Space Flight Destroys Your Red Blood Cells

It’s really true: space wants to kill us. And this time, space is trying to kill us from the inside out.

A new study on astronauts living on board the International Space Station shows that while in space, the astronauts’ bodies destroyed 54 percent more red blood cells than they normally would on Earth. Even one year after their flight and back on Earth, the symptoms of “space anemia” persisted in the 14 astronauts tested.

Anemia in astronauts has been known as an issue, even since some of the first human missions to space. Medical experts haven’t been sure, however, about the mechanisms contributing to anemia in space. For quite some time, it was thought that space anemia was part of the fluid shift in astronauts when they arrive in space due to the zero-gravity conditions.

Upon entry into microgravity, body fluids tend to migrate away from the legs toward the upper body and head, with the usual result of nasal congestion, a feeling of fullness in the head and faces that look puffy. This fluid shift has also been part of the studies of why astronauts’ vision degrades while in space.

Previous studies showed that astronauts lose 10 percent of the liquid in their blood vessels while their bodies adapt to being in space. From those studies, it was thought vascular systems in the space environment rapidly destroyed 10 percent of the red blood cells to restore the balance, and that red blood cell control was back to normal after 10 days in space.

Astronaut Tim Peake’s first blood draw completed in space. The sample was taken as part of the anemia study. Credit: NASA.

Instead, a team led by Dr. Guy Trudel from the Ottawa Hospital and University of Ottawa, found that the red blood cell destruction was a primary effect of being in space, not just caused by fluid shifts. Plus, the rate of red blood cell destruction persisted, albeit at a lower rate, for at least a year following the astronauts’ six-month expeditions in space.

“Here, we show that space flight is associated with persistently increased levels of products of hemoglobin degradation, carbon monoxide in alveolar air and iron in serum, in 14 astronauts throughout their 6-month missions onboard the International Space Station,” Trudel and his team wrote in their paper, published in Nature Medicine. “One year after landing, erythrocytic effects persisted, including increased levels of hemolysis, reticulocytosis and hemoglobin.”

These findings, the team said, suggest that the destruction of red blood cells, called hemolysis, is a primary effect of microgravity in space flight and support the hypothesis that the anemia associated with space flight is a hemolytic condition that should be considered in the screening and monitoring of both astronauts and space tourists.

Red blood cell destruction happens all the time in our bodies. On Earth, our bodies create and destroy 2 million red blood cells every second. The researchers found that astronauts’ bodies were destroying 54 percent more red blood cells during the six months they were in space, or 3 million every second. These results were the same for both female and male astronauts.

But the effects of this type of anemia aren’t evident until the astronauts return to Earth.

“Thankfully, having fewer red blood cells in space isn’t a problem when your body is weightless,” said Trudel, in a press release. “But when landing on Earth and potentially on other planets or moons, anemia affecting your energy, endurance, and strength can threaten mission objectives. The effects of anemia are only felt once you land, and must deal with gravity again.”

Astronaut David Saint-Jacques collecting breath, ambient air, and blood samples for the MARROW experiment. Credit: NASA

In this study, five out of 13 astronauts were clinically anemic when they landed—one of the 14 astronauts did not have blood drawn on landing. While the researchers found that the anemia slowly improved after a few months, even one year after astronauts returned to Earth, red blood cell destruction was still 30 percent above preflight levels. The team said these results suggest that structural changes may have happened to the astronaut while they were in space that changed red blood cell control for up to a year after long-duration space missions.

What does this mean for future space travelers? Trudel’s team said that everyone going to space should be screened for existing blood or health conditions that are affected by anemia. But also, since the study showed that the longer the space mission, the worse the anemia, this could impact long-duration missions to the Moon and Mars, since it is unclear at this point how long the body can withstand the higher rate of destruction and production of red blood cells. The researchers suggest an adapted diet for astronauts to try to counteract the anemia.

As with most physiological studies in space, these findings are applicable to people on Earth. Trudel wants to study this correlation in future studies.

“If we can find out exactly what’s causing this anemia, then there is a potential to treat it or prevent it, both for astronauts and for patients here on Earth,” said Trudel.

Lead image caption: Flight Engineer Anne McClain in the cupola holding biomedical gear for MARROW. Credit: NASA
Sources: Nature Medicine
Ottawa Hospital Press Release

Nancy Atkinson

Nancy has been with Universe Today since 2004, and has published over 6,000 articles on space exploration, astronomy, science and technology. She is the author of two books: "Eight Years to the Moon: the History of the Apollo Missions," (2019) which shares the stories of 60 engineers and scientists who worked behind the scenes to make landing on the Moon possible; and "Incredible Stories from Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos" (2016) tells the stories of those who work on NASA's robotic missions to explore the Solar System and beyond. Follow Nancy on Twitter at and and Instagram at and

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