A study of bone loss in 17 astronauts flying aboard the International Space Station provides a better understanding of the effects of space travel on the human body and the steps it can take to reduce it during potentially ambitious future missions.
Most important points:
- The study found that astronauts experienced significant bone loss during six-month flights
- The bone loss was comparable to what older adults on Earth would experience over two decades
- The astronauts only recovered about half of that loss after a year back on Earth
The research has collected new data on astronaut bone loss caused by microgravity in space and the ability to restore bone mineral density on Earth.
It involved 14 male and three female astronauts with an average age of 47 years, whose missions ranged from four to seven months in space, averaging about 5.5 months.
One year after their return to Earth, the astronauts showed an average of 2.1 percent decreased bone mineral density at the tibia – one of the bones of the lower leg – and 1.3 percent decreased bone strength.
Nine did not recover bone mineral density after spaceflight and experienced permanent loss.
“We know that astronauts lose bone during prolonged spaceflight. 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,” said University of Calgary professor of exercise science. who was the lead author of the study published this week in the journal Scientific Reports.
The bone loss occurs because bones that would normally be heavy on Earth do not carry any weight in space.
Space agencies will need to improve countermeasures — exercise regimens and nutrition — to help prevent bone loss, Professor Gabel said.
“During spaceflights, fine bone structures get thinner and eventually some bone rods come apart,” she said.
“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’s astronauts flew on the space station for the past seven years.
The study did not give their nationalities, but they were from the US space agency NASA, Canadian Space Agency, European Space Agency and Japan Aerospace Exploration Agency.
Space travel presents the human body with several challenges – major concerns for space organizations when planning new explorations.
For example, NASA is aiming to send astronauts back to the moon, a mission now slated for 2025 at the earliest.
That could be a prelude to future astronaut missions to Mars or a longer-term presence on the lunar surface.
“Microgravity affects many body systems, including muscles and bones,” said Dr. Gabel.
“The cardiovascular system also experiences many changes. Without gravity drawing blood to our feet, astronauts experience a fluid shift that causes more blood to collect in the upper body. This can affect the cardiovascular system and vision.
“Radiation is also a major health risk for astronauts because the farther they get from Earth, the greater the exposure to the sun’s radiation and the greater the risk of cancer.”
The study found that longer space missions resulted in both more bone loss and less chance of bone repair afterwards.
In-flight exercise — resistance training on the space station — proved important to prevent 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.
“There’s still a lot we don’t know about the impact of microgravity on human health, particularly in space missions longer than six months, and about the long-term health implications,” said Dr. gabel.
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