Astronauts’ kidneys may not survive a roundtrip to Mars

Space flight significantly alters kidney structure and function, with galactic radiation causing permanent damage, which could jeopardize any mission to Mars, according to new research led by University College London (UCL). 

This study is the most extensive analysis of kidney health in space to date and includes the first health dataset for commercial astronauts.

Space flight and health issues

Researchers have known since the 1970s that space flight causes various health issues, such as bone mass loss, heart and eyesight weakening, and kidney stone development. 

These problems are believed to stem from exposure to space radiation, including solar winds from the Sun and Galactic Cosmic Radiation (GCR) from deep space, from which Earth’s magnetic field partially shields astronauts in Low Earth orbit (LEO). 

However, the 24 individuals who traveled to the moon experienced unmitigated GCR exposure for only short durations.

Kidney response to space flight 

The current study aimed to explore how the kidneys respond to space flight conditions. A UCL-led team from over 40 institutions across five continents conducted various experiments and analyses, using data and samples from 20 study cohorts. 

This included samples from over 40 LEO space missions involving humans and mice, mostly from the International Space Station, and 11 space simulations involving mice and rats. 

Seven of these simulations exposed mice to simulated GCR doses equivalent to 1.5-year and 2.5-year Mars missions, replicating space flight beyond Earth’s magnetic field.

Kidneys are remodeled in space 

The results indicated that both human and animal kidneys are ‘remodeled’ in space, with kidney tubules responsible for calcium and salt balance showing signs of shrinkage after less than a month. 

This change is likely due to microgravity rather than GCR, although further research is needed to determine if the interaction between microgravity and GCR can worsen these structural changes.

Kidney stone formation 

Previously, the primary reason for kidney stone formation in space was assumed to be microgravity-induced bone loss leading to a calcium build-up in the urine. 

However, the recent findings suggest that space flight fundamentally alters how kidneys process salts, likely contributing to kidney stone formation.

A particularly concerning finding for potential Mars missions is that mice exposed to simulated GCR for 2.5 years experienced permanent kidney damage and loss of function.

Astronauts on long space missions

“We know what has happened to astronauts on the relatively short space missions conducted so far, in terms of an increase in health issues such as kidney stones. What we don’t know is why these issues occur, nor what is going to happen to astronauts on longer flights such as the proposed mission to Mars,” said lead author Keith Siew, an expert in renal medicine at UCL.

“If we don’t develop new ways to protect the kidneys, I’d say that while an astronaut could make it to Mars they might need dialysis on the way back. We know that the kidneys are late to show signs of radiation damage; by the time this becomes apparent it’s probably too late to prevent failure, which would be catastrophic for the mission’s chances of success.”

Facilitating extended space travel 

“Our study highlights the fact that if you’re planning a space mission, kidneys really matter,” added senior author Stephen B. Walsh, a professor at the same university. 

“You can’t protect them from galactic radiation using shielding, but as we learn more about renal biology it may be possible to develop technological or pharmaceutical measures to facilitate extended space travel.” 

“Any drugs developed for astronauts may also be beneficial here on Earth, for example by enabling cancer patients’ kidneys to tolerate higher doses of radiotherapy, the kidneys being one of the limiting factors in this regard.”

Though the study, published in the journal Nature Communications, only describes kidney health up to two and a half years, it provides the most comprehensive data available for this timeframe. 

The findings underscore the necessity of addressing these health challenges to ensure the success of long-duration space missions, such as those to Mars.

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