Only about 600 people have ever traveled to space. The vast majority of astronauts in the past six decades have been middle-aged men on short missions of less than 20 days.
As private, commercial and multinational space providers and pilots enter the market, we are witnessing a new era of human spaceflight. Missions range from minutes, hours, days to months.
As humanity looks forward to returning to the moon in the coming decade, space exploration missions will last much longer, with many more space travelers and even space tourists. This also means that a greater diversity of people will experience the extreme environment of space — more women and people of different ethnicities, ages and health statuses.
Because people respond differently to the unique stressors and exposures of space, space health researchers like me are trying to better understand the effects of spaceflight on human health. With such information, we can figure out how to help astronauts stay healthy, both during their time in space and when they return to Earth.
As part of the historic NASA Twins Study, my colleagues and I published groundbreaking research in 2019 on the effects of one year aboard the International Space Station on the human body.
I am a radiation oncology biologist in the Department of Environmental and Radiological Health Sciences at Colorado State University. Over the past few years, I have been building on that earlier research in a series of papers that have recently been published in the Nature journal portfolio.
These papers are part of the Space Omics and Medical Atlas package of manuscripts, data, protocols and repositories that form the largest collection ever for space medicine and space biology. More than 100 institutions from 25 countries have contributed to the coordinated release of a wide range of spaceflight data.
The NASA Twins Study
NASA’s Twins Study seized a unique research opportunity.
NASA selected astronaut Scott Kelly for the agency’s first year-long mission, during which he spent a year aboard the International Space Station from 2015 to 2016. During the same period, his identical twin brother, Mark Kelly, a former astronaut and current U.S. senator from Arizona, remained on Earth.
My team and I examined blood samples collected from the twin in space and his genetically matched twin on Earth before, during, and after spaceflight. We found that Scott’s telomeres—the protective caps at the ends of chromosomes, similar to the plastic tip that keeps a shoelace from fraying—had unexpectedly lengthened during his year in space.
When Scott returned to Earth, however, his telomeres shortened rapidly. Over the next few months, his telomeres recovered, but they were still shorter after his trip than they had been before he went into space.
As you age, your telomeres shorten due to a variety of factors, including stress. The length of your telomeres can serve as a biological indicator of your risk for developing age-related conditions such as dementia, heart disease, and cancer.
In a separate study, my team studied a cohort of 10 astronauts on six-month missions aboard the International Space Station. We also had a control group of participants of the same age and gender who remained on the ground.
We measured telomere length before, during and after spaceflight and again found that telomeres were longer during spaceflight and then shorter upon return to Earth. Overall, the astronauts had many more short telomeres after spaceflight than before.
One of the other Twins Study researchers, Christopher Mason, and I conducted another telomere study—this time with twins who were high-altitude mountain climbers—in a somewhat similarly extreme environment on Earth.
We found that the climbers’ telomeres were longer while ascending Mount Everest, and that they shortened after descending. Their low-altitude twins did not experience the same changes in telomere length. These results indicate that it is not the microgravity of the space station that led to the telomere length changes we observed in the astronauts. Other culprits, such as increased radiation exposure, are more likely.
Citizens in space
In our latest study, we looked at telomeres of the crew aboard SpaceX’s 2021 Inspiration4 mission. This mission had the first all-civilian crew, whose ages spanned four decades. All crew members’ telomeres lengthened during the mission, and three of the four astronauts also showed telomere shortening when they returned to Earth.
What’s particularly interesting about these findings is that the Inspiration4 mission lasted only three days. So not only do scientists now have consistent and reproducible data on how telomeres respond to spaceflight, but we also know that it happens quickly. These results suggest that even short trips, like a weekend getaway to space, are associated with changes in telomere length.
Scientists still don’t fully understand the health effects of such changes in telomere length. We need more research to understand how both long and short telomeres can affect an astronaut’s long-term health.
Telomere RNA
In another paper we showed that the Inspiration4 crew – as well as Scott Kelly and the high-altitude mountaineers – showed increased levels of a telomere RNA called TERRA.
Telomeres are made up of many repetitive DNA sequences. These are transcribed into TERRA, which contributes to telomere structure and helps them do their job.
Together with laboratory studies, these findings tell us that telomeres are damaged during spaceflight. While there is much we still do not know, we do know that telomeres are particularly sensitive to oxidative stress. So the chronic oxidative damage that astronauts experience when exposed to space radiation all day is likely contributing to the telomere responses that we see.
We also wrote a review article with a more futuristic perspective on how a better understanding of telomeres and aging could impact the ability of humans to not only survive long-term space travel, but to thrive and even colonize other planets. To do that, humans would need to reproduce in space, and future generations would need to grow up in space. We don’t know yet if that’s even possible.
Plant telomeres in space
My colleagues and I also did other work on the Space Omics and Medical Atlas package, including a paper published in Nature Communications. The research team, led by Texas A&M biologist Dorothy Shippen and Ohio University biologist Sarah Wyatt, found that plants that flew in space, unlike humans, did not have longer telomeres during their time aboard the International Space Station.
However, the plants did increase their production of telomerase, the enzyme that maintains telomere length.
As anyone who has seen “The Martian” knows, plants play a vital role in the long-term survival of humans in space. This finding suggests that plants may be naturally better suited to withstand the stressors of space than humans.
This article is republished from The Conversation, an independent nonprofit organization that brings you facts and analysis to help you understand our complex world.
It is written by: Susan Bailey, Colorado State University.
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Susan Bailey receives funding from NASA.