Astronauts who make it to Mars and back may be given a unique badge of honor: “space kidney disease,” but it’s not as fun as it sounds: A new study suggests that the condition experienced by interplanetary travelers could fundamentally alter kidney structure and function, with prolonged exposure to microgravity and space radiation causing irreversible damage to these vital organs.
“A year on the space station would be equivalent to the amount of radiation a nuclear power plant worker could safely be exposed to over a five-year period,” the study authors say. Dr. Keith Shue But even on the ISS, astronauts will remain in low Earth orbit (LEO), and so will continue to be protected from galactic cosmic radiation (GCR) by the Earth’s magnetic field.
So far, the only humans who have been fully exposed to extraterrestrial radiation are the 24 people who traveled to the Moon as part of the Apollo program, but that return journey never lasted more than 12 days. In contrast, a visit to Mars could take years in deep space, where radiation levels would be much higher.
“In deep space missions, no one considers the possibility of radiation damaging the kidneys, even though they are one of the most radiation-sensitive organs,” Xu says.
For the study, the researchers analyzed kidney function and biomarkers in 66 astronauts, tested the kidneys of rodents that had traveled to the ISS, and performed a number of experiments to mimic the effects of long-distance space travel, including exposing mice and rats to radiation levels equivalent to what astronauts would receive on a multi-year trip to Mars.
The results revealed that within less than a month in space, significant “remodeling” of the kidneys occurs, with key sections called the distal tubules shortening due to the effects of microgravity and radiation. This in turn leads to a “progressive and irreversible” loss of kidney function, although it is unclear how this impacts a Mars mission.
“The kidneys are slow-responding organs, so you don’t notice anything wrong until much later. You can lose 75 percent of your kidney function before you experience symptoms and your function starts to decline,” Siu says. As a result, astronauts can “feel totally normal” during their mission, but then experience catastrophic kidney failure after returning to Earth.
“It’s like high blood pressure damages your heart, and one day you have a heart attack,” Siu explains.
While that’s a scary prospect for a spacesuited human, if the effects are delayed long enough it may not harm the mission itself, but a more immediate concern is kidney stones, which are up to 14 times more common during spaceflight than on Earth and can incapacitate astronauts at critical moments.
Until now, the increased risk of kidney stones in space has been mainly attributed to bone demineralization caused by microgravity, but the researchers’ metabolic analysis suggests that reduced kidney function may also play a role. “Just repairing bones won’t solve this problem,” Siu says. “We also need to look at repairing the kidneys.”
Despite the significance of these findings, the researchers stress that their model may not accurately represent the effects of spaceflight, as the rodents were exposed to up to two and a half years of GCR in just 45 minutes. It is unclear whether the effects of this acute exposure are comparable to the chronic exposure faced by interplanetary travelers.
“It’s entirely possible that what we’re seeing are the effects of acute radiation that you never actually get,” Siu explains. “So what we’re seeing may be less harmful than what actually happens, or we may be overestimating the damage,” he says, adding that long-term exposure to low doses could be like “dying from a thousand paper cuts.”
Commenting on these findings, statement“Kidneys are really important if you’re planning a space mission,” said lead study author Professor Stephen B. Walsh. “Although we can’t use shielding to protect the kidneys from galactic radiation, learning more about kidney biology may allow us to develop technological or pharmaceutical measures to facilitate long-term space travel.”
“Drugs developed for astronauts may also be beneficial on Earth, for example by enabling the kidneys of cancer patients to tolerate higher radiation therapy doses. The kidneys are one of the limiting factors in this regard.”
The study was published in the journal Nature Communications.