Time course for ferritin decay at 3800 m : Influence of biological sex

Sojourn to high altitude (HA) increases iron demand through hypoxia-induced erythropoiesis. Females have higher baseline iron requirements than males and may be more prone to iron deficiency at HA, yet previous studies examining ascent and iron were limited to small female sample sizes and limited temporal measures. To expand on past findings and assess sex differences in the Δferritin over 11 days at HA with ad libitum food availability, blood samples were obtained at sea-level and on days 2-4, 5-7, and 11 at HA in 27 (13 female) healthy volunteers. Using linear mixed modelling and Pearson’s correlations, we tested the hypotheses that at altitude ferritin would a) be lower in females at all timepoints, b) decrease similarly between sexes despite ad libitum energy and iron intake, and c) be inversely related to elevations in hemoglobin. A day*sex interaction (p < 0.01) revealed a steeper slope of ferritin decay in males (β = −3.74 μg/L/day) than females (β = −1.44 μg/L/day). Despite this observation, ferritin remained consistently ~70% lower in females across timepoints. By day 11 at HA, 6 out of 13 females were iron deficient (ferritin < 12 μg/L), with no iron deficiency (ferritin < 15 μg/L) occurring in males. The reductions in ferritin at HA were strongly related to elevations in hemoglobin in females (r = −0.79; p < 0.01) but not males (r = 0.28; p = 0.37). These data indicate that at 3800 m, despite ad libitum food availability, females are at a greater risk of iron deficiency, and ferritin is related to elevations in hemoglobin in females. Iron supplementation should be considered for females traveling and working at high altitude.