For the past three years, NASA scientists have been examining the differences between how male and female astronauts' health is affected by spaceflight. The results are fascinating.

Image credit: NASA/NSBRI

Back in 2011, NASA and the National Space Biomedical Research Institute (NSBRI) — on the recommendation of the National Academy of Sciences — assembled six workgroups to investigate and summarize the current body of knowledge about human and animal spaceflight. The groups focused on cardiovascular, immunological, sensorimotor, musculoskeletal, reproductive and behavioral implications on spaceflight adaptation for men and women. The results have now been published in the latest edition of the Journal of Women's Health.


The study — done in anticipation of longer-duration spaceflights — will inform the health and safety considerations required for astronauts, particularly as they pertain to sex and gender differences.

And yes, the working groups considered both sex and gender. As noted by NASA:


Although in recent years the definitions have become more nuanced in the clinical community, "sex" is defined here as the classification of male or female according to an individual's genetics and "gender" refers to a person's self-representation as male or female based upon social interactions. We know that on Earth, major components of the human body are influenced by sex and gender factors. Taking gravity away from the equation imposes an entirely new element on our understanding of the health implications of sex and gender differences.

The working group listed differences that arise from exposure to natural environments and those instigated by exposure to spaceflight. For example, females suffer less from hearing loss with advancing age (a health effect observed on Earth), and they don't exhibit significant signs of visual impairments after exposure to microgravity (a health effect observed in space). Men, on the other hand, experience deficits in both of these areas. Information like this will help mission planner accommodate the unique needs of male and female astronauts.

Here's a summary of the major findings:


  • Orthostatic Intolerance, or the inability to stand without fainting for protracted periods, is more prevalent upon landing in female astronauts than in their male counterparts. One possible reason for this observed difference in orthostatic intolerance between the sexes is reduced leg vascular compliance, which was demonstrated in bed-rest studies – which is a ground analog for spaceflight.
  • Women have greater loss of blood plasma volume than men during spaceflight, and women's stress response characteristically includes a heart rate increase while men respond with an increase in vascular resistance. Still, these Earth observations require further study in space.
  • The VIIP syndrome (visual impairment / intracranial pressure) manifests with anatomical ocular changes, ranging from mild to clinically significant, with a range of corresponding changes in visual function. Currently 82% of male astronauts vs. 62% of women astronauts (who have flown in space) are affected. However, all clinically significant cases so far have occurred in male astronauts.
  • Changes in function and concentration of key constituents of the immune system related to spaceflight have been reported. However, differences between male and female immune responses have not been observed in space. On the ground, women mount a more potent immune response than men, which makes them more resistant to viral and bacterial infections; once infected, women mount an even more potent response. This response, however, makes women more susceptible to autoimmune diseases. It is not clear if these changes on the ground will occur during longer space missions, or missions that involve planetary exploration (exposure to gravity).
  • Radiation presents a major hazard for space travel. It has been reported that female subjects are more susceptible to radiation-induced cancer than their male counterparts; hence radiation permissible exposure levels are lower for women than men astronauts.
  • Upon transition to microgravity after arriving at the International Space Station (ISS), female astronauts reported a slightly higher incidence of space motion sickness (SMS) compared with men. Conversely, more men experience motion-sickness symptoms upon return to Earth. These data were however not statistically significant, due both to the relatively small sample sizes and small differences in the incidence of SMS reported by the men and women astronauts.
  • Hearing sensitivity, when measured at several frequencies, declines with age much more rapidly in male astronauts than it does in female astronauts. No evidence suggests that the sex-based hearing differences in the astronaut population are related to microgravity exposure.
  • The human musculoskeletal response to gravity unloading is highly variable among individuals and a sex-based difference was not observed.
  • Urinary tract infections in space are more common in women and have been successfully treated with antibiotics.
  • There is no evidence of sex differences in terms of behavioral or psychological responses to spaceflight. Analysis of ISS astronauts' neurobehavioral performance and sleep measures showed no sex or gender differences using the Psychomotor Vigilance Test (PVT) of alertness and Visual Analog Scales of workload, stress, and sleep quality. Since all all astronaut candidates undergo a robust process of psychological screening and selection, the likelihood of an adverse behavioral health condition or psychiatric disorder is greatly diminished.

While much of the data was derived by studying astronauts who spent time aboard the International Space Station, there is an imbalance of data available for men and women, primarily due to fewer women having flown in space. Clearly, that's something that needs to be fixed.



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