Indian-American scientist Brinda K. Rana was one of the 10 principal investigators in NASA's landmark Twin Study, which evaluated identical twin astronauts Scott and Mark Kelly after Scott spent a year aboard the International Space Station (ISS).
In an exclusive interview with THE WEEK, Rana discusses the profound physiological changes astronauts undergo in space—and the remarkable contributions they make to humanity.
Q: Can you describe the most significant physiological and molecular changes you observed in Scott Kelly during his year-long mission aboard the ISS? Also, how long did you prepare for this study? Since he stayed in space for a year, I imagine your preparation must have started well in advance.
A: Absolutely. Let me start with the study itself and our preparation timeline.
Scott Kelly launched in March 2015, but our preparations began as early as 2013. We had to develop and coordinate all the research protocols well ahead of time. There were 10 of us serving as principal investigators on the NASA Twins Study, and I was one of them. Most of us had never met before, so we had to collaborate closely to align our protocols and figure out how to share the biological samples collected in space.
On Earth, we’re used to having ample volumes—say, 10 cc of blood—for our research. However in space, blood volume is reduced, and the total available sample is very limited. So we had to adapt our protocols to work with far smaller volumes—sometimes just one sample shared across multiple research teams. That required extensive planning and coordination, and it was a major part of our preparation.
Q: And what about the physiological changes observed in Scott Kelly?
A: Physiological adaptations to space have been known to NASA for some time. There are acute and long-term effects. One of the most immediate changes in microgravity is fluid shift. On Earth, gravity pulls fluids toward our feet, and our bodies have evolved to counteract that. In space, gravity is absent, but the body continues trying to pump fluids upward—without any gravitational pull to bring them back down. This leads to fluid accumulation in the upper body, causing puffy faces, headaches, and in some cases, vision problems.
Q: Since this was a twin study, you were comparing Scott with his brother Mark, who remained on Earth?
A: Yes, exactly. This was the first integrated study looking at molecular and cellular adaptations alongside known physiological changes. That was the novel aspect.
We examined changes in proteins, RNA, and DNA to track gene expression and other biological markers. One of the most striking findings was a shift in gene expression patterns in Scott compared to his twin Mark. While these changes were significant, perhaps the most remarkable outcome of the study was the demonstration of the body’s resilience.
Despite acute and long-term changes observed in Scott during his time in space, many of these changes returned to baseline within six months of his return to Earth. Those changes, especially in gene expression, went back to the baseline gene expression. So that shows how resilient and adapted the body is to different stressors in the environment.
Q: When you talk about gene expression, I can’t help but think about the radiation astronauts are exposed to in space. Can exposure to such radiation increase the risk of cancer or cause genetic mutations? Have you observed anything along those lines?
A: That’s a very valid concern. Yes, astronauts are exposed to cosmic rays and solar particles while in space. Currently, those aboard the International Space Station (ISS) are still within Earth's orbit, which offers some protection, thanks to Earth's magnetic field and the shielding of the ISS itself. However, the bigger concern is with deep space missions—like those to Mars—where astronauts will leave Earth’s protective bubble and be exposed to much higher levels of radiation.
In those situations, the risk of DNA damage increases significantly, which can potentially lead to cancer or other long-term health issues. Radiation exposure is one of the major areas of study as we plan for extended missions beyond low Earth orbit.
Q: So in a way, even astronauts currently on the ISS are making a personal sacrifice for the benefit of humanity, right?
A: Absolutely. Every astronaut is making a tremendous contribution. They are not only the subjects of physiological and medical studies themselves, but they’re also functioning as scientists in orbit. The ISS is essentially a massive laboratory. Hundreds of experiments are running at any given time—ranging from human biology to plant growth, materials science, and engineering tests. So while they’re participating in studies about their health and adaptation to space, they’re also conducting research that will shape the future of human spaceflight and benefit life on Earth. It’s an incredible act of dedication.
Q: We know that many astronauts experience symptoms like headaches, edema, and decreased blood volume. But not everyone is affected in the same way—some seem to adapt better than others. Why is that?
A: That’s a great question. You're right—while many astronauts show common physiological changes, such as fluid shifts and vision problems, not all of them are affected in the same way. For example, some astronauts return with no significant changes to their eyes, while others, like Scott Kelly, experience major structural changes.
