In space, astronauts experienced 3 million red blood cells destroyed per second, resulting in a loss of 54% more cells than people on Earth experience, according to a new study.

Lower red blood cell counts in astronauts is known as space anemia.

"Space anemia has consistently been reported when astronauts returned to Earth since the first space missions, but we didn't know why," said study author Dr.

Trudel and his team discovered a surprising result -- the space environment is the actual culprit.

"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," he said.

The research team developed ways to measure red blood cell destruction, including measuring the amounts of carbon monoxide detected in breath samples from the astronauts.

One of the astronauts did not have a blood draw after landing.

Follow-up samples taken from the astronauts showed that space anemia is reversible because their red blood cell counts progressively returned to normal between three to four months after their return.

However, samples collected a year after the astronauts landed on Earth showed that the rate of red blood cell destruction was still increased, about 30% above what they experienced before their spaceflight.

The researchers believe this suggests that long-duration space missions could result in structural changes that impact red blood cells.

The findings are the first results published from MARROW, an experiment that examines bone marrow health and blood production when astronauts are in space.

A previous study by Trudel and his team also revealed that longer space missions worsen anemia.

For now, it's uncertain how long the human body can support an increased rate of both destruction and production of red blood cells.