An academic-led study of astronauts has revealed the devastating impact space travel has on the human skeleton.
The research showed that astronauts suffered “significant” bone loss during six-month spaceflights — equivalent to about two decades on Earth.
Only about half of the bone loss was recovered a year after return, raising concerns about future missions to Mars and the moon.
Longer space missions led to more bone loss and a reduced chance of recovery.
The bone loss occurs due to a lack of gravity in space, where normally weight-bearing bones on Earth are weightless.
The study was conducted on 17 astronauts – 14 men and three women with an average age of 47 years – who were aboard the International Space Station (ISS) in the past seven years.
The crew came from the US space agency NASAthe Canadian and European space agencies and the Japanese Space Agency.
They spent a year working with a research team led by Leigh Gabel, a professor at the University of Calgary, after they returned to Earth.
Nine crew members experienced permanent loss of bone mineral density after spending four to seven months on space missions.
“Astronauts experienced significant bone loss during six months of spaceflight — loss we would expect in older adults over two decades on Earth, and they only recovered about half of that loss after a year back on Earth,” said Professor Gabel of the study, published in the journal Scientific Reports.
“We know that astronauts lose bone during prolonged spaceflights.
“What’s new about this study is that we followed astronauts for a year after their space journey to understand if and how bone recovers.”
Space agencies need to improve countermeasures, such as exercise and diet, to prevent bone loss, Professor Gabel warned.
In-flight exercises, including resistance training on the ISS, were found to be crucial for preventing bone and muscle loss, the study found.
Astronauts who completed more deadlift weights compared to their usual training routine on Earth were more likely to recover bone after a mission.
The astronauts lost an average of 2.1% decreased density in the lower leg, tibia and 1.3% decreased bone strength.
“During spaceflights, fine bone structures become thinner and eventually some bone rods become disconnected from each other,” said Professor Gabel.
“Once the astronaut returns to Earth, the remaining bone connections can get thicker and stronger, but those disconnected in space cannot be rebuilt, so the astronaut’s overall bone structure changes permanently.”
The study also found that the cardiovascular system is also affected by space travel.
“Without the gravity pulling 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.”
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Radiation is also a concern, as astronauts are more exposed to the sun and have an increased risk of cancer the further they are from Earth.
Professor Gabel added: “There is still a lot we don’t know about the impact of microgravity on human health, especially in space missions longer than six months, and about the long-term health implications.
“We really hope that the bone loss eventually stops during longer missions, that people stop losing bone, but we don’t know.”
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