Astronauts who make the round-trip flight to Mars may be rewarded with a unique accolade in the form of “cosmic kidney disease,” but it’s 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 causing irreversible damage to this vital organ.
“To put it in perspective: one year in the space station corresponds to the same radiation dose that a worker in a nuclear power plant is guaranteed to receive in five years,” study author Dr. Keith Siew told IFLScience. But even on the ISS, astronauts remain in low Earth orbit (LEO) and are therefore still protected from galactic cosmic radiation (GCR) by the Earth’s magnetic field.
To date, the only people ever fully exposed to GCR were the 24 people who flew to the Moon on the Apollo missions, but those round-trip flights never lasted more than 12 days. In contrast, a visit to Mars will likely require several years in space, resulting in significantly higher levels of radiation.
“During space missions, no one even thought that the kidney could be damaged by radiation, even though it is 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 series of experiments to mimic the effects of long-distance space travel by bombarding mice and rats with the same dose of radiation that an astronaut would receive on a multi-year trip to Mars.
The results showed that the kidney had undergone significant “remodeling” after less than a month in space. A key component, called the distal tubule, shortened as a result of microgravity and radiation. This in turn led to a “progressive and irreversible” loss of kidney function. However, the exact impact this would have on a mission to Mars is still unclear.
“The kidney is a late-reacting organ, so you don’t notice until much later when something is wrong. It can lose 75 percent of its function before you really notice symptoms and a decline in performance,” says Siew. As a result, astronauts can “feel perfectly normal” during a mission, only to suffer catastrophic kidney failure upon returning 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 that sounds for the person in the spacesuit, if the effects are delayed long enough, it might not harm the mission itself. More pressing, however, are kidney stones, which are up to 14 times more common during space flights than on Earth and can incapacitate astronauts at critical moments.
Until now, the increased risk of kidney stones in space has been largely attributed to bone demineralization caused by microgravity, but the researchers’ metabolic analyses suggest that loss of kidney function may also be partly to blame. “You can’t solve this problem by just trying to repair the bones. You have to try to repair the kidneys as well,” Siew says.
Despite the seriousness of these findings, the researchers stress that their models may not accurately reflect the effects of spaceflight, as they exposed their rodents to up to two and a half years’ worth of GCR radiation in short bursts of just 45 minutes. Whether the effects of this acute exposure are comparable to the chronic exposure experienced by interplanetary travelers remains unclear.
“There is a real possibility that we are observing the effects of acute radiation that one would not actually be exposed to,” Siew explains. “So what we are observing could be less harmful than what will actually happen. Or we are overestimating the harm,” he says, adding that prolonged exposure to lower doses could be like “death by a thousand paper cuts.”
Commenting on these results in a statement, lead study author Professor Stephen B. Walsh said: “When planning a space mission, the kidneys are really important. 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 interventions that enable longer space travel.”
“All drugs developed for astronauts could also be useful here on Earth, for example by making the kidneys of cancer patients more tolerant to higher doses of radiation, because the kidneys are one of the limiting factors in this respect.”
The study was published in the journal Nature Communications.