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Why do astronauts get "space anemia"? This study has an answer.

SpaceX Crew-3 heads to space
NASA's SpaceX Crew-3 astronauts headed to International Space Station 02:04

A new analysis has found that space travel can lower red blood cell counts, leading to a condition known as "space anemia." A collaboration between The University of Ottawa and the Ottawa Hospital examined the red blood cell counts of 14 astronauts who had been to space, and found that their bodies destroyed 54% more red blood cells in space than they did on Earth — providing an answer to long-held questions about the condition.

"Space anemia has consistently been reported when astronauts returned to Earth since the first space missions, but we didn't know why," said lead author Dr. Guy Trudel, a researcher at The Ottawa Hospital and professor at the University of Ottawa, in a press release. 

Prior to this study, space anemia was believed to be caused by a sudden shift of fluids into an astronaut's upper body when they first entered space, causing the loss of 10% of the liquid in their blood vessels. It was also believed that their bodies would quickly destroy 10% of their red blood cells to balance this shift, and red blood cell count would return to normal after 10 days in space, the release said. 

But the research team discovered that being in space was actually the cause of the red blood cell destruction by measuring the red blood cell counts of the 14 astronauts over six months in space. The researchers didn't measure red blood cell counts directly, but they used a measurement of carbon monoxide — which is released when a part of a red blood cell is destroyed — as a proxy. 

On Earth, human bodies create and kill 2 million red blood cells every second — but in space, they destroy 3 million every second, the researchers said. 

"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," Trudel continued. 

Both male and female astronauts experienced the same red blood cell destruction, and five of 13 astronauts were clinically anemic upon landing, the researchers said in the release. One astronaut did not have blood drawn upon landing.

Astronaut Tim Peake's first blood draw completed in space. The sample was taken as part of the MARROW experiment. NASA

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

After the astronauts returned to Earth, it took three to four months for red blood cell counts to return to normal — but the scientists found that a year after landing, red blood cell death was still 30% higher than it was before the space mission.

"This is the best description we have of red blood cell control in space and after return to Earth," said Trudel. "These findings are spectacular, considering these measurements had never been made before and we had no idea if we were going to find anything. We were surprised and rewarded for our curiosity."

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