By Will Dunham
WASHINGTON — A study of bone loss in 17 astronauts who flew aboard the International Space Station provides a fuller understanding of the effects of space travel on the human body and steps that can mitigate it, crucial knowledge ahead of potentially ambitious future missions.
The study provided new data on bone loss in astronauts caused by microgravity conditions in space and the extent to which bone mineral density can be restored 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 duration of about 5-1/2 months.
One year after returning to Earth, the astronauts showed an average of 2.1 percent decreased bone mineral density in the tibia—one of the lower leg bones—and 1.3 percent decreased bone strength. Nine did not regain bone mineral density after spaceflight, experiencing permanent loss.
“We know that astronauts lose bone during long space flights. What’s new about this study is that we followed the astronauts a year after their spaceflight to find out if and how the bones are repairing,” said University of Calgary professor Lee Gable, an exercise scientist who was the lead author of the study published this week. in the journal Scientific Reports.
“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 recovered only about half of that loss after a year back on Earth,” Gabel said.
Bone loss occurs because bones that would normally bear weight on Earth do not bear weight in space. Space agencies will need to improve countermeasures — exercise and nutrition regimens — to help prevent bone loss, Gabel said.
“During spaceflight, the fine 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 ligaments can thicken and strengthen, but those that have broken down in space cannot be repaired, so the astronaut’s overall bone structure is permanently altered,” Gabel said.
Astronauts from the study have flown on the space station for the past seven years. The study did not give their nationalities, but they are 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 as they plan new explorations. For example, NASA is aiming to send astronauts back to the moon, a mission now planned for 2025 at the earliest. This could be a prelude to future astronaut missions to Mars or a longer-term presence on the lunar surface.
“Microgravity affects many body systems, muscles and bones being among them,” Gabel said.
“The cardiovascular system also undergoes many changes. Without gravity pulling blood toward 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 concern for astronauts because the farther they travel from Earth, the greater the exposure to solar radiation and the increased risk of cancer,” Gabel said.
The study showed that longer space missions lead to both more 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 compared to what they would normally do on Earth were found to be more likely to rebuild 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 effects,” Gabel said. “We really hope that bone loss will eventually pick up on longer missions, that people will stop losing bone, but we don’t know.”
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