A new study has found that astronauts on space missions lasting more than six months suffer decades of bone loss, much of which could be irreversible. The finding could pose a serious challenge for future manned missions to Mars.
For missions that last six months or more, astronauts ’exposure to space microgravity causes them to experience bone loss equivalent to two decades of aging. And only half of the lost bone is recovered after a year on Earth, leaving them a decade old in their bone structure, the researchers wrote in a study published June 30 in the journal . Scientific reports (opens in a new tab).
Bones, like muscles, always grow, and have evolved to reshape themselves under the constant mechanical stress caused by the Earth. gravity. And, like muscles, if weight-bearing bones are not used, such as during a long, low-gravity stay in space, they can be irreversibly weakened.
Related: Why NASA’s new “Mega Moon rocket” is so amazing
“We found that weight-bearing bones were only partially recovered in most astronauts a year after space flight,” lead author Leigh Gabel, an assistant professor of kinesiology at the University of Calgary in Canada. he said in a statement. “This suggests that permanent bone loss due to spaceflight is roughly the same as a decade of age-related bone loss on Earth.”
The researchers evaluated the bones of 17 astronauts who had remained on the International Space Station (ISS). The astronauts, 14 men and three women, had an average age of 47 years. His stays on board the ISS ranged from four to seven months.
To track the deterioration and bone recovery of the astronauts, the researchers scanned specific regions of the astronauts’ bodies, such as the wrists, ankles and shins, before traveling to the ISS and as soon as they returned. The scientists then conducted two follow-up scans six and 12 months after the astronauts took a step back on solid ground.
The scans were done using a technique called high-resolution peripheral quantitative computed tomography (HR-pQCT), which creates 3D images of the human bone structure at scales thinner than the width of a human hair. With these scans, the researchers found out the astronauts’ bone mineral content and bone density, key indicators of how bones are susceptible to fracture.
The results showed that, of the 17 astronauts, 16 had not regained the strength of the tibia prior to space after a year of recovery. In addition, after the year of recovery, the eight astronauts who spent more than six months in space had tibia bones that had experienced the equivalent of a decade of aging and could withstand 75 pounds (334 Newtons). of far less than they could before their space missions. . In contrast, the bones of the lower arms (radii) of space travelers had barely deteriorated, probably because these bones could not support weight.
The bones can be roughly divided into two layers: the cortical and the trabecular. The cortical part of the bone represents approximately 80% of the human bone mass and is the outer axis of the bone that gives it shape. The remaining 20% of the bone mass is made up of the trabecular component, which is the lattice structure of microscopic beams and struts that reinforce the cortical bone from within. When people lose bone density, part of this trabecular hive disappears, reducing the strength of the bones and making them much more vulnerable to breakage.
“We have seen that many of these connections are lost during space flight, and so it is very likely that even if a new bone is formed when it returns to Earth, the body’s ability to replace the missing bars is very unlikely, ”Steven said. Boyd, a professor of radiology at Cumming School of Medicine in Calgary, Canada, told Live Science.
Previous research has predicted that during a three-year round trip to Mars, 33% of astronauts would return at risk of osteoporosis, a progressive condition that causes holes and spaces in the bone honeycomb. they grow, making them more likely to break.
And it’s not just the bone that deteriorates in low severity. Previous studies have also shown that muscles, eyes, brain, heart, spine and even cells can be damaged by prolonged stays in space, all of which present unique challenges for space flights. long lasting. The advantage of the new study is that the dead-flight training provided by the ISS’s Advanced Resistant Exercise Device (ARED) slowed the rate of bone loss and increased recovery, meaning that regimens of Specific training, equipment, and specific nutrition could be vital to keeping Astronauts fit together on long journeys, such as a future three-year round-trip mission to Mars.
“Since narrow spaces will be a limiting factor in future exploration class missions, exercise equipment will need to be optimized for a smaller footprint,” the scientists wrote in the study. “Training endurance exercises (especially deadlifts and other lower body exercises) will continue to be a mainstay in mitigating bone loss; however, adding a jump exercise to orbiting regimens can further prevent bone loss and reduce daily exercise time “.
Scientists are now planning a follow-up study to investigate the impacts that trips of more than seven months have on bones. This research is planned as part of a NASA project to study the long-term effects of space on more than a dozen vital parts of the human body.
“Those who spent more time in space lost more bones. So it would be reasonable to assume that spending even more time in space could mean more bone loss,” Boyd said. “This is obviously a concern for missions that can take years (e.g., Mars). But what we don’t know is whether the human body reaches a plateau of bone loss at some point. It doesn’t seem likely that the bones will.” it would melt “completely, but we don’t know at what level of balance of bone loss can be achieved.”
Beyond helping astronauts stay healthy during long flights, research also provides information on how to help them adapt to another shock to their systems: their return to Earth.
“Just as the body has to adapt to space flight at the beginning of a mission, it also has to readjust to the Earth’s gravitational field at the end,” said Robert Thirsk, a former rector and astronaut. of the University of Calgary, in the statement. “Fatigue, dizziness and imbalance were immediate challenges for me on my return. Bones and muscles take longer to recover after space flight. But after a day of landing, I left to feel comfortable again as an earthling. “
Originally published in Live Science.