According to a study featured in the journal BMC Hematology, although space flight anemia is widely recognized the phenomenon, it may not be a significant concern during long-term space missions.

Spaceflight anemia is the depletion of circulating red blood cells (RBCs) during time spent in space. “There is an idea of 'space anemia' that is associated with space flight. However, this is based on blood samples from astronauts collected after flight, which may be influenced by numerous factors, for example, the stress of landing and re-adaptation to conditions on Earth,” said Dr. Richard Simpson; Associate professor at The University of Arizona and the University of Houston.

“The study, led by Dr. Brian Crucian at NASA Johnson Space Center, living, whole blood samples were collected during spaceflight and returned to earth for analysis. This unique sample allowed us to track hematological parameters such as concentrations of red blood cells (RBCs), hemoglobin or hematocrit — in astronauts on board the International Space Station during flight,” he added.

According to the study, concentrations of RBCs, platelets and the oxygen-carrying protein hemoglobin, as well as the hematocrit level, elevates during space flight. Even though astronauts' bodies acclimatize to microgravity after few days of flight, the RBC concentrations and hematocrit remains at higher levels.

The researchers studied the changes in the blood components occurred during space flight by analyzing the blood samples of 31 astronauts (6 women; 25 men) who spent up to six months on the International Space Station (ISS). Blood samples collection was made at 180 and 45 days before the mission, an in-flight collection made during first two weeks as well as at 3 and six months of space flight and sent back to earth within 48 hours of collection. Blood was also collected at 3–8 hours and 30 days after their arrival.

Researchers noted that the changes in the blood components observed in the in-flight blood samples might be due to the 48-hour processing delay between sample collection and analysis. The researchers also found noticeable changes in hematocrit level with the increased levels by 12.2%, 12.2% and 10.0% at early, mid, and late time points during space flight compared to preflight levels.

Whereas in reference samples collected on earth from non-astronauts found with only 4.7% increase in hematocrit after the 48-hour processing delay. When the researchers compared pre-flight and post-flight samples, they could find similar blood parameters in both.

Dr. Simpson concluded that the study could not specify the presence of significant anemia, but it must be elucidated in the context of astronaut’s plasma volume during flight. As there could find the reduction in the plasma volume in in-flight samples, but it's not been analyzed in long-term missions. “To fully interpret the changes to RBC, hematocrit and other parameters observed in this study, further research into plasma volume during long space missions is needed. This will be addressed in a separate ongoing NASA investigation.”