Scott Kelly holds the record for the longest consecutive time spent in space by an American astronaut. When he touched down to Earth in March 2016, he’d spent 340 days rotating the planet on the International Space Station. During that time, and after his return to earth, several scientists closely tracked his health — monitoring the effects of the extended time in space on his cognition, gut microbes, genetics, heart, and more.
“Within that year, we wanted to measure everything we possibly could,” says Chris Mason, from Weill Cornell Medicine, who studied the astronaut’s genetics and epigenetics.
The data Mason and other researchers collected add valuable information to our understanding of how the human body changes under the stress of space, with implications for missions to Mars and beyond. They also provide insights into the biology of a healthy body that may be extrapolated outside of the boundaries of the space program.
Scott has a twin, Mark, who stayed earthbound and served as a near-perfect control for the study: someone with the same genetics as Scott. Preliminary data comparing samples taken from the twins, published in early 2017, showed that Scott’s telomeres had gotten significantly longer during his time in space. Telomeres protect DNA from unraveling by capping the ends of chromosomes, and normally shrink with age. But while on board the International Space Station, Scott’s genes were also expressed differently. Like a volume knob, the information from his genes was turned up in some cases and down in others. This resulted in changes in proteins and metabolites that indicated oxygen deprivation stress in Scott’s body, as well as increased inflammation and variations in his nutrient levels.
In January 2018, NASA announced that researchers had updated these findings to include information collected after Scott returned to Earth. Most of the biological changes Scott experienced, including the elongated telomeres, had returned to normal levels. But even after six months, the levels of 7 percent of his genes remained different than they were before the mission.
The results generated a lot of excitement and media frenzy. Some reports over the last week might have you believe that 7 percent of Scott’s genes — full stop — were different. However, if that was the case, Scott would be a different species. The twins are, still, identical twins.
The truth is researchers expected to see many of these changes in Scott. Adapting to new environments generally leads to changes in the body — biochemically, molecularly, and genetically. And the high-radiation environment and microgravity that astronauts are exposed to in space requires a lot of adjustment, Mason says. “It’s stressful up there, there’s no time to take a few days’ vacation.”
But it’s hard to say what the changes actually mean. Scott doesn’t have any measurable, clinical health problems. Mason can’t say if the percent difference in gene expression, for example, is high or low for space travel. “It’s the first time we’ve ever looked at this in humans,” he says.
Scientists don’t have much baseline information for gene expression fluctuation in healthy humans. So it’s hard to establish the potential repercussions, positive or negative, of the changes seen in Scott Kelly — there’s nothing to compare it to. “We don’t know if the changes mean a change in health risk or health status,” says Dana Dolinoy, who studies epigenetics and the environment at the University of Michigan.
Studies that provide that kind of data are difficult. They involve tracking multiple biological measures for weeks, months, or years at a time. “We do monitor some people for long periods of time. We monitor cancer patients, for example, but obviously, they’re sick,” Mason says. Gathering so much data from healthy subjects was one of the valuable contributions the twin study made, he says. “It’s a benchmark, not just for us, but for everyone else.”
Mason plans to compare data from the Kelly twins to that available from long-term monitoring of patients with major medical problems, like sepsis or a heart attack. It might show researchers if these gene expression changes are the way the body would respond to any large stress, or if they were specific to Scott’s time in space, Mason says. “It’s not the same, but it might be useful to see how the body responds to a large stressor,” he says.
Genetic and epigenetic changes, overall, can be long-lived, Dalinoy says. “It’s not just about how things change now, it’s how the trajectory changes,” she says. “There are known age-related changes in the epigenome. But if an environmental exposure like this changes the rate of those changes, it could be that when you’re 80 years old, you’re in a place where you’re not expressing enough of a particular gene.”
That’s why Dalinoy says she’d like to see more, longer term data from the Kelly’s. “I’d like to see what’s happening five, 10 years out.” But, she notes, that requires the investment of more time and more energy. “This is the problem with studying humans,” she says. “It takes a long time.”