Down to their very DNA, astronauts’ bodies can change in weird and sometimes significant ways, particularly during a long flight high above the Earth: They start to elongate, often developing a taller “space height” and because human bodies are mostly liquid, redistribution of fluids may also give them “chicken legs” and a “puffy head.” Once they’re back, that all starts to readjust.
Doctors will be keeping all of this in mind as astronauts Barry “Butch” Wilmore and Suni Williams return on Tuesday from nearly nine months in space.
Scientists are still figuring out the long-term health effects of spending a lot of time in space, but decades of data show that astronauts undergo physical changes after even a brief period. Most of those changes will reverse themselves shortly after they return to Earth.
“There is some individual variability on how quickly they recover, but it is pretty impressive to see how they will turn the corner and really adapt quickly,” Dervay said. “Oftentimes, if you look at them a couple days later, you really have no idea what they’ve just done for the last several months.”
Microgravity is behind many of the changes that astronauts can experience.
Without the pull of Earth, astronauts can lose bone density, and their muscles begin to waste away. They can lose motor control, coordination and balance in space, developing a kind of motion sickness, studies show. A lack of gravity can also affect their immune and cardiovascular systems, their vision and their very DNA.
Most of the effects seem to be short-lived — only a handful of health issues have so far been found to linger — and the astronauts can look forward to a lot of rehab exercises on Earth to get their bones and muscles back into shape.
Although Wilmore and Williams weren’t initially expected to stay on the International Space Station as long as they did – their initial trip was supposed to last only eight days – NASA leaders don’t believe the two will have any unusual health problems because of it.
“We don’t see any need for any special precaution,” Dina Contella, deputy manager of NASA’s International Space Station Program, said Friday. “Like any astronauts coming back, there is an acclimation period, and so that will vary by crew member.”
Muscle and bone deterioration
Without gravity for the body to move against and with the body exposed to radiation in space, muscle atrophy and dysfunction can happen to even the fittest astronaut. NASA has found that astronauts’ bodies can experience one-third reduction in muscle fiber size in less than two weeks.
In a single month in space, an astronaut might also lose up to 1.5% of their bone mass – about as much as a postmenopausal woman who is not in treatment loses in about a year. Such loss can make people vulnerable to fractures and lead to premature osteoporosis, but more research is needed to learn whether the bone loss persists long after the space flight.
To help mitigate bone and muscle problems, astronauts eat a special diet and do about 2½ hours of exercise daily, on average. They can use a treadmill or a stationary bike, but they also have a special Advanced Resistive Exercise Device that mimics weightlifting on Earth.
“We try to keep the bone strong and muscles strong to minimize any effects of microgravity,” Dervay said. “Plus, from a psychological perspective, it’s outstanding because it gives them that break during the day, and they know they’re doing something for themselves.”
NASA has been researching whether aerobics and resistance exercises would be as helpful as a treadmill, since the spacecraft needed for future long-distance flight may not be able to accommodate heavy exercise equipment.
Dervay says the body is “brilliant” in the way it adjusts to microgravity, but “we want to ensure that when we bring them home, they’re in the best position they can be to return … and get back into the normal flow of their lives.”
Astronauts may view one physical change to their bones as a benefit: Without the pull of gravity, a person’s spine straightens, and they grow taller.
NASA says the height of a crew member can increase 3% over the first three or four days of weightlessness. Astronaut Kate Rubins, for example, went from 5’6” to a “space height” of 5’7.” Once back on Earth, though, gravity brings astronauts back down to their regular size.
Chicken legs, puffy faces and blurry vision
Without gravity, fluids shift. Because the body is 70% liquid, that change is felt at multiple levels.
On Earth, fluids in the body tend to shift downward, below the heart. But in space, fluids flow evenly throughout the body and shift into places they don’t normally accumulate.
It’s similar to doing a very long handstand: The 1½ gallons of liquid the body carries move upward. Astronauts often say they feel like they have a head cold and develop an issue that some at NASA call “puffy face syndrome,” “bird legs” or “chicken legs.” The problems typically clear up after about three days on Earth, according to NASA.
The fluid movement in the body may also cause lingering back problems, regardless of the length of the space flight. One study found that the incidence of a slipped or ruptured disc is 4.3 times higher in astronauts than in terrestrial populations, and the problem typically happens soon after they return to Earth.
The fluid redistribution issue also seems to affect many astronauts’ vision, a problem NASA has dubbed Spaceflight Associated Neuro-Ocular Syndrome. The eye flattens due to fluid redistribution, the retinal nerve fiber layer can thicken, and there is a refractive shift so the vision can blur in space.
