A study of bone loss in 17 astronauts who flew aboard the International Space Station provides insight into the effects of space travel on the human body and the steps that can mitigate them, crucial knowledge ahead of potential future ambitious missions.
Research has amassed new data on bone loss in astronauts caused by the microgravity conditions of space and the extent to which bone mineral density can be traced back to Earth. It involved 14 male and three female astronauts, with an average age of 47, whose missions lasted four to seven months in space, with an average of around 5.5 months.
A year after returning to Earth, the astronauts had an average of 2.1% reduced bone mineral density in the tibia – one of the lower leg bones – and 1.3% reduced bone strength. Nine did not regain their bone mineral density after spaceflight, suffering permanent loss.
“We know that astronauts lose bone during long-duration spaceflight. What’s new about this study is that we followed the astronauts for a year after their space journey to understand if and how the bones recover,” said Leigh Gabel, a University of Calgary professor and exercise expert. who was the lead author of the research published this week in the journal Scientific Reports https://www.nature.com/articles/s41598-022-13461-1.
“Astronauts suffered significant bone loss during six-month spaceflights – a loss we would expect to see in older people over two decades on Earth, and they only recovered about half of that loss. after a year back on Earth,” Gabel said.
Bone loss occurs because bones that would generally be weight-bearing on Earth are not weight-bearing in space. Space agencies are going to have to improve countermeasures — exercise regimens and nutrition — to help prevent bone loss, Gabel said.
“During spaceflight, the fine bony structures become thinner and some of the bony rods eventually become disconnected from each other. Once the astronaut returns to Earth, the remaining bony connections may thicken and strengthen, but those that disconnected in space cannot be rebuilt, so the astronaut’s overall bone structure changes permanently,” Gabel said.
The astronauts in the study have flown on the space station for the past seven years. The study did not give their nationalities but they were from the US space agency NASA, the Canadian Space Agency, the European Space Agency and the Japan Aerospace Exploration Agency.
Space travel poses various challenges to the human body – major concerns for space agencies when planning new explorations. For example, NASA aims to return astronauts to the Moon, a mission now scheduled for 2025 at the earliest. It could be a prelude to future astronaut missions to Mars or a longer-term presence on the lunar surface.
“Microgravity affects many bodily systems, including muscles and bones,” Gabel said.
“The cardiovascular system also undergoes many changes. Without gravity drawing blood to our feet, astronauts experience a fluid change that causes blood to pool in the upper body. This can affect the cardiovascular system and vision.
“Radiation is also a big health concern for astronauts because the further they get from Earth, the more they are exposed to solar radiation and increases the risk of cancer,” Gabel said.
The study showed that longer space missions resulted in both greater bone loss and a lower likelihood of bone recovery afterwards. In-flight exercise – resistance training on the space station – has been shown to be important in preventing muscle and bone loss. Astronauts who performed more deadlifts than they usually did on Earth were found to be more likely to recover bones after the mission.
“There’s a lot we still don’t know about how microgravity affects human health, especially on space missions longer than six months, and the long-term health consequences,” Gabel said. “We really hope that bone loss will eventually stabilize on longer missions, that people will stop losing bone, but we don’t know.”
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