Astronauts who make the round trip to Mars can be awarded a unique badge of honor in the form of “space kidney disease,” which is a hell of a lot less fun than it sounds. According to new research, the conditions experienced by interplanetary travelers can radically alter the structure and function of the kidneys, with prolonged exposure to microgravity and space radiation producing irreversible damage to this vital organ.
“To put it in perspective, one year on the space station is equivalent to the same radiation dose that a nuclear power plant worker is safely allowed in five years,” study author Dr Keith Siew 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).
So far, the only people who have been fully exposed to GCR are the 24 individuals who traveled to the Moon as part of the Apollo missions, however these 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 enormous amount of radiation.
“On deep space missions, no one thinks that the kidney can be damaged by radiation, despite it being among the most radio-sensitive organs,” says Siew.
In their study, the researchers analyzed kidney function and biomarkers from 66 astronauts and examined the kidneys of rodents that had traveled to the ISS. They also conducted a number 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, results in “progressive and irreversible” loss of kidney function, although exactly what impact this would have on a Mars mission remains unclear.
“The kidney is a late-responding organ, so you don’t see anything wrong until much later. You can lose 75 percent of function before you start seeing the right symptoms and crash,” says Siew. As a result, astronauts can “feel completely normal” during a mission, only to experience catastrophic kidney failure after return to Earth.
“It’s like having high blood pressure and heart damage, and then one day you have a heart attack,” Siew explains.
As terrifying as this sounds to the man in the spacesuit, if the effects are delayed long enough, then it may not harm the mission itself. However, the most pressing concern is kidney stones, which are up to 14 times more common during spaceflight than on Earth and can put astronauts out of action at critical moments.
Until now, the increased risk of kidney stones in space was largely attributed to bone demineralization as a result of microgravity, but the researchers’ metabolic analyzes suggest that the loss of kidney function may also be partly to blame. “You can’t solve this problem just by trying to fix the bones. You also have to look at the arrangement of the kidney,” says Siew.
Despite the seriousness of these findings, the researchers note that their models may not accurately represent the effects of spaceflight, as they blasted their rodents with up to two and a half years’ worth of GCR in short bursts of just 45 minutes. Whether or not 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 are effects of acute radiation that you wouldn’t actually be exposed to,” Siew explains. “So what we’re seeing may actually be less harmful than what will actually happen. Or it could be that we’re overestimating the harm,” 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 matter. 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 drug developed for astronauts could also be useful here on Earth, for example by enabling the kidneys of cancer patients to tolerate higher doses of radiotherapy, the kidneys being one of the limiting factors in this regard.”
The study is published in the journal Nature Communications.