Astronauts who make the return trip to Mars may be rewarded with 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 kidney, with long-term 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 is safely allowed in five years,” study author Dr Keith Siew told IFLScience. However, even on the ISS, astronauts remain in Low Earth Orbit (LEO) and therefore continue to receive protection from the Earth’s magnetic field against Galactic Cosmic Rays (GCR).
To date, the only people who have ever been fully exposed to GCR are the 24 individuals who traveled to the moon on the Apollo missions, but those return trips never lasted more than 12 days. In contrast, a visit to Mars will likely require several years in deep space, resulting in much more radiation.
“On deep space missions, no one even thinks that the kidney could be damaged by radiation, even though it is one of the most sensitive organs to radiation,” says Siew.
In their study, the researchers analyzed renal function and biomarkers from 66 astronauts and examined the kidneys of rodents who 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 shortened due to microgravity and radiation. This in turn leads to a “progressive and irreversible” loss of kidney function, although it’s not clear exactly what impact this would have on a Mars mission.
“The kidney is a late-responder organ, so you don’t see anything wrong until much later. You can lose 75 percent of function before you actually start seeing the right symptoms and regressing,” says Siew. As a result, astronauts may “feel perfectly normal” during a mission, but experience catastrophic kidney failure upon return to Earth.
“It’s like you have high blood pressure and your heart is damaged, and then one day you have a heart attack,” explains Siew.
As terrifying as this sounds to a human in a spacesuit, if the effects are delayed long enough, it may not harm the mission itself. But of more pressing concern are kidney stones, which occur up to 14 times more frequently 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 due to microgravity, but the researchers’ metabolic analyzes suggest that the loss of kidney function may also be partly to blame. “You’re not going to solve this problem by trying to fix the bones.” You also need to look at kidney repair,” says Siew.
Despite the seriousness of these findings, the researchers stress that their models may not accurately represent the effects of spaceflight, as they exposed their rodents to up to two and a half years of GCR in short doses of just 45 minutes. It is not clear whether the impact of this acute exposure matches the chronic exposure faced by interplanetary travelers or not.
“There’s a real possibility that what we’re seeing is the effects of acute radiation that you wouldn’t actually be exposed to,” Siew explains. “So what we’re looking at may actually be less harmful than what actually happens.” Or it could be that we’re overestimating the damage,” he says, adding that long-term exposure to lower doses can be like “death by a thousand paper cuts.”
Commenting on the findings in a statement, lead study author Professor Stephen B. Walsh said that “kidneys really matter if you’re planning a space mission. You can’t shield them from galactic radiation, but as we learn more about kidney biology, it may be possible to develop technological or pharmaceutical measures to facilitate longer space travel.”
“Any drugs developed for astronauts may also be beneficial here on Earth, for example by enabling the kidneys of cancer patients to tolerate higher doses of radiotherapy, where the kidneys are one of the limiting factors.”
The study was published in the journal Nature Communications.