Space Is Destroying Astronauts’ Red Blood Cells

The discovery could complicate long-term space travel, including future Mars missions

A male NASA astronaut Tim Kopra performs blood draw on European Space Agency astronaut Tim Peake on the international space station
NASA astronaut Tim Kopra (left) performs blood draw on European Space Agency (ESA) astronaut Tim Peake for the recent study. NASA

Space travel takes many tolls on the human body, and new research suggests long-duration flights are changing astronauts' blood. According to the study published in the journal Nature Medicine, astronauts’ bodies are destroying their own blood cells while in space at higher rates than on Earth. 

"Space anemia has consistently been reported when astronauts returned to Earth since the first space missions, but we didn't know why," says study author Guy Trudel, a rehabilitation physician and researcher at The Ottawa Hospital and professor at the University of Ottawa in Canada, in a statement. “Our study shows that upon arriving in space, more red blood cells are destroyed, and this continues for the entire duration of the astronaut’s mission.”

Before this study, space anemia was thought to be a short-term adaptation of the human body, but the work reveals the impacts last at least a year after returning to terra firma. A drop in red blood cell counts is concerning because these special cells contain a protein called hemoglobin, which carries oxygen from the lungs to the rest of the body. A lack of red blood cells can lead to anemia, a condition when oxygen can’t reach the body's tissues, making a person feel tired and weak. The discovery could have major implications for future longer-term space travel.

"If you are on your way to Mars and...you can't keep up" with the need to produce all those extra red blood cells, "you could be in serious trouble," Trudel says to Harikrishnan Nair for Reuters.

In the study, researchers took breath and blood samples from 14 astronauts before their six-month stays on the International Space Station and collected blood from the astronauts up to a year after their spaceflight. The astronauts also took samples four times during their missions. The team measured the amounts of carbon monoxide within the breath samples because a molecule of carbon monoxide is produced every time a molecule of heme, a component of red blood cells, is destroyed, explains Nick Lavars for New Atlas.

Female Astronaut Anne McClain holding biomedical gear for study while on the International Space Station.
Astronaut Anne McClain holds biomedical gear for study while on the International Space Station. NASA

The results revealed that astronauts lost around 54 percent more red blood cells in space. While on Earth, our bodies create and destroy around 2 million red blood cells per second. But in space, astronauts lost 3 million red blood cells per second during their six-month missions. The scientists say the reason red blood cells are being destroyed is likely due to fluid shifts the astronauts' bodies undergo to adjust to their weightless environment and back again.

“These findings are spectacular, considering these measurements had never been made before and we had no idea if we were going to find anything,” says Trudel in a statement. “We were surprised and rewarded for our curiosity.”

While the astronauts were losing red blood cells faster, the team wasn’t able to determine if they were replacing them faster, too. They concluded that the astronaut's bodies produced more cells to make up for the loss, or more would have suffered from severe anemia.

"Thankfully, having fewer red blood cells in space isn't a problem when your body is weightless," says Trudel. "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."

Even when the astronauts returned to Earth, their “space anemia,” didn’t go away. Follow-up samples showed that their red blood cell counts slowly returned to normal within three to four months of their return. But samples collected a year later revealed that the rate of red blood cell destruction was still revved up—now around 30 percent above pre-spaceflight levels, according to Ashley Strickland for CNN.

To reduce the risk of anemia in space, the researchers suggest tweaking astronaut diets to better support their health needs. The finding is also important for non-astronauts, as commercial space flight becomes more popular.

“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,” says Trudel.