Dr. Michael Harrison, an aerospace medicine specialist at Mayo Clinic in Florida, says it’s a bit like using a projector and moving it a few inches closer to the wall.
“The picture is going to get a little fuzzier,” he said. “It’s a major topic because we don’t know an awful lot about it yet.”
The problem seems to be more common with longer space flights.
“The question that is on everybody’s mind is, what happens when we go deeper into space for longer periods of time? Does it plateau, or is this something continues to progress?” Harrison said.
Not everyone’s vision remains changed. One study found globe flattening in about 16% of astronauts post-flight.
“Some folks come back and do have what appears to be – maybe not necessarily permanent changes but chronic changes in vision and requires glasses. Others don’t have it. It’s a fairly new phenomenon,” Harrison said.
To study the phenomenon, the crew of the five-day commercial flight Polaris Dawn wore special contact lenses last year to measure and collect data on the pressure in their eyes.
NASA has also developed special “space anticipation glasses” that are kept at the International Space Station. The glasses are adjustable and mitigate some of the blurriness.
Fluid in the brain tends to shift in space as well, from the top of the brain to the base. Studies of astronauts after they return to Earth have found that this shift can enlarge parts of their brains called ventricles, even beyond what can typically be seen with normal aging.
However, MRIs of the crew of the Polaris Dawn mission didn’t find any concerning findings with their brains.
Changes at the cellular level
Time in space can weaken a person’s immune system and make astronauts more susceptible to infections. The white blood cells that help the body fight infections seem to change.
“In space, there’s been activation of some latent viruses that folks carry but no health effects associated with that long-term,” Harrison said.
Space also seems to chemically modify a person’s DNA. On the International Space Station, astronauts wear dosimeters to record their radiation exposure, since it can damage DNA and raise the lifetime cancer risk
It’s not totally clear what effects other chemical changes to the DNA might have. A study that compared data during and after astronaut Scott Kelly’s mission to space against data from his identical twin brother, retired astronaut Mark Kelly, found that there were chemical modifications to both men’s DNA, but both returned to normal when they returned to Earth.
Telomeres, the repetitive sequences at the end of a chromosome that protect it from deteriorating, typically decrease with age, but Scott’s telomeres actually increased while he was in space. When he came back to Earth, they shortened again. Scientists say Scott’s telomeres may have been positively affected by his better exercise and diet routine in space.
Readjusting to Earth
Even before they come home, Williams and Wilmore will have increased their fluids using salt tablets and water to try to get back some of what they lost during the early phase of space flight, Dervay said. They also put on garments like compression socks that stretch from the feet to above the waist to move fluid back to the centers of their bodies.
“Every crew that comes back comes through a fluid loading protocol, just to make sure when they get back that their body is conditioned properly,” Steve Stitch, manager NASA’s commercial crew program, said Friday. “There’s nothing beyond what we’ll normally do.”
The astronauts do not return to their families right away after they splash down. Return-to-Earth protocols include keeping the crew at Johnson Space Center in Houston for several days before the flight surgeons give them the OK to go home.
“Almost every organ system in the body is impacted to some degree – whether it’s the skin, the neurovestibular, the bone, muscle, the immunological system, the cardiovascular system – so we have programs that our Human Health and Performance team focuses on to try and make sure that we’re covering all those areas,” Dervay said.
Scientists monitor all astronauts’ health from the time they start training until long after they retire, but as more people spend more days in space, researchers are gaining a much better understanding of what effect it can have on human health in the long term. It’s knowledge that will be essential as government and commercial space programs aim to send humans for extended stays on the Moon and Mars.
When astronauts return to Earth, their rehabilitation program may involve a series of physical exercises to increase bone density and strengthen muscles. They also do cardiovascular exercises to strengthen their heart muscle, since it doesn’t have to pump as hard in zero gravity as it does on Earth. Additionally, there are exercises to improve coordination to help prevent injuries.
“Gravity is really, really tough,” Wilmore told Cooper.
Williams said she usually gets her fast-twitch muscles back and her inner ear adjusts in about 24 to 48 hours after returning to Earth. She appreciates the quick physical improvements, but they’re also a little bittersweet.
“That will be a little bit sad when [the dizziness] goes away, just because that means that really, physically, the space flight came to an end,” she told Cooper.
For at least some astronauts, mental health may have the biggest effects. They often experience the “overview effect.”
“They get this profound experience that then influences their views on things when they return to Earth,” Harrison said.
Astronauts describe seeing the world from above as “beautiful” and “fragile.” It is a world without borders or boundaries, and seeing it causes some to feel an increased sense of connection to others.
“I’m not going to necessarily use the word ‘magical,’” Harrison said, “But it is a very profound philosophical experience being in space.”