A study has uncovered what is behind the well-known phenomenon of “anemia” in astronauts: During stays in weightlessness, the loss of red blood cells far exceeds the normal level and is apparently only compensated to a certain extent. Space anemia will subside after landing, but the underlying effect will be felt for at least a year. The results are therefore of significance for space travel. In addition, research into space anemia may shed light on Earth versions of anemia, the scientists say.
Gravity is no longer tugging at the body and suddenly everything inside is floating: It seems almost astonishing that humans can cope with the unnatural conditions of space travel at all. However, as numerous studies have shown, there are definitely some critical effects and health risks. It has long been known that the blood of astronauts changes: since the first space missions, anemia has been repeatedly reported when astronauts return to earth. This is a reduction in the level of the oxygen-carrying cells in the blood – the erythrocytes.
What are the underlying effects?
The cause of space anemia has remained a mystery until now. Specifically, it was previously unclear whether lower production or increased breakdown of blood cells is the cause, when the effects occur and how long they last. Researchers led by Guy Trudel from the University of Ottawa investigated these questions as part of the MARROW project, which is dedicated to studying bone marrow health and blood production in space. The investigation data for the current study was provided by eleven male and three female astronauts who had spent an average of 167 days on the International Space Station ISS.
In their study, the researchers specifically investigated the suspicion that increased breakdown of red blood cells forms the basis of space anemia. As they explain, an enormous turnover of these blood cells is naturally constantly going on in the human body: of the body’s total of up to 30 trillion erythrocytes, around two million are destroyed every second – corresponding quantities are therefore reproduced in the bone marrow. The scientists investigated how many red blood cells are broken down in astronauts in space by detecting carbon monoxide in the air they breathe. As they explain, a molecule of this gas is created each time a heme is destroyed. This is the compound that gives blood cells their color and is involved in their ability to carry oxygen. The carbon monoxide content of the breathing air thus enables conclusions to be drawn about the breakdown rate of the erythrocytes in the body.
In this way, the team has now been able to document that a significantly increased dissolution of red blood cells occurs as soon as astronauts enter weightlessness. In concrete terms, it was found that around 54 percent more erythrocytes are destroyed than usual – i.e. around three million per second. While the researchers didn’t measure the production rate of red blood cells directly, it seems clear that astronauts’ bodies upregulate their formation. Otherwise, they would suffer from severe anemia and face serious health problems in space, the scientists explain. However, the increased loss in space is apparently only partially compensated for: the astronauts were classified as clinically anemic on landing, according to the investigations.
“Fortunately, when the body is weightless, the reduced red blood cell count caused by the effect isn’t an issue in space,” says Trudel. “The effects of anemia aren’t felt until you have to deal with gravity again. When landing on Earth and possibly on other planets or moons, this form of anemia can therefore impair energy, endurance and strength and thus jeopardize mission objectives,” says the scientist.
However, the space-related anemia is reversible, as further investigations confirmed: the number of red blood cells gradually returned to normal three to four months after returning to earth. But that was apparently only partly due to the decline in the increased breakdown rate: A year after the astronauts returned to Earth, the team found that red blood cell destruction was still 30 percent above pre-flight levels. However, the cause of the increased erythrocyte decay remains unclear and should now be clarified by further investigations, the researchers emphasize. However, the fundamentals are already becoming apparent: astronauts experience physical changes that continue to shape the system for breaking down and building up red blood cells for up to a year after long space missions, the scientists sum up.
Significance for space travel and medicine
They say the results could have multiple meanings: It now seems increasingly important that astronauts or space tourists are screened for pre-launch problems that could be linked to anemia. In addition, the astronauts’ diet may need to be adjusted to accommodate the increased production of red blood cells. Above all, however, the question arises as to how long the body can easily keep up with the higher rate of destruction and production in the red blood cells. This seems particularly important with regard to planned long-term stays in space – for example when traveling to Mars.
The new findings could also shed light on the causes of certain forms of anemia on Earth, the researchers conclude. It is known that long periods of bed rest can trigger anemia, which affects the ability of sufferers to recover and regain mobility. In this case, too, the causes are still unclear. Trudel suspects that similar mechanisms may underlie this form of anemia and the space version. The team now wants to follow this lead as well. “If we can find out exactly what causes these anemias, then there is a chance to treat or prevent them, both in astronauts and in patients on Earth,” Trudel said.
Source: Tim Peake, Article: Nature Medicine, doi: 10.1038/s41591-021-01637-7