When NASA astronauts Suni Williams and Butch Wilmore came back to Earth in March 2025 after being unexpectedly stranded on the International Space Station for nine months, it underscored the profound impact of space travel on the human body. Many noticed the evident changes in their appearance upon return, particularly Williams, who had grayer hair and a more pronounced chin. However, being away from Earth’s surface for extended periods can also lead to other effects such as bone and muscle loss, immune dysfunction, vision impairment, and even changes in brain structure. According to University of Florida physiologist Rachael Seidler, “The longer someone has been in space, the larger the magnitude of change” (via ScienceNews).
These effects have significant implications for visionaries like Elon Musk, who aim to send humans to Mars and beyond. Scientists point out that a major hurdle in these ambitions might be the risk of kidney damage during the two-year journey to Mars and back.
How space travel can cause kidney damage
A 2024 study published in Nature examined how space travel impacts kidney health, particularly during extended missions beyond Earth’s protective magnetic field. The researchers collected data from both real and simulated space environments, considering the effects of weightlessness and cosmic radiation.
The study explained that spaceflight affects kidney function, leading to increased calcium in urine, raising the risk of kidney stones for astronauts. Changes in kidney structure occur in response to space conditions. Additionally, cosmic radiation exposure akin to a Mars mission could cause kidney damage, including injury to blood vessels and impaired kidney function. More research is essential to develop treatments to protect astronauts’ kidney health for deep space missions.
Delving deeper into ‘cosmic kidney disease’
A 2024 literature review in Clinical Kidney Journal explored the condition known as “cosmic kidney disease.” Initially, it was believed astronauts developed kidney stones due to bone calcium loss in space, later excreted in urine.
However, recent findings show that space directly affects the kidneys and gut bacteria, which can also lead to kidney stones. Certain kidney proteins become less active, increasing calcium and oxalate excretion. Additionally, gut bacteria affecting oxalate levels proliferate. Spaceflight also causes the body to retain more water, concentrating urine, all contributing to kidney stones. A kidney stone attack in space could be dangerous and challenging to treat.
How cosmic radiation affects the kidneys
According to the Nature study, Galactic Cosmic Radiation (GCR) encountered during deep space missions can damage the kidneys in several ways. The kidneys, crucial for filtering waste and regulating blood pressure and electrolytes, are particularly sensitive to radiation, even at low doses similar to a Mars mission.
GCR consists of high-energy particles that can damage mitochondria, small structures in kidney cells essential for energy production. Since the kidney’s proximal tubules rely heavily on mitochondria, damage here can impair kidney function, leading to cell death and loss of function over time.
Moreover, radiation causes injury to the kidneys’ small blood vessels, leading to inflammation and vascular damage. This can result in conditions like thrombotic microangiopathy, where blood clots form in small vessels, further impairing kidney function.
The implications of chronic kidney injury
These radiation-induced injuries could lead to chronic kidney disease (CKD), fibrosis (scarring), and reduced blood filtering capacity over time. Although some damage may take months or years to develop, signs of kidney injury can appear soon after radiation exposure, according to the Nature study authors.
CKD, also known as kidney failure, occurs when kidneys can’t filter waste and excess fluid from the blood. When severe, the individual must undergo dialysis or receive a kidney transplant. (Read why dialysis might not be suitable for everyone with late-stage kidney disease.)
Kidney warning signs include nausea, vomiting, appetite loss, fatigue, sleep disturbances, urination changes, muscle cramps, difficulty concentrating, swelling in feet and ankles, dry skin, high blood pressure, shortness of breath, and chest pain.
How we might protect the kidneys during space travel
Despite the daunting prospect of radiation-induced kidney damage during space travel, NASA remains undeterred. “Some people think that radiation will keep NASA from sending people to Mars, but that’s not the current situation,” said Pat Troutman, NASA Human Exploration Strategic Analysis Lead. “We are optimistic that various mitigation techniques will lead to a successful Mars mission with a healthy crew that will live long and productive lives after returning to Earth.”
NASA is developing strategies to protect astronauts from GCR during deep space missions. Researchers are testing shielding materials for spacecraft, habitats, and spacesuits, while also exploring pharmaceutical countermeasures that might be more effective than shielding alone. Radiation-sensing instruments are being integrated into spacecraft, and astronauts use personal dosimeters aboard the space station. Engineers are advancing space weather forecasting tools and investigating faster rockets to limit time spent in space. NASA is also working on new radiation detection and mitigation technologies.
While challenges remain as we prepare to send humans to Mars, scientists see this as an opportunity to pioneer new medical advances that could protect astronauts in space and improve lives here on Earth.
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