Astronauts lose decades of bone mass in space, which many don’t recover even after a year on Earth, researchers said Thursday, warning it could be a “big problem” for future missions to Mars.
Previous research has shown that astronauts lose between 1 and 2 percent of bone density for each month they spend in space as the lack of gravity takes the strain off their legs when standing and walking.
To find out how astronauts recover once they’re back on the ground, a new study scanned the wrists and ankles of 17 astronauts before, during and after a stay on the International Space Station.
The bone density lost by astronauts is equivalent to the amount they would lose in several decades if they were back on Earth, said study co-author Steven Boyd of Canada’s University of Calgary and director of the McCaig Institute for Bone and Joint Health.
The researchers found that after a year on Earth, nine of the astronauts still had not fully recovered their tibia density – and they still lacked the bone mass of around a decade.
The astronauts on the longest missions, lasting between four and seven months on the ISS, recovered the slowest.
“The longer you’re in space, the more bones you lose,” Boyd told AFP.
Boyd said it’s a “big concern” for planned future missions to Mars, which could see astronauts spending years in space.
“Will it continue to get worse over time or not? We don’t know,” he said.
“It’s possible that after a while we’ll reach a stable state, or it’s possible that we’ll continue to lose bone. But I can’t imagine we’ll keep losing bones until there’s nothing left.”
A 2020 model study predicted that on a three-year space flight to Mars, 33 percent of astronauts would be at risk of osteoporosis.
Boyd said some answers may come from research currently being conducted on astronauts who have spent at least a year aboard the ISS.
Guillemette Gauquelin-Koch, head of medical research at the French space agency CNES, said the weightlessness experienced in space was “the most drastic physical inactivity there is”.
“Even if you exercise for two hours a day, you’re like bedridden for the remaining 22 hours,” says the doctor, who was not involved in the study.
“It won’t be easy for the crew to set foot on Martian soil when they arrive – it’s very debilitating.”
“The Silent Disease”
The new study, published in Scientific Reportsalso showed how space travel changes the structure of the bones themselves.
Boyd said if you think of the bones of a body like the Eiffel Tower, it’s as if some of the connecting metal rods that hold the structure were lost.
“And when we return to Earth, we thicken what’s left, but we don’t create new rods,” he said.
Some exercises are better for maintaining bone mass than others, the study found.
Deadlifts proved significantly more effective than running or cycling, it said, and suggested doing more heavy lower-body exercises in the future.
But the astronauts — who are mostly fit and in their 40s — didn’t notice the drastic bone loss, Boyd said, pointing out that the Earth-bound equivalent of osteoporosis is known as “the silent disease.”
Canadian astronaut Robert Thirsk, who has spent the most time in space, said his bones and muscles took the longest to recover after space flight.
“But within a day of landing, I felt comfortable as an earthling again,” he said in a statement accompanying the research.
© Agence France-Presse