Lost in space: Returning astronauts struggle to regain bone density, study finds | Space

Astronauts lose decades of bone mass in space that many don’t regain even after a year back on Earth, researchers have found, warning it could be a “big concern” for future missions to Mars.

Previous research has shown that astronauts lose between 1% and 2% of their bone density for each month spent in space, as the absence of gravity relieves their legs when it comes to standing and walking. .

To find out how astronauts recover once their feet are 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 (ISS).

The bone density lost by astronauts is equivalent to what they would lose in decades if they were back on Earth, said study co-author Dr Steven Boyd, from Canada’s University of Calgary and director of the McCaig Institute for Bone and Joint Health.

The researchers found that the tibia density of nine of the astronauts had not fully recovered after a year on Earth – and they were still around a decade short of bone mass.

The astronauts who flew the longest missions, which lasted four to seven months on the ISS, were the slowest to recover. “The more time you spend in space, the more bones you lose,” Boyd said.

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

“Will it continue to get worse over time or not? We don’t know,” he said.

“It’s possible that we reach a stable state after a while, or it’s possible that we continue to lose bone. But I can’t imagine we would keep losing it until there’s nothing left.

A 2020 modeling study predicted that during a three-year spaceflight to Mars, 33% of astronauts would be at risk for 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 is “the most drastic physical inactivity there is”.

“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 will not be easy for the crew to set foot on Martian soil when they arrive, it is very disabling.”

The new study, which was published in Scientific Reports, also showed how spaceflight changes the structure of the bones themselves.

Boyd said if you thought of the bones in a body like the Eiffel Tower, it would be as if some of the connecting metal rods that hold the structure together were lost. “And when we go back to Earth, we thicken up what’s left, but we don’t actually create new stems,” he said.

Some exercises are better at retaining bone mass than others, according to the study. The deadlift was found to be significantly more effective than running or cycling, he said, suggesting heavier lower-body exercises in the future.

But the astronauts — who were mostly fit and in their 40s — didn’t tend to notice the drastic bone loss, Boyd said, pointing out that Earth’s equivalent, osteoporosis, is known as ” silent disease”.

Canadian astronaut Robert Thirsk, who has spent the longest time in space, said his bones and muscles take the longest to recover after spaceflight.

“But a day after landing, I felt comfortable again as an earthling,” he said in a statement accompanying the search.