One area of active research at NASA focuses on understanding why that happens. A NASA investigator, Dr Scott Smith, is doing important work in this space—looking into whether genetic differences between astronauts might explain the variability in response. Some astronauts may have specific genes or genetic variants that make them more resilient to vascular stress, which could reduce their susceptibility to issues like vision problems.
Q: In his book, Scott Kelly notes that women may be more physiologically adaptable in space and even suggests NASA should consider sending an all-women crew to Mars. Is there scientific evidence supporting this idea? Are women better adapted to space conditions in some ways?
A: That’s an intriguing point, and it’s something researchers are beginning to study more deeply. One issue we’ve observed is orthostatic intolerance, which occurs when astronauts return to Earth and have difficulty standing because of sudden changes in blood flow due to gravity. That’s why astronauts are often carried out of the capsule after landing—they could pass out from the sudden shift.
Interestingly, anecdotal evidence initially suggested that women might experience more difficulty with orthostatic intolerance than men. However, those observations came from small sample sizes, and we need much more data to conclude.
At the same time, there are also anecdotal suggestions that women might be more resilient to certain other space-related stressors. As more female astronauts go on longer-duration missions, we’re starting to gather better data and do more comprehensive comparisons. When Scott Kelly went to the ISS, no U.S. astronaut had spent more than a year in space. Since then, many more astronauts—both men and women—have completed six-month or longer missions, so we're in a better position now to study gender-based physiological differences in a meaningful way.
Q: How do women astronauts manage menstruation during long-term space missions? Have there been any observed changes to the menstrual cycle in space?
A: That’s a really good question. I haven’t personally seen any published studies specifically addressing menstrual cycle changes in space. The medical records do exist, but I don’t have access to those confidential reports. That said, this is an area where more research should ideally be made public because it's a relevant physiological issue that deserves attention.
Q: Speaking of women astronauts, Sunita Williams recently had an extended and somewhat unexpected mission. Have you had a chance to analyse any data related to her case? Also, what kinds of psychological or physiological changes can occur during such unplanned, extended missions, especially given your psychiatry background?
A: Yes, unplanned or extended missions definitely introduce additional layers of psychological stress. Being away from family, confined in a limited space for long periods—all of that adds up. On top of that, there are cognitive and neurological changes that researchers are studying closely.
There have been some recent papers on changes in gene expression in the brain following long-duration space missions, which may impact cognition. However, studying cognitive changes in astronauts is particularly challenging. Most Earth-based cognitive tests are too easy for astronauts, who tend to ace them even under stress. So, NASA has been developing specialized cognitive assessments specifically for astronauts.
Q: It seems like a lot of space research isn’t just for astronauts—it can help us on Earth too. What insights from your studies on fluid shifts and vascular changes in astronauts might have applications here on Earth?
A: Absolutely. Many of the physiological changes we observe in astronauts—like fluid shifts, vascular stiffening, and muscle or bone loss—mirror conditions we see in aging or bedridden patients on Earth. Studying how these changes occur in microgravity helps us better understand how similar processes happen down here.
For example, understanding how blood redistributes in the body without gravity could inform better treatments for conditions like orthostatic hypotension or oedema. And studying bone density loss in astronauts helps us develop new treatments for osteoporosis. So, the insights gained from space medicine are very much applicable to improving human health on Earth.
Q: Astronauts face several challenges in space, but do they also gain any physiological or molecular advantages from long-duration spaceflight?
A: That’s an insightful question. Interestingly, when we compared the twin astronauts Scott and Mark Kelly during the NASA Twin Study, we saw some surprising benefits.
Scott, who was in space, followed a highly regimented lifestyle—consistent exercise, a controlled diet, and a structured daily routine. As a result, many of his physiological markers, like lipid levels and cardiovascular risk indicators, remained stable throughout the mission.
In contrast, Mark, who remained on Earth, showed more variability in these same markers—similar to what you’d expect from an average middle-aged person in America. So in a way, the astronaut lifestyle—with its emphasis on physical activity, cognitive engagement, and controlled nutrition—does support certain aspects of healthy aging.
