Paris (AFP) – Astronauts are losing bone mass in decades that many do not recover even after a year back to Earth, researchers said on Thursday, warning that it could be a “major concern” for future missions to Mars.
Previous research has shown that astronauts lose one to two percent of their bone density for each month they spend in space, as weightlessness removes pressure from their legs when they are about to stand and walk. To find out how astronauts recover when their feet are back on the ground, a new study has scanned the wrists and ankles of 17 astronauts before, during and after their stay on the International Space Station. The bone density lost by the astronauts was equivalent to how much they would throw in several decades if they returned to Earth, said study co-author Steven Boyd of the University of Calgary in Canada and director of the McCaig Institute for Health of the joints. The researchers found that the tibial density of nine of the astronauts had not fully recovered after a year on Earth – and they still lacked bone mass for about a decade. The astronauts who went on the largest missions, which ranged from four to seven months on the ISS, were the slowest to recover. “The more you spend in space, the more bone you lose,” Boyd told AFP. Boyd said there was “great concern” about planned future missions to Mars, which could see astronauts spend years in space. “Will it continue to get worse over time or not? We do not know,” he said. “It is possible that we will be in a stable state after a while, or it is possible that we will continue to lose bone. But I can not imagine that we will continue to lose it until there is nothing left.” A 2020 modeling study predicted that during a three-year space flight to Mars, 33 percent of astronauts would be at risk for osteoporosis. Boyd said some of the answers could come from research currently underway on astronauts who have spent at least a year on the ISS. Guillemette Gauquelin-Koch, head of medical research at the French space agency CNES, said the lack of gravity experienced in space was “the most drastic physical inactivity there is”. “Even with two hours of exercise a day, it’s like being in bed for the other 22 hours,” said the doctor, who did not take part in the study. “It will not be easy for the crew to set foot on the ground of Mars when they arrive – it is very disabled.”
“The silent disease”
The new study, published in Scientific Reports, also showed how spaceflight changes the structure of the bones themselves. Boyd said that if you thought about the bones of a body like the Eiffel Tower, it would be as if some of the connecting metal rods that hold the structure up were lost. “And when we go back to Earth, we thicken what’s left, but we’re not really creating new rods,” he said. Some exercises are better for maintaining bone mass than others, according to the study. Deadlifting has proven to be significantly more effective than running or cycling, he said, suggesting more heavy lower body exercises in the future. But astronauts – mostly in their 40s – did not tend to notice drastic bone loss, Boyd said, noting that Earth-equivalent osteoporosis is known as “silent disease.” Canadian astronaut Robert Tirsk, who has spent most of his time in space, said he needed the bones and muscles to recover the most after a space flight. “But within a day of landing, I felt comfortable again as an Earthling,” he said in a statement accompanying the search. © 2022 AFP
