Space anemia poses a significant risk to deconditioning, and should be considered as space tourism becomes more popular and available, according to a paper published in the American Journal of Hematology.1

Space travel–related anemia has been a concern for the past 60 years, though conflicting data have prevented researchers from determining, with certainty, that being in space can directly lead to the condition. Researchers determined that evaluating hemoglobin (Hb) concentrations and red blood cell (RBC) mass within 7 days of returning to Earth from space would, however, be sufficient for determining any link.

For this study, the authors evaluated data recorded in the National Aeronautics and Space Administration’s Lyndon B. Johnson Space Center’s system, which contains records for all astronauts since the program’s inception, to determine any causal relationship between space travel and changes in Hb concentrations.

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Two datasets were included, the first of which contained records from 711 mission-astronauts with 1962 Hb measurements and 721 mission-astronauts with 17,336 Hb measurements. All data were compared with those from control records taken at the time of each mission.

Forty-eight percent of astronauts were anemic when they returned to Earth after space travel. Longer trips to space also appeared to require more recovery time after the journey than did shorter trips, with Hb levels returning to normal after 49 days for trips of 11.5 to 145 days vs 24 days for trips of a mean of 5.4 days.

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Astronauts whose trips lasted 5.4 days, 11.5 days, and 145 days had Hb decrements of -0.61 g/dL (4%), -0.82 g/dL (5%), and -1.66 g/dL (11%), respectively.

“We characterized space anemia, its dose-response relationship with exposure to space as well as longitudinal effects,” the authors wrote. “Whether acute space anemia will turn into chronic anemia depends critically on the duration of exposure to space.”


Trudel G, Shafer J, Laneuville O, Ramsay T. Characterizing the effect of exposure to microgravity on anemia: more space is worse. Am J Hematol. 2020;95(3):267-273.