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Lost in space: Astronauts struggle to regain bone density

Previous studies have shown that astronauts lose one to two percent of their bone density each month spent in space, because the lack of gravitational force in standing and walking reduces the pressure on their legs.

Astronauts have lost decades of valuable bone mass in space that could not be restored to Earth even a year ago, researchers said Thursday, which could be a “major concern” for future missions to Mars.

Previous studies have shown that astronauts lose one to two percent of their bone density each month spent in space, because the lack of gravitational force in standing and walking reduces the pressure on their legs.

To find out how astronauts recover when their feet return to the ground, a new study scanned the wrists and ankles of 17 astronauts before, during and after their stay on the International Space Station.

Steven Boyd, co-author of the study at the University of Calgary in Canada, and director of the McCage Institute for Sister and Joint Health, said the loss of bone density that astronauts lost was equivalent to how much they could actually lose within decades.

Researchers have found that the shinbone density of nine astronauts did not fully recover on Earth a year later – and still lacked bone mass worth nearly a decade.

The astronauts who went on the longest mission in the ISS for four to seven months were the slowest to recover.

“The more time you spend in space, the more bones you lose,” Boyd told AFP.

Boyd said it was a “big concern” to plan for future missions to Mars, which could see astronauts spend years in space.

“Is it going to get worse over time? We don’t know,” he said.

“It’s possible that we hit a steady state after a while, or it’s possible that we keep losing bone. But I can’t imagine that we’ll keep losing it until there’s something left.”

A 2020 modeling study predicts that on a three-year spaceflight to Mars, 33 percent of astronauts will be at risk of osteoporosis.

Boyd says some answers can be found from research that is currently being done on astronauts who have spent at least a year on the ISS.

Guillett Gaukelin-Koch, head of medical research at France’s CNES space agency, said the weightlessness felt in space was “the most severe physical inactivity out there.”

“Even with two hours of sports a day, it’s like you’re going to bed another 22 hours,” said the doctor, who was not part of the study.

“It won’t be easy for the crew to set foot on Mars when they arrive – it’s very inefficient.”

‘Silent Disease’

New research, published in the scientific report, also shows how spacecraft change bone structure.

Boyd said that if you think of the bones of the body like the Eiffel Tower, it would seem that some of the connecting metal rods that hold the structure are missing.

“And when we get back to Earth, we condense what’s left, but we don’t actually make new rods,” he said.

Some exercises are better than others for maintaining bone mass, studies have shown.

While deadlifting has proven to be significantly more effective than running or cycling, it suggests heavier lower-body exercises in the future.

But astronauts – most of whom are fit and did not have a tendency to notice severe bone loss between the ages of 40 and 40, Boyd said, are earth-bound equivalent osteoporosis known as “silent disease.”

Canadian astronaut Robert Thursk, who has spent the most time in space, says it takes him the longest time to recover bones and muscles after spacecraft.

“But within a day of landing, I felt as comfortable as Earthling again,” he said in a statement with the study.




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