The first study in the world has revealed how space travel destroys red blood cells, causing a decrease in their count (hemolysis), known as space anemia. An analysis of 14 astronauts has shown that their bodies destroyed 54% more red blood cells in space than they would normally do on Earth, according to a study published in Nature Medicine (ref.).

“Space anemia has been consistently reported when astronauts have returned to Earth since the early space missions, but we didn’t know why” said lead author Dr. Guy Trudel, a rehabilitation physician and researcher at the Ottawa Hospital and a professor at the University of Ottawa. “Our study shows that upon arrival in space, more red blood cells are destroyed, and this continues throughout the astronaut’s mission”.

Space Anemia

Before this study, space anemia was thought to be a rapid adaptation to fluids that shifted to the upper part of the astronaut’s body upon arrival in space. Astronauts lose 10% of the fluid in their blood vessels in this way. Instead, Dr. Guy Trudel’s team found that space destroys red blood cells and is a primary effect of being in a vacuum, and not just related to fluid shifting.

A venous blood draw aboard the ISS
A venous blood draw aboard the ISS. Credits: NASA, ESA

They demonstrated this by directly measuring the destruction of red blood cells in 14 astronauts during their six-month space missions. On Earth, our bodies create and destroy 2 million red blood cells every second. The researchers found that astronauts destroyed 54% more red blood cells during the six months they were in space, or 3 million per second. These results were the same for both female and male astronauts.

Dr. Trudel’s team made this discovery thanks to techniques and methods developed to accurately measure red blood cell destruction. These methods were then adapted to collect samples aboard the International Space Station (ISS). In the laboratory at the University of Ottawa, they accurately measured tiny amounts of carbon monoxide in the astronauts’ breath samples. A molecule of carbon monoxide is produced every time a molecule of heme, the intense red pigment of red blood cells, is destroyed.

Consequences of this imbalance

Although the team did not directly measure red blood cell production, they presume that astronauts generated extra red blood cells to compensate for the cells lost. This can be confidently stated, otherwise the astronauts would have had serious health problems in space. “Fortunately, having fewer red blood cells in space is not a problem when your body is weightless” said Dr. Trudel. “But when you land 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 have landed and have to face gravity again”.

In this study, 5 out of 13 astronauts were clinically anemic when they landed. Researchers found that space-related anemia is reversible, with red blood cell levels progressively returning to normal three or four months after returning to Earth. The team repeated the same measurements a year after the astronauts’ return to Earth. Red blood cell destruction levels were still 30% above preflight levels. These results suggest possible structural changes during space presence that altered red blood cell control for up to a year after long-duration space missions.

Implications of the discovery

The discovery that space destroys red blood cells is of great importance. Firstly, the longer the space mission, the worse the anemia. This issue could have an impact on long missions to the Moon and Mars. In addition, it is unclear how long the body can maintain this high rate of destruction and production of red blood cells.

These results could also be applicable to life on Earth. As a rehabilitation physician, most of Dr. Trudel’s patients are anemic. In these long-term sick patients with reduced mobility, anemia hinders their ability to exercise and recover their red blood cell count. Dr. Trudel thinks that this mechanism on Earth may have characteristics in common with space anemia. His team will investigate this hypothesis during future studies conducted on Earth.

“If we can discover exactly what is causing this anemia, then there is a possibility to treat or prevent it, both for astronauts and for patients here on Earth” said Dr. Trudel. “This is the best description we have of red blood cell control in space and after return to Earth. These results are spectacular, considering that these measurements had never been made before and we had no idea if we would find anything. We were surprised and rewarded for our curiosity”.

Stefano Gallotta
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