As humanity prepares for manned missions to Mars, a new study led by University College London (UCL) reveals a new potential health risk for astronauts. Published in Nature Communications, the study highlights the damaging effects of space travel on kidney health, with implications that could jeopardize the success of long-duration space missions.

Scientists from over 40 institutions across five continents conducted the most extensive analysis of kidney health during space flight to date. The study included data and samples from over 40 Low Earth Orbit (LEO) space missions with humans and mice and 11 space simulations using rodents. The simulations exposed subjects to Galactic Cosmic Radiation (GCR) doses equivalent to 1.5-year and 2.5-year Mars missions, replicating conditions outside Earth’s magnetic field.

Since the 1970s, it has been understood that space flight leads to various health problems such as bone mass loss, heart weakening, vision issues, and kidney stones. These problems are often attributed to exposure to microgravity and space radiation, such as solar winds and GCR. While most manned space flights occur in LEO, where astronauts are provided partial protection from Earth’s magnetic field, only the 24 astronauts who traveled to the moon experienced unmitigated GCR. And even those were only for short durations (6-12 days).

“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,” said Keith Siew, first author of the study from the London Tubular Centre, based at the UCL Department of Renal Medicine. “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.

Before this study, there had been no comprehensive investigation into how kidneys are affected during prolonged space travel outside Earth’s protective magnetic field. It turns out that there could be more damage potential than originally believed.

The study found that both human and animal kidneys undergo significant remodeling in space. Specific kidney tubules, responsible for fine-tuning calcium and salt balance, showed signs of shrinkage after less than a month in space. The likely cause of this shrinkage is microgravity, though further research is required to determine if the interaction of microgravity and GCR could accelerate or worsen these structural changes.

“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,” Siew said. “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.”

The primary cause of kidney stone formation during space missions was previously assumed to be microgravity-induced bone loss leading to calcium buildup in the urine. However, the study suggests that space flight fundamentally alters how kidneys process salts, likely contributing to kidney stone formation.

The most alarming finding for prospective Mars astronauts is that mice exposed to radiation-simulating GCR for 2.5 years experienced permanent kidney damage and loss of function.

“Our study highlights the fact that if you’re planning a space mission, kidneys really matter,” said Stephen B. Walsh, senior author of the study from the London Tubular Centre, UCL. “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.”