Astronauts lose decades of bone mass in space that many do not regain even after a year back on Earth, researchers said June 30, 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 bone density for each month they spend in space, as the weightlessness takes the pressure off their legs when it comes to standing and walking. To find out how astronauts recover when their feet are back on the ground, a new study scanned the wrists and ankles of 17 astronauts before, during and after their stay on the International Space Station. The bone density the astronauts lost was equivalent to how much they would lose over several decades if they returned to Earth, said study co-author Stephen Boyd of the University of Calgary in Canada and director of the McCaig Institute for Bone Health and of the joints. The researchers found that the bone density of nine of the astronauts had not fully recovered after a year on Earth, and they still lacked about a decade’s worth of bone mass. Astronauts who went on the longest missions, which ranged from four to seven months on the ISS, were the slowest to recover.
“The longer you spend in space, the more bone you lose,” Boyd told AFP. Boyd said it is a “big concern” for planned future 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’ll be in a steady state after a while, or it’s possible that we’ll continue to lose bone. But I can’t imagine we’re going to 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 could come from research currently being conducted 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 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 involved in the study. “It won’t be easy for the crew to set foot on Martian soil when they arrive – it’s too crippling.”
