Hemolysis contributes to anemia during long-duration space flight

Abstract

Anemia in astronauts has been noted since the first space missions, but the mechanisms contributing to anemia in space flight have remained unclear. Here, we show that space flight is associated with persistently increased levels of products of hemoglobin degradation, carbon monoxide in alveolar air and iron in serum, in 14 astronauts throughout their 6-month missions onboard the International Space Station. One year after landing, erythrocytic effects persisted, including increased levels of hemolysis, reticulocytosis and hemoglobin. These findings suggest that the destruction of red blood cells, termed hemolysis, is a primary effect of microgravity in space flight and support the hypothesis that the anemia associated with space flight is a hemolytic condition that should be considered in the screening and monitoring of both astronauts and space tourists.

Fig. 1. Bone Marrow Adipose Reaction: Red Or White (MARROW) study design and outcomes.

a, Flow chart showing recruitment and samples harvested. SST, serum separator tube. b, Schematic showing the study design and planned sample collection. Astronauts recruited to the MARROW study performed serial measures at prespecified time points preflight, onboard the ISS and up to 1 year postflight. The average number of days (±s.d.) of sampling in relation to takeoff and landing are indicated. The interval between the last CO sampling in space and the first sampling on Earth after landing was 14 ± 5 days. Circles, CO measurements; squares, serum analytes (iron, transferrin percent saturation, ferritin, haptoglobin, bilirubin, C-reactive protein and EPO); diamonds, complete blood counts (CBCs) and reticulocytes. c, Time course of ambient air CO concentration onboard the ISS.

Fig. 2. Hemolysis and erythropoietic markers of astronauts preflight, onboard the ISS and postflight.

a, CO elimination. b–e, Serum iron concentrations (b), transferrin saturation (c), ferritin concentrations (d) and EPO concentrations (e). Data points and error bars represent mean values with ±95% CIs. Shaded areas represent data from ISS samples. f,g, Percentage of reticulocytes (f) and hemoglobin concentrations (g). The center line in the box plots represents the median, the upper limit of the box plots represents the third quartile (75th percentile), the lower limit of the box plots represents the first quartile (25th percentile), the upper whisker is the maximum value of the data that are within 1.5 times the interquartile range over the 75th percentile and the lower whisker is the minimum value of the data that are within 1.5 times the interquartile range under the 25th percentile. N = 14 astronauts who provided individual samples at five, eight or nine independent time points according to the outcome.