According to Gram Research analysis of 12 astronauts, urinary oxalate increases by approximately 12% during long-duration spaceflight, rising from 37.9 mg per day before launch to 42.3 mg per day in space, even when astronauts eat the same controlled diet. This elevation persists throughout the entire mission and normalizes after returning to Earth, suggesting that microgravity itself alters how the body processes oxalate independent of dietary intake.
Gram Research analysis of 12 astronauts during long space missions found that their bodies release more oxalate (a substance linked to kidney stones) into their urine while in space, even when eating the same diet as on Earth. Researchers discovered that urinary oxalate jumped from 37.9 mg per day before flight to 42.3 mg per day in space, and this increase persisted throughout their missions. The study suggests that microgravity itself may change how the body processes oxalate, independent of what astronauts eat. Understanding this effect could help protect astronauts’ kidney health during future long-duration missions to the Moon and Mars.
Key Statistics
A 2026 exploratory analysis of 12 astronauts found that urinary oxalate increased from 37.9 mg per day before spaceflight to 42.3 mg per day during long-duration missions, a statistically significant 12% increase that persisted throughout the in-flight phase.
According to research reviewed by Gram, urinary calcium more than doubled during spaceflight, increasing from 178.9 mg per day pre-flight to 270.3 mg per day in space, suggesting that microgravity triggers substantial changes in mineral metabolism.
A 2026 study of 12 astronauts found that for every 1 mg increase in dietary oxalate, urinary oxalate increased by 0.050 mg during spaceflight, demonstrating that diet influences oxalate excretion but does not fully explain the spaceflight effect.
Post-flight urinary oxalate dropped to 31.5 mg per day in the 2026 astronaut study, falling below pre-flight levels of 37.9 mg per day and indicating that the spaceflight-induced increase in oxalate excretion is reversible upon return to Earth.
The Quick Take
- What they studied: How the weightless environment of space affects the amount of oxalate (a chemical compound) that astronauts’ bodies release into their urine, and whether diet plays a role in this change.
- Who participated: 12 astronauts on long-duration space missions who ate controlled diets provided by their space agencies. Researchers measured their urine before launch, during their time in space, and after returning to Earth.
- Key finding: Astronauts’ urinary oxalate increased by about 12% during spaceflight (from 37.9 to 42.3 mg per day), and this elevation continued throughout their entire mission even though their diet stayed the same. After returning to Earth, oxalate levels dropped back down to below pre-flight levels.
- What it means for you: If you’re not an astronaut, this research is primarily important for space agencies planning long missions. However, it reveals how microgravity affects human metabolism in ways we don’t fully understand yet. For the general public, this highlights why astronaut health research matters for advancing space exploration.
The Research Details
Researchers collected detailed information from 12 astronauts on three separate occasions: before they launched into space, while they were living aboard the International Space Station or other spacecraft, and after they returned to Earth. During each period, the astronauts provided 24-hour urine samples (all urine collected in one day), which were tested to measure calcium and oxalate levels. The astronauts also kept detailed food records so researchers could track exactly how much calcium and oxalate they consumed each day.
The researchers used a statistical method called mixed-effects modeling to analyze the data. This approach allowed them to account for differences between individual astronauts while looking at overall patterns. They adjusted their analysis to account for how much calcium and oxalate each person ate, so they could separate the effects of diet from the effects of being in space.
This study design is particularly valuable because the astronauts ate controlled diets provided by space agencies, meaning researchers knew exactly what they consumed. This eliminates the confusion that would come from people eating different foods, making it easier to spot the true effects of spaceflight itself.
Most studies about kidney stone risk focus on diet and genetics here on Earth. This research is important because it shows that the space environment itself, independent of what people eat, can change how the body processes oxalate. Understanding these microgravity-related changes is crucial for protecting astronauts’ health during long missions to the Moon and Mars, which could last many months or years.
This study has several strengths: it used controlled diets so researchers knew exactly what participants consumed, it measured actual urine output rather than relying on estimates, and it followed the same people across three time periods (before, during, and after spaceflight). However, the sample size of 12 astronauts is relatively small, which means results may not apply equally to all people. The study is exploratory, meaning it identifies patterns that need further investigation rather than providing definitive answers. Additionally, astronauts represent a highly selected, healthy population, so findings may not apply to the general public.
What the Results Show
The most striking finding was that urinary oxalate increased significantly during spaceflight. Before launch, astronauts excreted an average of 37.9 mg of oxalate per day in their urine. During their time in space, this jumped to 42.3 mg per day, an increase of about 12%. This increase was statistically significant, meaning it was unlikely to occur by chance alone.
Urinary calcium also increased during spaceflight, rising from 178.9 mg per day before launch to 270.3 mg per day in space, an increase of about 51%. However, the relationship between calcium and oxalate was interesting: dietary calcium intake did not predict how much oxalate appeared in the urine. This suggests that calcium intake alone doesn’t explain the oxalate changes.
After astronauts returned to Earth, both measurements normalized. Urinary calcium dropped to 185.8 mg per day, and urinary oxalate fell to 31.5 mg per day, which was actually lower than pre-flight levels. This pattern suggests that the spaceflight environment directly caused the increase, rather than any permanent change to the body.
