PARIS
Astronauts lose bone mass over decades in space, which many do not regain even after a year on Earth, researchers said June 30, warning that this could be a “major concern” for future missions to Mars.
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Previous research has shown that astronauts lose between one and two percent of bone density for each month spent in space, as the lack of gravity reduces the strain on their legs when it comes to standing up and walking.
To understand how astronauts recover after their feet are 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 over several decades if they returned to 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 the density of the tibia of nine of the astronauts had not fully recovered after a year on Earth, and they still lacked bone mass for about a decade.
Astronauts who went on the longest missions, which ranged from four to seven months on the ISS, recovered the slowest.
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“The longer you spend in space, the more bone you lose,” Boyd told AFP.
Boyd said this is a “big concern” for planned future missions to Mars, where astronauts could spend years in space.
“Will it continue to deteriorate over time or not? We don’t know,” he said.
“We may reach a steady state after a while, or we may continue to lose bone.” But I can’t imagine we’ll keep losing it until there’s nothing left.
A 2020 modeling study predicted that during a three-year spaceflight 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 that exists”.
“Even with two hours of exercise a day, it’s like being bedridden for the other 22 hours,” said the doctor, who was not part of the study.
“It won’t be easy for the crew to set foot on Martian soil when they arrive – it’s very debilitating.”
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