The research gathered new data on bone loss in astronauts caused by the microgravity conditions of space and the extent to which bone density can be recovered on Earth. It involved 14 male and three female astronauts, with an average age of 47, whose missions ranged from four to seven months in space, with an average of about 5 1/2 months.
One year after returning to Earth, the astronauts showed an average of 2.1% decreased bone density in the tibia – one of the lower leg bones – and 1.3% decreased bone strength. Nine did not regain bone density after spaceflight, facing permanent bone loss.
“We know that astronauts lose bone on long-duration spaceflights. What’s new about this study is that we followed the astronauts for a year after their spaceflight to understand if and how the bones recover,” said the University professor of Calgary, Leigh Gabel, exercise scientist. who was the lead author of the research published this week in the journal Scientific Reports.
A view of the astronauts’ uniform room, in the Astronaut Crew Quarters (ACQ) in the Neil Armstrong Checkout and Operations Building at the Kennedy Space Center, Cape Canaveral, Florida, US, June 14, 2022. (AFP Photo)
“Astronauts experienced significant bone loss during six-month spaceflights — loss that we would expect to see in older adults over two decades on Earth, and recovered only about half of that loss after a year back on Earth,” said Gabel.
Bone loss occurs because bones that would normally be weight-bearing on Earth are not weight-bearing in space. Space agencies will need to improve countermeasures — exercise regimens and diet — to help prevent bone loss, Gabel said.
“During spaceflight, the delicate bone structures become thinner, and eventually some of the bone rods become disconnected from each other. Once the astronaut returns to Earth, the remaining bone connections may thicken and strengthen, but those that were disconnected in in space they cannot be rebuilt, so the overall bone structure of the astronaut is permanently changed,” Gabel said.
Astronauts in the study have flown to the space station for the past seven years. The study did not give their nationalities, but they were from the United States space agency NASA, the Canadian Space Agency, the European Space Agency and the Japan Aerospace Exploration Agency.
An “astronauts only” sign is displayed at the Astronaut Crew Quarters (ACQ) in the Neil Armstrong Operations and Checkout building at the Kennedy Space Center, Cape Canaveral, Florida, US, June 14, 2022. (AFP Photo)
Space travel poses various challenges to the human body – key concerns for space agencies as they plan new explorations. For example, NASA aims to send astronauts back to the Moon, a mission planned for 2025 at the earliest. This could be a prelude to future astronaut missions to Mars or a long-term presence on the lunar surface.
“Microgravity affects many body systems, including those muscles and bones,” Gabel said.
“The cardiovascular system also undergoes many changes. Without gravity pulling blood to our legs, astronauts experience a fluid shift that causes more blood to pool in the upper body. This can affect the cardiovascular system and vision.
“Radiation is also a big health problem for astronauts, as the farther they travel from Earth the greater the exposure to solar radiation and the increased risk of cancer,” Gabel explained.
The study showed that longer space missions resulted in both greater bone loss and a lower chance of bone recovery afterwards. Inflight exercise – resistance training on the space station – has been shown to be important in preventing muscle and bone loss. Astronauts who did more deadlifts compared to what they would normally do on Earth were found to be more likely to recover their bones after the mission.
“There is a lot we still don’t know about how microgravity affects human health, particularly on space missions longer than six months, and about the long-term health consequences,” Gabel said. “We really hope that bone loss will eventually plateau in longer missions, that people will stop losing bone, but we don’t know,” he cautioned.
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