Astronauts lose decades of bone mass in space, which many may not regain even after a year on Earth, according to experts, who warn that it might be a "big concern" for future Mars missions.
Previous study has found that astronauts lose 1 to 2 percent of their bone density for every month spent in space, since the lack of gravity relieves strain on their legs when standing and walking.
A new research examined the wrists and ankles of 17 astronauts before, during, and after their stay on the International Space Station to see how they recuperate once their feet are back on the ground.
According to research co-author Steven Boyd of Canada's University of Calgary and head of the McCaig Institute for Bone and Joint Health, the bone density lost by astronauts was similar to how much they would lose in several decades if they were back on Earth.
The researchers discovered that nine of the astronauts' shinbone density had not entirely recovered after a year on Earth, and they were still missing about a decade's worth of bone mass.
The astronauts who spent the most time on the ISS, ranging from four to seven months, recovered the slowest.
"The longer you spend in space, the more bone you lose," according to Boyd.
Boyd described it as a "big concern" for future Mars missions, which may see people spend years in orbit.
"Will it continue to get worse over time or not? We don't know," he stated.
"It's possible we hit a steady state after a while, or it's possible that we continue to lose bone. But I can't imagine that we'd continue to lose it until there's nothing left."
According to a 2020 modeling research, 33 percent of astronauts would be at danger of osteoporosis during a three-year trip to Mars.
Some answers, according to Boyd, might come from existing studies on astronauts who have spent at least a year on the International Space Station.
According to Guillemette Gauquelin-Koch, chief of medical research at France's CNES space agency, weightlessness in space is the "most drastic physical inactivity there is".
"Even with two hours of sport a day, it is like you are bedridden for the other 22 hours," said a doctor who was not involved in the study.
"It will not be easy for the crew to set foot on Martian soil when they arrive – it's very disabling."
'The silent disease'
The latest study, published in Scientific Reports, also demonstrated how spaceflight affects the structure of bones.
Boyd stated that if a body's bones were compared to the Eiffel Tower, it would be as if part of the connecting metal rods that keep the tower up were gone.
"And when we return to Earth, we thicken up what's remaining, but we don't actually create new rods," he said.
The study discovered that some workouts are better than others for preserving bone mass.
According to the study, deadlifting was substantially more beneficial than jogging or cycling, indicating that more heavier lower-body activities should be performed in the future.
However, the astronauts, who are mainly athletic and in their 40s, did not detect the severe bone loss, according to Boyd, noting that the Earth-bound counterpart osteoporosis is known as "the silent disease."
Canadian astronaut Robert Thirsk, who has spent the most time in space, stated that following spaceflight, his bones and muscles required the longest to recuperate.
"But within a day of landing, I felt comfortable again as an Earthling," he added in a statement accompanying the study.
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