最新研究表明太空旅行会造成永久性骨流失

A recent study about bone loss in astronauts is providing important information about the effects of space travel on the human body.

The research could help space agencies reduce harmful effects on astronauts in future space flights.

The recent research gathered new data on bone loss in 17 astronauts who worked on the International Space station.

It involved 14 male and three female astronauts. Their average age was 47 years old.

The study looked at bone loss caused by the microgravity conditions, or very weak force of gravity, in space. It also studied how bone mineral density can be regained back on Earth.

The astronaut's missions were about five and one half months on average.

One year after returning to Earth, the astronauts had 2.1 percent reduced bone mineral density at the tibia, a bone in the leg. They also had on average a 1.3 percent reduction in strength. Nine experienced permanent loss - they did not fully recover bone mineral density after the space flight.

Leigh Gabel of the University of Calgary was the lead writer of the research published recently in Scientific Reports.

Gabel said that what is new about this study "is that we followed astronauts for one year after their space travel to understand if and how bone recovers."

Gable noted that astronauts experienced bone loss during six-month spaceflights that one would expect to see in older people over 20 years on Earth.

These astronauts "only recovered about half of that loss after one year back on Earth," she added.

The bone loss happens because bones that usually carry weight on Earth do not carry weight in space. Space agencies are going to need to make better exercise and eating plans to help prevent bone loss, Gabel explained.

She noted that "During spaceflight, fine bone structures thin, and eventually some of the bone rods disconnect from one another."

The result, Gabel said, is that "once the astronaut comes back to Earth, the remaining bone connections can thicken and strengthen, but the ones that disconnected in space can't be rebuilt, so the astronaut's overall bone structure permanently changes."

The study's astronauts flew on the space station in the past seven years. The astronauts were from the U.S. space agency NASA, Canadian Space Agency, European Space Agency and Japan Aerospace Exploration Agency.

The effects of space travel on the human body are important for space agencies as they plan new explorations.

NASA is aiming to send astronauts back to the moon, a mission now planned for 2025 at the earliest. Future astronaut missions to Mars or a long-term presence on the Moon's surface are also possibilities.

Gabel said that muscle loss, bone loss, effects on the cardiovascular system, and even radiation are big concerns for astronauts.

"Without gravity pulling blood towards our feet, astronauts experience a fluid shift that causes more blood to pool in the upper body. This can affect the cardiovascular system and vision," Gabel explained.

She added that "Radiation is also a large health concern for astronauts as the further they travel from Earth the greater exposure to the sun's radiation and increased cancer risk."

The study showed that longer space missions resulted both in more bone loss and a lower likelihood of recovering bone later. In-flight exercise, such as resistance training, proved important for preventing muscle and bone loss. Astronauts who performed more deadlifts compared to what they usually did on Earth were found to be more likely to recover bone after the mission.

Gabel said there is still much to be learned about the effects of space travel on human health – particularly on space missions longer than six months.

I'm John Russell.

Will Dunham reported on this story for Reuters. John Russell adapted it for VOA Learning English.

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microgravity – n. very weak gravity

mission –n. a flight by an aircraft or spacecraft to perform a specific task

cardiovascular system – n. of or relating to the heart and blood vessel system of the body

deadlift – n. a lift in which the weight is lifted from the floor