Dietary oxalate intake remained relatively stable before and during spaceflight (382.0 mg per day pre-flight versus 339.4 mg per day in-flight), but decreased after return to Earth (241.6 mg per day). The key finding was that for every 1 mg increase in dietary oxalate, urinary oxalate increased by 0.050 mg, showing that diet does influence oxalate excretion, but doesn’t fully explain the spaceflight effect.
The research revealed important individual differences among astronauts. Some astronauts showed elevated oxalate levels even before spaceflight, and these individuals experienced even greater increases once in space. This suggests that certain people may be more susceptible to developing high urinary oxalate in microgravity, possibly due to genetic factors or individual differences in how their bodies absorb and process oxalate. This inter-individual variation is important because it means mitigation strategies may need to be personalized rather than one-size-fits-all.
Previous research has documented that astronauts experience bone loss and changes in calcium metabolism during spaceflight, a well-known effect of microgravity. This new study extends that knowledge by showing that oxalate metabolism is also affected. The findings align with earlier observations that kidney stone risk may be elevated in astronauts, though direct kidney stone formation was not measured in this study. The research suggests that the mechanism involves changes in how the body processes oxalate in microgravity, not just dietary factors.
The study included only 12 astronauts, which is a small sample size that limits how broadly the findings apply. All participants were highly trained, healthy individuals selected for spaceflight, so results may not reflect how microgravity affects the general population. The study measured urinary oxalate but did not directly assess kidney stone formation, so we cannot definitively say that increased urinary oxalate translates to more kidney stones in space. The research is exploratory, meaning it identifies patterns that need confirmation through larger studies. Additionally, the mechanisms behind why microgravity increases oxalate excretion remain unclear and require further investigation.
The Bottom Line
For astronauts: Space agencies should consider monitoring urinary oxalate levels during long missions and may want to adjust dietary oxalate intake or timing of calcium supplementation to reduce kidney stone risk. The evidence suggests that reducing dietary oxalate intake during spaceflight could help, though individual responses vary. For the general public: This research doesn’t directly apply to everyday life on Earth, but it demonstrates the importance of understanding how extreme environments affect human health.
Space agencies planning long-duration missions should prioritize this research, as protecting astronaut health is essential for successful exploration. Astronauts themselves should be aware of potential kidney stone risk during spaceflight. Researchers studying bone health, calcium metabolism, and kidney stone prevention may find these findings relevant. The general public should understand that this research helps advance space exploration safety, though it doesn’t change current recommendations for kidney stone prevention on Earth.
The changes in urinary oxalate occurred within days to weeks of entering space, based on the timing of urine collections. The elevation persisted throughout the entire spaceflight duration, which ranged from several weeks to several months depending on the mission. Recovery to near pre-flight levels occurred within days to weeks after returning to Earth, suggesting the effect is reversible.
Frequently Asked Questions
Do astronauts get kidney stones more often in space?
This study didn’t measure actual kidney stone formation, but it found that astronauts’ bodies release more oxalate into urine during spaceflight, which is a risk factor for kidney stones. Urinary oxalate increased 12% in space, suggesting elevated kidney stone risk that space agencies should monitor.
Can astronauts prevent high oxalate levels by changing their diet in space?
Partially. The study found that reducing dietary oxalate helps lower urinary oxalate, but spaceflight itself causes additional oxalate elevation beyond diet alone. Researchers suggest timed calcium intake with meals may help, but individual responses vary significantly among astronauts.
Does this research apply to people on Earth?
Not directly. This study examined how microgravity specifically affects oxalate metabolism in highly trained astronauts. The findings don’t change kidney stone prevention recommendations for people living on Earth, though they advance our understanding of how extreme environments affect human health.
Why does spaceflight increase urinary oxalate if diet stays the same?
The exact mechanism remains unclear, but researchers believe microgravity alters how the body absorbs and processes oxalate. The study shows the effect is real and reversible, but further investigation is needed to understand the underlying biological changes.
How long does it take for oxalate levels to return to normal after spaceflight?
Based on this study, urinary oxalate normalized within days to weeks after astronauts returned to Earth. Post-flight measurements showed oxalate levels dropped to 31.5 mg per day, actually lower than pre-flight levels of 37.9 mg per day, indicating rapid recovery.
Want to Apply This Research?
- For astronauts or space mission planners: Track daily dietary oxalate intake (in mg) and correlate with weekly urinary oxalate measurements. Set a target to maintain dietary oxalate below 300 mg per day during spaceflight based on this study’s findings.
- Implement timed calcium supplementation during meals high in oxalate-containing foods to reduce oxalate absorption. Log which foods are consumed and when calcium supplements are taken to identify patterns that minimize urinary oxalate elevation.
- Establish a baseline urinary oxalate measurement before spaceflight begins. Collect 24-hour urine samples weekly during the mission and compare to baseline. Track dietary oxalate intake daily using a food logging system. After return to Earth, continue monitoring for 2 to 4 weeks to confirm normalization of oxalate levels.
This research describes findings from a small exploratory study of 12 astronauts and should not be interpreted as medical advice for the general population. The study does not measure actual kidney stone formation and does not establish definitive cause-and-effect relationships. Individuals concerned about kidney stone risk should consult with a healthcare provider. Space agencies and mission planners should use these findings as part of comprehensive health monitoring protocols for astronauts on long-duration missions. This research is preliminary and requires confirmation through larger studies before implementing widespread mitigation strategies.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.