Astronauts who make the round trip to Mars may be rewarded with a unique badge of honor in the form of “cosmic kidney disease,” which is 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 long-term exposure to microgravity and space 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 could safely receive in five years,” study author Dr. Keith Siew told IFLScience. However, even on the ISS, astronauts remain in low Earth orbit (LEO) and therefore remain protected from Earth’s magnetic field against galactic cosmic rays (GCR).
To date, the only people ever fully exposed to GCR are the 24 individuals who traveled to the moon as part of the Apollo missions, but these return trips never lasted longer than twelve days. In contrast, a visit to Mars will likely require several years in deep space, which means a lot more radiation.
“During space missions, no one even thought that the kidney could be damaged by radiation, despite it being one of the most radiation-sensitive organs,” says Siew.
In their study, the researchers analyzed the kidney function and biomarkers of 66 astronauts and examined the kidneys of rodents that had traveled to the ISS. They also conducted a number of experiments to simulate the effects of long-distance space travel, bombarding mice and rats with the equivalent dose of radiation that an astronaut would receive during 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 shortening due to microgravity and radiation. This in turn results in a “progressive and irreversible” loss of kidney function, although exactly what impact this would have on a mission to Mars remains unclear.
“The kidney is an organ that reacts late, so you only see that something is wrong much later. You can lose 75 percent of your functioning before you really start to see the right symptoms and decline,” says Siew. As a result, astronauts can “feel completely normal” during a mission, only to experience catastrophic kidney failure upon return to Earth.
“It’s like if you have high blood pressure and your heart gets damaged, and then one day you have a heart attack,” Siew explains.
As terrible as this sounds to the human in the space suit, if the effects are delayed long enough it won’t harm the mission itself. Of more pressing concern, however, are 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 has been largely attributed to bone demineralization due to microgravity, but the researchers’ metabolic analyzes suggest that 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 repairing the kidney,” says Siew.
Despite the severity of these findings, the researchers emphasize that their models may not accurately capture the effects of spaceflight, as they bombarded their rodents with as much as 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 looking at may be less damaging than what will actually happen. Or it could be that we are overestimating the damage,” he says, adding that long-term exposure to lower doses could be akin to “death by a thousand paper cuts.”
Commenting on these findings, senior study author Professor Stephen B. Walsh said: “If you’re planning a space mission, the kidneys really matter. You can’t protect them from galactic radiation with shielding, 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 could also be useful here on Earth, for example by enabling the kidneys of cancer patients to tolerate higher doses of radiotherapy, with the kidneys being one of the limiting factors in this regard.”
The study has been published in the journal Nature Communications.