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Here’s what should complicate manned missions to Mars

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According to a recent study, astronauts who spend more than six months in space suffer up to two decades of bone loss, much of which could be irreversible. This discovery could pose a serious challenge for future manned missions to Mars.

We are the product of millions of years of evolution shaped under the constant mechanical stress caused by Earth’s gravity. This is why prolonged stops in space put a strain on our body. Vestibular dysfunction, weight loss, muscle wasting or decreased red blood cell count, the list of known ailments today is very long. We have also known for several years that a prolonged stay in space can weaken the bones of astronauts. A study published in Science Advances shows us that the problem is more concerning than expected. Understanding and overcoming these challenges will, however, be essential if we want to establish ourselves on the Moon or Mars.

Bones ten years older

As part of this work, researchers from the University of Calgary (Canada) analyzed the bones of seventeen astronauts (fourteen men and three women) having remained aboard the ISS for four to seven months. The median age was 47.

The team focused on three particular bony regions: the wrists, ankles and shins. All these parts of the body were scanned (using high-resolution quantitative peripheral tomography) before their stay in space and on their return. The scientists then performed follow-up analyzes at six and twelve months. This data was used to determine each astronaut’s bone mineral content and bone density.

Result: The astronauts’ exposure to the microgravity of space would have caused them bone loss equivalent to two decades of aging. Of the seventeen astronauts, sixteen had not regained prespace shin strength after a year of recovery. On this sample, the shin bones of those who had spent more than six months in space (eight astronauts) had always suffered the equivalent of a decade of aging. In other words, the latter had only recovered half of their bone capacity a year after their return to Earth. In contrast, the astronauts’ forearm bones (spokes) had just weakened, probably because these bones carried hardly any weight.

European astronauts
ESA astronaut Thomas Pesquet photographed outside the ISS on 20 June. Credit: NASA

The importance of the exercises

The skeleton is made up of two types of bones. On the one hand there is the compact or cortical bone. Rigid and cylindrical, it forms the wall of the long bones. On the other hand, we find trabecular bone (or spongy) which consists of loose and irregular spans. It makes up about 1/5 of the bone mass and strengthens the cortical bone from the inside. When we lose bone density, some of this “honeycomb” disappears. This has the effect of reducing the strength of the bones which in fact become more vulnerable to breaking. That’s what happened here with the astronauts.

We have seen that many of these connections are lost during space flight. And even if new bones are formed upon return to Earth, the body’s ability to completely replace those missing rods is highly unlikely.“, Underline the authors.

Also according to the researchers, the ARED gymnastic device, present on board the ISS since 2009 for resistance exercises in zero gravity, would have allowed slow down the rate of bone loss. This means that specific training regimes will be key to mitigating bone loss in long-duration space missions.

Scientists are now planning a follow-up study to assess the impact of the trip from more than seven months on the bones. Those who spent more time in space lost more bone, so we could imagine spending even more time in space could lead to additional bone loss. However, the researchers would like to know if the human body could reach a bone loss limit at some point.

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