A fascinating batch of new research papers are highlighting the various health risks associated with long-duration space missions, including troublesome observations having to do with the aging process and radiation-induced DNA damage.
Space, as we’re learning, really sucks for us puny humans.
Without gravity perpetually pulling us downward, and without a protective atmosphere to shield us from the Sun’s deadly rays, we become exposed to a plethora of health risks—things like loss of bone density and muscle mass, cardiovascular and neurological problems, and even eye disorders. And it seems the longer we stay in space, the more severe the impacts. This could throw a serious monkey wrench into our plans to conquer deep space, whether it be to build bases on the Moon and Mars or journeying to the outer solar system and beyond.
Sadly, the risks don’t stop there. A gigantic package of 30 research papers were released today across five Cell Press journals, all having to do with the health concerns posed by long-duration space missions. Collectively, these papers represent “the largest set of space biology and astronaut health effects data ever produced,” according to a Colorado State University press release.
These new studies of astronauts and model organisms have revealed six potentially detrimental aspects of long-duration spaceflight: oxidative stress (an imbalance of free radicals and antioxidants leading to tissue damage); DNA damage; mitochondrial dysfunction (mitochondria are the power packs of our cells); telomere length alterations; changes to the genome and epigenome (i.e. environment-influenced gene expression); and changes to the microbiome (the totality of microorganisms living outside and inside our bodies).
Of these, two in particular grabbed my attention: telomere length alternations and DNA damage. All six health features listed in the new studies play a profound role when it comes to our health, but telomeres and DNA damage in particular can be linked to the aging process.
Telomeres are the protective caps located on the ends of chromosomes (threaded structures in the nucleus of cells that carry our genes). Telomeres get progressively shorter as a person ages, and significant changes to the length of these caps can be taken as a sign of accelerated aging and/or heightened risk of developing age-related diseases like cancer, cardiovascular disease, and dementia.
That exposure to space alters the length of telomeres is not a surprise. Prior research involving identical twin astronauts Scott and Mark Kelly (Scott spent nearly a year in space while his brother stayed on the ground) showed that, for Scott, the telomeres in his white blood cells became elongated while in space, but they basically returned to normal once he returned to normal gravity conditions.
Susan Bailey, a biologist from Colorado State University and a veteran of the pioneering twin study, has now co-authored a new paper, published in Cell, in which her team studied 10 other astronauts, all of whom flew on long-duration missions aboard the ISS. And by long-duration missions, we’re typically talking about stints lasting around six months or longer.
Blood samples were taken from the astronauts before and after their stays on the ISS. Just like in the twin study, long-term exposure to space resulted in the elongation of telomeres. In this case, however, the researchers also found that the astronauts, in general, had shorter telomeres after their missions. Biologists refer to this as ALT, or the alternating lengthening of telomeres—and it wasn’t something they expected, as it’s typically seen in cancer cases or in developing embryos. Upsettingly, ALT was observed in all 10 of the astronauts studied.
Now, the lengthening of telomeres may sound promising as far as extended longevity is concerned, but as Bailey explained in an email, this should not be construed as good news.
“Both short and long telomeres are associated with increased disease risk,” said Bailey. “Short telomeres are associated with accelerated aging and the associated degenerative pathologies like cardiovascular disease and some cancers.”
Long telomeres can be associated with longevity, she said, “but they are also associated with cancer,” because mutated cells live longer, which increases risk. The 10 astronauts exhibited dramatic shifts in telomere length over time, but the researchers don’t yet know the associated health effects.
“Longer telomeres during spaceflight, rapid shortening upon return to Earth,” she summarized. “And overall, they ended up with shorter telomeres than they started out with,” adding that “individual differences in response were also observed.”
As to the cause of the wonky lengths seen in the telomeres, Bailey pointed the finger at chronic oxidative stress.
“Acute exposures to ionizing radiation have been shown to cause oxidative stress,” explained Bailey. “In the space radiation environment, chronic exposures would be associated with chronic oxidative stress” and telomeres “are very susceptible to oxidative damage.”
As the new research also shows, exposure to space results in DNA damage. In particular, the scientists documented chromosomal inversions, which are signatures of radiation exposure. Chromosomal inversions happen when “two breaks occur within the same chromosome and the genetic material in between the breaks is inverted,” according to ScienceDirect.
“Consistent with chronic exposure to the space radiation environment, inversions were elevated during spaceflight for all crewmembers,” said Bailey. “And increased frequencies of inversions persisted after spaceflight—potentially indicative of genome instability and/or clonal hematopoiesis,” which is an increased cancer risk.
The long-term health effects of space missions will continue to be Bailey’s primary focus, including ongoing investigations into telomere length dynamics (how it changes over time) and persistent DNA damage, which in this case involved the chromosomal inversions—biomarkers associated with cancer and cardiovascular disease.
To that end, this team will be participating in NASA’s One Year Mission Project, which according to Bailey will be called CIPHER. For that project, the team will conduct similar studies, in which they’ll monitor telomere length dynamics and DNA damage among astronauts involved in long-duration missions.
This work is so very important, because it could eventually lead to medical interventions that will allow for safer long-duration missions. The humble tardigrade, for example, can tolerate large doses of radiation. We might eventually find a way to adapt this ability to ourselves. Indeed, in order for us to live and work in space, we’ll have to become a bit less human.