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For nearly a year, NASA astronaut Scott Kelly was a human satellite, spinning 240 miles above Earth in zero gravity, drinking recycled urine and once getting lost in space.
His incredible journey was genetically and physiologically stressful, according to long-awaited test results in a landmark study. But it’s not clear what all the biological changes mean. And most did not persist, with nearly all reverting to preflight levels after his return.
The research — comparing Scott’s body to that of his earthbound identical twin, Mark, also an astronaut — is a crucial first step to understanding health risks as humans venture longer and deeper in space — to the moon and even Mars. The effort, coordinated by NASA’s Human Research Program, is published in Friday’s issue of the journal Science.
“There are dramatic changes that occur as someone goes in space,” said Stanford geneticist Michael Snyder, who analyzed all of the biomedical and molecular data collected from 10 different teams of 84 researchers across 12 universities to produce a single, comprehensive view of how Scott’s body responded to spaceflight.
“But it’s reassuring to know that when you come back things will largely be back to the same,” Snyder said in a teleconference with reporters Thursday. “Scott is back to virtually normal.”
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One of the study’s surprising results included Scott’s dramatic in-flight lengthening of telomeres, the protective endcaps on chromosomes that signal whether a person is at risk for accelerated aging or illness. Because telomeres typically shorten as a person ages, this suggests that his cells were becoming more youthful. While most of his telomeres returned to near pre-flight averages, he now has more short telomeres than he did prior to the 340-day mission. It is not known if this is space-related or part of normal aging.
Scott experienced different changes in gene expression than Mark. While Scott’s actual genes weren’t altered, some, such as those that encode proteins that help fix damaged DNA, became more active. More than 90 percent of Scott’s gene expression levels returned to normal or baseline levels within six months of landing back on Earth. It is not known if these changes are indicative of space flight alone, or if they might have occurred normally.
The scientists also found thickening of Scott’s carotid artery and signs of increased stress levels. A metabolite called lactate, associated with diabetic kidney disease, was increased in Scott in spaceflight but reverted to normal levels when he returned to earth. He also lost 15 pounds.
In his gut, the balance of microbes shifted. But this was no different than the stress-related changes that we experience on Earth, scientists said.
His eyeball shape changed over the course of the flight, a familiar syndrome that’s common in astronauts and thought to be caused by fluids shifting in the absence of gravity.
There were some cognitive changes — not in space, but upon his return. In his 2017 memoir “Endurance,” Kelly said he suffered flu-like symptoms and insomnia after landing on Earth, and many things competed for his attention.
The flu vaccine given to Scott in space worked exactly the same as on Earth, according to work done by Stanford’s Dr. Emmanuel Mignot. This is reassuring news should a vaccine ever be needed during long-duration missions.
Mark’s data was used as a basis of comparison — and showed just normal levels of variance. Compared to Scott while in space, his tests showed fewer signs of genetic stress, inflammation and altered metabolism. Mark gained weight, while Scott lost it. His telomere lengths were stable and there were no significant cardiovascular changes.
Scott and Mark Kelly, now 55, offered an exceptional opportunity to study how the body responds to space travel. The brothers are the only known siblings to have both traveled in space. During Scott’s year-long mission at the International Space Station in 2015, Mark, who retired from spaceflight in 2011 after four shuttle flights, led an equally busy life in Arizona.
For a year, Scott did not see his family, feel the sun or wind on his face or taste fresh-cooked food. His days were long and tightly controlled. He was exposed to 48 times more radiation than the average exposure on Earth over the course of a year. The spacecraft’s carbon dioxide levels were higher than on Earth. On one space walk, while working on a valve in an unfamiliar area, he got turned upside down, lost and disoriented.
Scott Kelly performing the Cognition test battery on board the International Space Station. [Credit: NASA]In contrast, Mark socialized, played golf, drank alcohol and led an active public life. He’s an author, political activist, aerospace consultant and the husband of former U.S. Representative Gabrielle Giffords, shot in an attempted assassination. He is now running for John McCain’s Senate seat in Arizona.
Because identical twins share the same genetic makeup, they are physically very similar. Scott provided a test case to measure in space; Mark providing a baseline test case on Earth. Scientists collected blood samples, physiological data and cognitive measurements from the brothers for six months before the trip, and nine months after.
Collecting Scott’s samples during the mission was tricky – scientists had to develop a method for them to be collected at zero gravity, frozen, sent from the space station, land in a location in Asia and brought to a lab for processing within 48 hours.
Scientists pored over his most intimate secrets: the sequence of his DNA, the RNA and proteins produced by his cells, the metabolites and signaling molecules wafting through his blood. They spied on his immune system as it dealt with stress and battled viral infections.
The composite result of the many different findings — assembled by Snyder’s lab at Stanford — was a dynamic picture of how Scott’s body responded to illness and disease. Snyder’s lab has pioneered the use of such large scale and simultaneous analyses.
“It is complicated to try to bring together so many different data types,” said Snyder, who is also the director of the Stanford Center for Genomics and Personalized Medicine. “It’s like a mix of apples and oranges and bananas. Somebody has step step back and say: These are all fruits. Then try to make sense of it.”
NASA said the changes were likely within the range for humans under stress, such as intense exercise. Some of the changes in gene activity, such as those involved in bone formation or DNA repair, were expected because it is well known that astronauts experience reductions in bone density in zero gravity as well as increased exposure to DNA-damaging radiation during the flight.
“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,” according to NASA.
Research on additional astronauts — in far more adverse conditions — could eventually help scientists predict the types of medical risks the astronauts face on longer space journeys with greater exposure to radiation, lower gravity, more limited diet, greater isolation, less exercise and more disrupted sleep cycles.
NASA has announced plans for a mission to Mars and to a “cis-Lunar station,” between the Earth and the Moon, which will provide new opportunities for studying what happens to the human body during extended spaceflight.
Snyder offered this advice for anyone seeking to travel in space:
“I do think you should be prepared,” he said. “If you’re going into a stress environment, you do expect your body to go through lots of different changes.
“But it’s good to know that you still can function fine,” he said, “that things are still working normal.”
