Last year, various media outlets fumbled their reporting of genuinely interesting research from NASA, one that hoped to start figuring out what happens to our bodies if we live in space for long periods of time. The study was a meticulous comparison of then 50-year-old astronaut Scott Kelly, who spent a year aboard the International Space Station in 2015, and his identical twin brother Mark Kelly, who stayed on Earth.
This Thursday, the final findings of the NASA Twins Study were published in Science, and they’re still plenty cool—if a little anticlimactic when measured against the media hype the research got a year ago.
NASA found that Scott Kelly was about as mentally, physically, and genetically healthy as his brother during his trip to space, and that the vast majority of small changes spotted in Scott (relative to himself before the mission) went back to normal within six months time. But the differences seen in Scott while up in space and after his return home could provide NASA important leads on how to keep astronauts safe during longer missions to Mars and beyond.
“I think it’s reassuring to know that when you come back things will largely be back to the same,” Michael Synder, one of the study’s 10 principal investigators and director of the Stanford Center for Genomics and Personalized Medicine, said at a press conference held Tuesday discussing the results.
Preliminary results from the study were released in 2017. But it was the second round of findings, released in January 2018, that really caught the attention of media outlets, some of which misrepresented what was found. In particular, outlets like Newsweek reported that a whopping “seven percent of [Scott Kelly’s] genes did not return to normal after he landed.” Others implied that Scott Kelly had become a different person from his twin brother.
But the researchers were never talking about a seven percent difference between the twins’ genes. They were saying that some of Scott Kelly’s genes had changed in their expression—the carrying out of instructions in a cell’s genome—during his time up in space. And that roughly 7 percent of this overall change in gene expression could still be seen six months after he returned home.
That remaining change in gene expression six months out was actually closer to 10 percent, involving hundreds of individual genes related to the immune system and elsewhere, according to the final paper in Science. But as NASA clarified during the hubbub last year, this was still a relatively tiny change in his gene expression, or “epigenetics” as it’s otherwise known. These epigenetic and other changes to his metabolism or immune system were also well within the range you’d expect to see from someone dealing with a decent amount of stress, like intense exercise.
“Given that the majority of the biological and human health variables remained stable, or returned to baseline, these data suggest that human health can be mostly sustained over this duration of spaceflight,” said NASA in a statement.
Indeed, Mark Kelly also had epigenetic changes during the whole study period, and even to a slightly greater degree than his spacebound brother. That’s not so surprising, because literally everything in our environment can shape our gene expression. And while space is a stressful experience that can wear down the body and immune system, Scott Kelly wasn’t doing other things known to negatively affect the body that his brother was doing on Earth, like drinking alcohol.
The changes detected in Scott relative to himself on Earth and his brother are important though, since they help us get a sense of how long-term space travel will affect the human body. Scott’s eyes, for instance, developed a thicker retinal nerve after a few months, which has been noticed with some but not all astronauts on longer missions. The change is probably mostly caused by the microgravity of space. But scientists suspect that genetics play a part in making astronauts more vulnerable to it. As evidence for that hunch, both twins had genetic variations linked to the eye change, though only Scott developed it.
There were also unexpected shifts to Scott Kelly’s telomeres, the endcaps of chromosomes that are thought to predict our cellular age since they shorten over our lifetime. Some of them got longer while Kelly was in space, but then quickly shortened soon after his return and six months later, some remained shorter than before. It’s too early to say what any of that really means. But study author Susan Bailey, a radiation biologist at Colorado State University, cautioned during the press conference against anyone thinking that space travel should “be viewed as the fountain of youth and that people might expect to live longer because they’re in space.”
Interestingly, while most of Scott Kelly’s health stayed unchanged or returned to normal after he came back, his brainpower—measured by how accurate and speedy he was on cognitive tests—did take a noticeable step down once he returned, which was still apparent six months after his return. It’s unclear just how much of this mental drain can be attributed to the hazards of space itself, though, according to principal investigator Mathias Basner, an associate professor of sleep and chronobiology in psychiatry at the University of Pennsylvania’s Perelman School of Medicine.
“It could be the effects of being re-exposed and readjusting to the gravity on Earth,” Basner told Gizmodo, noting that Kelly himself complained about learning to walk normally again. “But also, his post-mission schedule was very hectic, with lots of media events.”
That said, there’s also still the possibility that the conditions of the trip itself, including length, contributed to Kelly’s sharpness falling. And that’s an important risk to keep an eye on once people start taking even longer, more isolated missions.
“Of course, it is a potential red flag. I mean, if we send a group or astronauts to Mars, the journey there will probably take about a year. And then they have to go through this mission critical phase on the surface of Mars when we really want them to perform their best,” said Basner. “This study, admittedly with a n of 1, suggests that they may not be able to do that.”
Pivotal as the NASA Twins Study is, it’s only the start of studying human health in space. Living on the ISS is no picnic, for instance, but astronauts there are still largely protected from the cosmic radiation that would bombard any visitors on their way to Mars (the total radiation exposure would be at least fivefold greater). And the Kelly twins are the very epitome of a small sample size. So we need lots more research, with more astronauts. To that end, NASA is planning more missions of varying lengths up to a year that should provide more data as to the effects of space on the body.