NASA study highlights profound effects of space travel on human body

Scott Kelly lived in space for over a year while his twin stayed on Earth.

NASA released the results of a momentous twin study on Thursday, which found that space travel has profound effects on the human body. The findings could shape NASA’s 2020 mission to Mars — a journey that would take astronauts at least three years.

Astronaut Scott Kelly was separated from his astronaut twin brother Mark Kelly on March 27, 2015. Scott Kelly lived on the International Space Station — while his brother lived on Earth — and returned on March 1, 2016. Three years later, the results of the study, announced from NASA’s Houston headquarters, showed that long-term space missions are likely to cause major changes to astronauts’ metabolisms, genetics and cognitive performance. What’s more, the changes could last months after astronauts return to Earth, if not longer.

Space presents unique stresses to the human body. With lower gravity levels, for example, bones and muscles are more likely to become weak since they no longer have to support the weight of the body. Space flight also affects astronauts’ eyes, causing what’s now called space flight-associated neuro-ocular syndrome, characterized by swelling in the optic nerve head, among other symptoms.

Astronauts in space are also exposed to higher levels of radiation without the Earth’s atmosphere there to act as a filter. Dr. Christopher Mason, study investigator and associate professor of physiology and biophysics at Weill Cornell School of Medicine, told ABC News that radiation levels "are about eight times higher" on Mars than they are on Earth.

Until this study, the majority of astronaut research had only looked at space missions lasting six months or less. Writing for The Sydney Morning Herald in 2017, Scott Kelly said that by the end of his mission, he had spent a career total of 520 days in space, "more than any other NASA astronaut.”

During a news conference on Thursday, Scott Kelly said he was ready to go back to space again. "Put me in coach," he said. "I'm ready."

Since the Kelly brothers are genetically identical, researchers were able to control for genetic differences in their study, so that “the only changes that [we] would see would be because of environmental changes,” senior author Brinda Rana, PhD, professor of psychiatry at the UC San Diego School of Medicine told ABC News.

“The study provided insight into the body’s response to space flight…[and] captured an integrated view on the molecular, behavioral and physiological changes experienced by a middle-aged man on Earth over a two-year period,” Rana said in a press release.

By the end of the mission, Scott Kelly had clear signs of DNA damage, dehydration, and cognitive decline, the researchers found. Many of his telomeres — stretches of DNA that protect our genetic data and have been associated with a person’s lifespan — were also shorter.

“This may represent the way the body compensates to counteract some of the effects of space,” Rana said, noting that the DNA damage was due to the radiation Scott Kelly was exposed to in space.

Several months after his return to Earth, Scott Kelly continued to exhibit these effects of space on his body. Although it’s unclear how permanent these effects are — or if they’re even totally related to his time in space — the study has prompted NASA to dig deeper. As the organization prepares for the mission to Mars, Rana said that “NASA has expanded [this] study to a larger group of astronauts, and is planning to send up another group.”

Navjot Kaur Sobti is an internal medicine physician at Dartmouth Hitchcock Medical Center/Dartmouth School of Medicine and a member of the ABC News Medical Unit.