(Paris) Loss of bone mass, heart problems, kidney stones… The human body is put to the test in space, but it recovers almost entirely three months after returning to Earth, conclude around twenty studies carried out on tourists space, published Tuesday in Nature.

“This is the most in-depth examination we have ever conducted on a crew,” explained Christopher Mason of Weill Cornell Medicine in New York, lead author of one of the studies, at a press conference.  

Understanding the health impacts of spaceflight is crucial for future manned lunar missions and beyond, but also for the space tourism industry, which hopes to send into orbit everyone who can afford it.

Researchers from more than 100 institutions around the world sifted through data on the health of four Space X space tourists, who spent three days in orbit without any professional astronauts on board, in September 2021 .   

The sample size is small compared to the nearly 700 people who have already visited space since the start of the conquest of space. But governments haven’t always been willing to share data from their missions, pointed out NASA’s Afshin Beheshti, one of the scientists who conducted the research.

The four Americans from the Inspiration4 mission did not hesitate to submit to a battery of examinations. The results were widely disseminated and compared to the results of tests conducted on 64 other astronauts.

Changes in the blood, heart, skin, proteins, kidneys, genes, cells: nothing or almost nothing about the body has been forgotten.  

Human spaceflight can cause bone loss, heart problems, eye problems, kidney problems and more. But about 95 percent of these health markers return to their previous levels within three months of returning to Earth, and people recover quickly, says Mason.

The scientist hopes these findings will help scientists identify which drugs or measures will be needed to better protect crews.  

The Inspiration4 mission, funded by its billionaire captain Jared Isaacman, wanted to demonstrate that space is accessible to people who have not spent years training for this feat.  

One of the studies revealed that the telomeres –– the ends of chromosomes – of the four crew members had elongated dramatically in orbit. But in the months since they returned to Earth, they have returned to their original length.  

Since telomeres also lengthen with age, finding a way to solve this problem could help in the fight against aging, commented Susan Bailey of Colorado State University, author of the one of the studies.

Given the data collected so far, “there’s no reason why we can’t get to and from Mars safely,” Mason said.  

But “it is likely that we will not make several trips given the importance of the radiation,” he added.  

One study showed that mice exposed to radiation equivalent to 2.5 years in space suffered permanent kidney damage.

“Even if an astronaut can go to Mars, he or she may need dialysis upon return,” comments the lead author of one of the studies, Keith Siew, of the London Tubular Center, in a press release.

Another study suggests that female astronauts may better tolerate the stress of spaceflight. “This could be explained by the fact that women have to give birth to children, and therefore their bodies are more accustomed to major changes,” comments Christopher Mason.