Our blood doesn’t like space: astronauts destroy too many red blood cells

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A stay in space is not without consequence on the blood of the astronauts. The effect of microgravity is an accelerated destruction of red blood cells in their blood.

What happens in the blood of astronauts who stay in space? Unsurprisingly, the effects are not very positive. Space travel helps destroy more red blood cells, say a team of scientists in Nature Medicine January 14, 2021. Their study is relayed by the University of Ottawa.

Since the very first space missions, we know that anemia, that is to say an abnormal drop in the level of hemoglobin (present in red blood cells) in the blood, can occur in astronauts. Normally, new red blood cells are created every day by the body, specifically by the bone marrow, to replace those that are destroyed. In the event of anemia, we find either that the production of red blood cells is insufficient, or that the red blood cells are well produced, but destroyed too much.

The blood of 14 astronauts on a mission to the ISS analyzed

Corn ” mechanisms contributing to anemia in spaceflight remained unclear “, note these scientists. This is why they undertook to measure markers of hemolysis (the destruction of red blood cells, a normal phenomenon as long as the destruction is not accelerated), in breath and blood samples from several astronauts. . They were on 6-month missions aboard the International Space Station. Samples were taken before the flight, 4 times during the mission and up to a year later, from 14 astronauts (11 men and 3 women). All of this happened between 2015 and 2020, as part of the MARROW experiment.

Thomas Pesquet inserting blood collection tubes from the MARROW experiment into a freezer on board the ISS in 2016. // Source: Nasa (cropped photo)

Results : ” spaceflight is associated with consistently increased levels of hemoglobin breakdown products “. Put more simply, this means that the excessive destruction of red blood cells (or haemolysis) would indeed be an effect caused by the fact of remaining in space – we speak more precisely of microgravity in the ISS. In these 14 astronauts, the scientists were able to observe that their bodies destroyed 54% more red blood cells in space, compared to what would normally happen on Earth.

  • On Earth, the human body creates and destroys 2 million red blood cells every second,
  • In the ISS, the body of these astronauts destroyed 3 million every second.

The scientists could not directly measure the production of red blood cells: what they quantified was the amount of carbon monoxide in the samples. A molecule of this type is created each time a molecule of heme (the red pigment of blood cells, specifies the press release) is destroyed. The researchers couldn’t verify whether the astronauts produced enough extra red blood cells to compensate for the destroyed cells, but it seems likely since they did not develop severe anemia.

Running out of red blood cells is especially a problem on landing

As these scientists explain, having fewer red blood cells is not necessarily a problem in weightlessness. It becomes so when landing on Earth (and certainly on other planets or moons) when the person finds himself again confronted with gravity. One could therefore imagine that this would have an impact after the astronauts land on the Moon or Mars, for example. And the longer the mission, the greater the risk of anemia.

On Earth, it was found that the phenomenon was reversible: 3 to 4 months after their return to our planet, the astronauts gradually returned to more normal levels of red blood cells. But this does not prevent longer-term effects: one year after the flight, the destruction of blood cells was still greater than 30%, compared to the level before the flight.

Look at the world from space

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