(PTFS12-03-23) Iron Metabolism in Spaceflight-analogs

Objectives: Nutrition and nutritional status are key components to the health and performance of astronauts and thus, to mission success. Adaptation to weightlessness results in a contraction of blood volume and a subsequent increase in tissue iron stores. Increased iron stores during spaceflight can be a concern given the association of excess iron stores with oxidative stress and physiological impacts such as bone loss. Ground analogs, including closed-chamber studies, are used to simulate elements of spaceflight on Earth.

Methods: We report here findings from a study performed in the Human Exploration Research Analog (HERA) habitat at the NASA Johnson Space Center. Sixteen subjects (6 women and 10 men) participated in 45-day missions during which blood samples were collected to determine iron and hematological status. Baseline values were averaged from two pre-mission timepoints (MD-15 and MD-10), whereas in-mission values are averages across MD5, MD26, and MD43 (MD = mission day). Results were also compared with previous closed-chamber studies and other spaceflight analogs (e.g., bed rest, dry immersion, hyperbaric saturation diving) and with data collected during space flight.

Results: In HERA subjects, hemoglobin (13 ± 1 g/dL) and hematocrit (39 ± 4 %) decreased by 6% from baseline (14 ± 1 g/dL and 42 ± 4 %, respectively), which was a change in the opposite direction when compared to bed rest subjects (increased 5% from baseline after 28 days). Regarding iron stores, reflected by serum ferritin, bed rest led to similar directional changes as spaceflight (19% and 28% increases for 28-d bed rest and 180-d spaceflight, respectively), while ferritin decreased 22% in HERA (dropping from 63 ng/mL to 49 ng/mL). Iron status in saturation dive studies most closely mimicked that of spaceflight.

Conclusions: While we are still assessing the cause of these changes, stress is one possible explanation for a decrease in circulating erythrocytes, but further studies measuring erythropoietin and other factors are necessary to better understand these effects. These findings provide insight into variation in physiological changes that take place under extreme environments which can inform recommendations for testing to be included on future space exploration missions.

Funding Sources: This work was funded by the NASA Human Research Program’s Human Health Countermeasures Element.