An academically led study by astronauts has revealed the devastating impact space travel has on the human skeleton.
The research showed that astronauts suffered from “significant” bone loss during six-month spaceflights – equivalent to about two decades on Earth.
Only about half of the bone loss was found a year after returning home – which raised concerns about future missions to Mars and the moon.
Longer space missions led to increased bone loss and reduced likelihood of recovery.
Bone loss occurs due to lack of gravity in space, where weight-bearing bones on Earth are weightless.
The study was conducted on 17 astronauts – 14 men and three women with a mean age of 47 – who flew on board International Space Station (ISS) for the past seven years.
The crew came from the US space agency NASAthe Canadian and European space agencies and the Japanese Space Agency.
They worked with a research group led by Professor Leigh Gabel at the University of Calgary, for a year after returning to Earth.
Nine crew members experienced permanent bone density after spending between four and seven months on space missions.
“Astronauts experienced significant bone loss during six-month spaceflights – a loss we would expect to see in older adults over two decades on Earth, and they recovered only about half of that loss after a year back on Earth,” Professor Gabel said of research, published in the journal Scientific Reports.
“We know that astronauts lose bones during long space travel.
“The new thing about this study is that we followed astronauts for a year after their spaceflight to understand if and how bones recover.”
Space organizations must improve countermeasures, such as exercise and nutrition, in an effort to prevent bone loss, Professor Gabel warned.
In-flight training including resistance training on the ISS proved to be crucial in preventing bone and muscle loss, the study found.
Astronauts who managed more ground lifting weights compared to their usual training routine on earth were more likely to recover legs after a mission.
The astronauts lost an average of 2.1% reduced density in the bone, tibia and 1.3% reduced bone strength.
“During space travel, fine bone structures become thin, and eventually some of the bone rods become disconnected,” said Professor Gabel.
“Once the astronaut returns to Earth, the remaining bone connections may thicken and strengthen, but those disconnected in space cannot be rebuilt, so the astronaut’s overall bone structure changes permanently.”
The research also found that the cardiovascular system is also affected by space travel.
“Without gravity drawing blood to our feet, astronauts experience a fluid shift that causes more blood to collect in the upper body,” said Professor Gabel. “This can affect the cardiovascular system and vision.”
Radiation is also a problem, with astronauts facing greater exposure to the sun and an increased risk of cancer the farther they travel from Earth.
Professor Gabel added: “There is much we still do not know about how microgravity affects human health, especially in space missions longer than six months, and about the long-term health consequences.
“We really hope that bone loss will eventually plateau on longer missions, that people will stop losing bones, but we do not know.”
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