Spaceflight mirrors – A NASA twin study found that Scott Kelly’s year on the International Space Station boosted inflammation and disrupted mitochondria—signs tied to ageing. Follow-up work links long missions to multiple “hallmarks of ageing,” and researchers argue that the same s
When Scott Kelly left Earth for a mission that ultimately lasted 340 days, he wasn’t just packing for space. He was stepping into an environment known to rewrite biology—slowly, systematically, and in ways that can look eerily familiar on the ground.
In the twin paradox. one brother races into space while the other stays home. and when the traveler returns. he’s still young. Real life can’t match the thought experiment’s near-light speeds. But real life does offer something close: the aging shift runs in the opposite direction. A twin who spends six months in space can, by some measures, age about 40 times faster than their earthbound sibling.
That detail matters because the factors that accelerate aging in orbit are no longer confined to astronauts. The good news, researchers say, is that attempts to protect crews going to the International Space Station—and eventually beyond—may point to ways to protect everyone else.
As of now, depending on how you draw the boundary, some 781 people have been into space. Some spent only hours or days there. Around half lived on a space station for months. A trip to the International Space Station—undertaken by nearly 300 astronauts—usually means spending six months or more in space.
NASA has long worried that extended time in orbit can harm health. With lengthy missions to Mars and beyond already on the table, the agency has focused on both understanding the effects and finding ways to reduce them.
One of the best-known results came from the NASA twin study. In 1996, NASA recruited two identical twin brothers, Scott and Mark Kelly, into the astronaut corps. Both flew on shuttle missions. Scott later spent time on the ISS. Mark retired in 2011, but Scott carried on—then NASA selected him for a year-long stint on the ISS in 2015.
The study was built around a classic experimental idea: twins help separate environmental effects from genetics. Ideally, researchers would have had hundreds of twin pairs. That wasn’t possible here. Still, a sample size of two, the researchers decided, could be more informative than doing nothing at all.
Before, during and after the flight, blood, urine and faeces were collected from both twins. The findings included clear differences in inflammation markers. After a year in space, Scott showed elevated levels of several inflammatory molecules, alongside decreased levels of anti-inflammatory ones. He also showed signs of mitochondrial dysfunction.
Those changes line up with one set of warnings from aging research. Both are among 12 “hallmarks of ageing,” pointing to the possibility that living in low gravity can accelerate senescence. Subsequent research on other astronauts expanded the list further: extended stays in space have been linked to at least four more of the hallmarks.
Astronauts, researchers have reported, also show genomic instability, shifts toward an unhealthy gut microbiome, disturbances in the endocrine system, and blunted sensing of nutrients.
The biological signals translate into body-level changes as well. Astronauts can display physiological signs of accelerated aging—sometimes sharply—such as steep declines in cardiovascular health, loss of muscle tissue and bone, cognitive problems and immune dysfunction.
Cardiovascular impacts have been particularly striking. By one measure of cardiovascular health, the stiffness of the carotid artery can reach an “age 20 years” level in just six months.
The question is what drives those shifts. Daniel Winer, at the Buck Institute for Research on Aging in California, points to four features of living in space that accelerate aging.
First is the lack of gravity. With less load on muscles and bone, both atrophy. Second is a compressed dark-light cycle. On the ISS, occupants experience 16 sunrises and 16 sunsets every 24 hours, throwing a huge wrench into circadian rhythms. Third is exposure to high doses of ionising radiation from galactic cosmic rays—equivalent to 480 chest X-rays over six months. The fourth factor is social isolation.
Winer says all of these are known to be causal in aging.
“So what?” is the instinct many people have when they hear about astronauts. Most Earthbound lives don’t include galactic cosmic rays or months of microgravity. But the stressors that matter aren’t as distant as they sound.
According to Winer, conditions on Earth can replicate parts of the space environment. People don’t experience microgravity, but sedentary lifestyles create the same muscle and bone effects. Circadian disruption and social isolation are common. And millions of people are exposed to high levels of ionising radiation from naturally occurring radon gas.
The mechanisms of ageing remain opaque. Still, researchers see a practical path forward. Studies on long-stay astronauts, Winer says, can help clarify why the biology turns the way it does.
Astronauts, he argues, make an effective model organism for studying aging. In a recent review article. he and his colleagues wrote that spaceflight exposures can be understood as acute. intensified versions of chronic. lower-grade stressors that drive a substantial portion of age-associated decline in terrestrial populations.
That idea offers more than a scientific puzzle. It suggests a route to the “elusive goal” of geroscience—anti-ageing interventions that act on the processes that cause age-related decline, not just on the symptoms.
NASA, understandably, has a strong incentive to protect its employees. The agency has collaborated with Winer’s team to find molecules to counteract pro-ageing effects of space flight. Over the past 70 years, the space programme has already produced multiple medical spin-offs, including cochlear implants and artificial limbs.
A fountain of youth would be a dramatic addition to that list—and for now, it starts with something much less glamorous but far more useful: watching how the body ages in space, then taking those lessons back to Earth.
NASA twin study Scott Kelly Mark Kelly ISS spaceflight ageing mitochondrial dysfunction inflammation hallmarks of ageing carotid artery stiffness circadian disruption ionising radiation radon gas geroscience