 62% of women; NASA is still researching different treatments for the symptom, and currently is unaware of any preventative measures that can be taken (Mark). Even though this condition is not common on Earth, there is a very clear causal relationship between a microgravity environment and VIIP (Mark).
Differences between women and men are important in many areas of science, particularly where health is concerned. The Food and Drug Administration officially recognizes that it is important to include both men and women in clinical trials (“Guidance”). Men and women react to drugs in different ways, and NASA understands that they react to different environments, too. While the imposition of different restrictions may seem to create inequity, it is in the interest of the health of these brave men and women. Just as some medications are dosed differently between the sexes, thousands of hours of research has concluded that space is the same way. Astronauts’ jobs are dangerous enough; NASA does what it can to ensure both equal opportunity and the highest level of safety it can for its astronauts until effective treatments are developed.
Refrences
“Guidance for the Study and Evaluation of Gender Differences in the Clinical Evaluation of Drugs” Accessed March 1, 2020. https://www.fda.gov/media/71107/download.
“Female Reproductive System | Cleveland Clinic.” Accessed March 1, 2020. https://my.clevelandclinic.org/health/articles/9118-female-reproductive-system.
Mahoney, Erin. “Study Investigates How Men and Women Adapt Differently to Spaceflight.” Text. NASA, January 28, 2016. http://www.nasa.gov/content/men-women-spaceflight-adaptation.
Mark, Seralyn. “The Impact of Sex and Gender on Adaptation to Space: Executive Summary.” Accessed March 1, 2020. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4236030/.
Ward, Marguerite. “Meet the 12 Americans Training to Be NASA’s Newest Astronauts.” CNBC, June 14, 2017. https://www.cnbc.com/2017/06/14/meet-the-12-americans-training-to-be-nasas-newest-astronauts.html.