A study of bone loss in 17 astronauts who flew aboard the International Space Station is increasing understanding of the effects of space travel on the human body and measures that can mitigate them, crucial knowledge before potential ambitious missions.
The research has accumulated new data on bone loss in astronauts caused by the microgravity conditions of space and the degree to which bone mineral density can be regained on Earth. It involved 14 male and three female astronauts, with an average age of 47 years, whose missions ranged from four to seven months in space, with an average of about five and a half months.
One year after returning to Earth, the astronauts exhibited, on average, a 2.1% reduction in bone mineral density in the tibia—one of the bones in the leg—and a 1.3% reduction in bone strength. Nine did not regain bone mineral density after spaceflight and had permanent loss.
“We know that astronauts experience bone loss on long-duration spaceflights. The novelty of this study is that we followed astronauts for a year after their spaceflight to understand if and how bone heals,” said Leigh Gabel, a professor at the University of Calgary, an exercise scientist who was the lead author of the research published this week in the journal Scientific Reports.
“Astronauts experienced significant bone loss during their six-month spaceflights — loss that we would expect to see in older adults over two decades on Earth, and they only recovered about half of that loss after a year back on Earth.” said Gabel.
Bone loss occurs because bones that would normally bear weight on Earth do not carry weight in space. Space agencies will need to improve compensatory measures — exercise and nutrition regimens — to help prevent bone loss, Gabel said.
“During spaceflight, bone structures thin out. Once the astronaut returns to Earth, the remaining bone connections can thicken and strengthen, but the ones that became disconnected in space cannot be reconstructed, so the astronaut’s overall bone structure changes permanently,” said Gabel.
The astronauts in the study have flown on the space station for the past seven years. The study does not disclose their nationalities, but they were from NASA, the Canadian Space Agency, the European Space Agency and the Japan Aerospace Exploration Agency.
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