A world-first study has revealed how space travel can cause lower red blood
cell counts, known as space anemia. Analysis of 14 astronauts showed their
bodies destroyed 54 percent more red blood cells in space than they normally
would on Earth, according to a study published in Nature Medicine.
"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 rehabilitation physician and researcher at The
Ottawa Hospital and professor at the University of Ottawa. "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 quick adaptation to
fluids shifting into the astronaut's upper body when they first arrived in
space. Astronauts lose 10 percent of the liquid in their blood vessels this
way. It was thought astronauts rapidly destroyed 10 percent of their red
blood cells to restore the balance, and that red blood cell control was back
to normal after 10 days in space.
Instead, Dr. Trudel's team found that the red blood cell destruction was a
primary effect of being in space, not just caused by fluid shifts. They
demonstrated this by directly measuring red blood cell destruction 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 were destroying 54 percent
more red blood cells during the six months they were in space, or 3 million
every second. These results were the same for both female and male
astronauts.
Dr. Trudel's team made this discovery thanks to techniques and methods they
developed to accurately measure red blood cell destruction. These methods
were then adapted to collect samples aboard the International Space Station.
At Dr. Trudel's lab at the University of Ottawa, they were able to precisely
measure the tiny amounts of carbon monoxide in the breath samples from
astronauts. One molecule of carbon monoxide is produced every time one
molecule of heme, the deep-red pigment in red blood cells, is destroyed.
While the team didn't measure red blood cell production directly, they
assume the astronauts generated extra red blood cells to compensate for the
cells they destroyed. Otherwise, the astronauts would end up with severe
anemia, and would have had major health problems in space.
"Thankfully, having fewer red blood cells in space isn't a problem when your
body is weightless," said Dr. 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."
In this study, five out of 13 astronauts were clinically anemic when they
landed—one of the 14 astronauts did not have blood drawn on landing. The
researchers saw that space-related anemia was reversible, with red blood
cells levels progressively returning to normal three to four months after
returning to Earth.
Interestingly, the team repeated the same measurements one year after
astronauts returned to Earth, and found that red blood cell destruction was
still 30 percent above preflight levels. These results suggest that
structural changes may have happened to the astronaut while they were in
space that changed red blood cell control for up to a year after
long-duration space missions.
The discovery that space travel increases red blood cell destruction has
several implications. First, it supports screening astronauts or space
tourists for existing blood or health conditions that are affected by
anemia. Second, a recent study by Dr. Trudel's team found that the longer
the space mission, the worse the anemia, which could impact long missions to
the Moon and Mars. Third, increased red blood cell production will require
an adapted diet for astronauts. And finally, it's unclear how long the body
can maintain this higher rate of destruction and production of red blood
cells.
These findings could also be applied to life on Earth. As a rehabilitation
physician, most of Dr. Trudel's patients are anemic after being very ill for
a long time with limited mobility, and anemia hinders their ability to
exercise and recover. Bedrest has been shown to cause anemia, but how it
does this is unknown. Dr. Trudel thinks the mechanism may be like space
anemia. His team will investigate this hypothesis during future bedrest
studies done on Earth.
"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," said Dr. Trudel.
These are the first published results from MARROW, a made-in-Ottawa
experiment looking at bone marrow health and blood production in space. The
project is funded by the Canadian Space Agency and led by Dr. Trudel.
"This is the best description we have of red blood cell control in space and
after return to Earth," said Dr. 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."
Reference:
Trudel, G et al, Hemolysis contributes to anemia during long-duration space
flight. Nat Med (2022).
DOI: 10.1038/s41591-021-01637-7