Astronauts who make a round trip to Mars may be awarded a unique badge of honor in the form of “space kidney disease,” which is a lot less fun than it sounds. According to a new study, the conditions experienced by interplanetary travelers can radically change the structure and function of the kidney, with prolonged exposure to microgravity and cosmic radiation causing irreversible damage to this vital organ.
“To put it in perspective, one year on the space station is equivalent to the same dose of radiation that a nuclear power plant worker would safely receive in five years,” study author Dr. Keith Xu told IFLScience. Even on the ISS, however, astronauts remain in low Earth orbit (LEO) and therefore continue to receive protection from the Earth’s magnetic field against galactic cosmic radiation (GCR).
Until now, the only people ever fully exposed to GCR were the 24 individuals who traveled to the Moon as part of the Apollo missions, but those return trips never lasted more than 12 days. By contrast, a visit to Mars would likely require several years in deep space, which adds an awful lot more radiation.
“On deep space missions, no one even thought that the kidney could be damaged by radiation, even though it is among the most radiosensitive organs,” says Xu.
In their study, the researchers analyzed kidney function and biomarkers from 66 astronauts and examined the kidneys of rodents that traveled to the ISS. They also conducted a series of experiments designed to mimic the effects of long-distance space travel, bombarding mice and rats with the equivalent dose of radiation an astronaut would receive on a multi-year trip to Mars.
The results revealed significant “remodeling” of the kidney after less than a month in space, with a key component known as the distal convoluted tubule becoming shorter as a result of microgravity and radiation. This in turn leads to a “progressive and irreversible” loss of kidney function, although exactly what impact this will have on a mission to Mars remains unclear.
“The kidney is a late-reacting organ, so you don’t see anything wrong until much later. You can lose 75 percent of function before you really start to see the right symptoms and lose weight,” says Siew. As a result, astronauts can “feel perfectly normal” during a mission, only to experience catastrophic kidney failure after returning to Earth.
“It’s like you have high blood pressure and your heart gets damaged, and then one day you have a heart attack,” Sue explains.
As horrible as this sounds to the man in the space suit, if the effects are delayed long enough, it may not harm the mission itself. A more serious concern, however, 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 largely been attributed to bone demineralization as a result of microgravity, but the researchers’ metabolic analyzes suggest that loss of kidney function may also be partly to blame. “You can’t solve this problem by just trying to fix the bones. You have to take care of the kidney as well,” says Siew.
Despite the seriousness of these findings, the researchers stress that their models may not accurately represent the effects of spaceflight, as they blasted their rodents with up to two and a half years of GCR in short bursts of just 45 minutes. Whether the impact of this acute exposure matches the chronic exposure faced by interplanetary travelers remains unclear.
“There’s a real possibility that what we’re seeing is an effect of acute radiation that you wouldn’t really be exposed to,” Siew explains. “So what we’re looking at may actually be less harmful than what’s really going to happen.” Or it could be that we’re overestimating the damage,” he says, adding that prolonged exposure to lower doses can be like “death by a thousand paper cuts.”
Commenting on these findings in a statement, senior study author Professor Stephen B. Walsh said that “if you’re planning a space mission, kidneys really do matter. You can’t protect them from galactic radiation using shielding, but as we learn more about kidney biology, it may be possible to develop technological or pharmaceutical measures to facilitate extended space travel.
“Any drugs developed for astronauts could also be useful here on Earth, for example by allowing the kidneys of cancer patients to tolerate higher doses of radiotherapy, the kidneys being one of the limiting factors in this respect.”
The research was published in the journal Nature Communications.
