Longitudinal Declines in Iron Status in Female and Male US Army Recruits During Unaccustomed Military Training

Objectives: Exercise-induced inflammation may contribute to the decline in iron status frequently observed in physically active populations, which can negatively impact physical and cognitive performance. A challenge with assessing iron status is the confounding effect of inflammation on iron status indicators, including ferritin, the primary circulating indicator of iron storage. This study aimed to assess iron status while accounting for inflammation in military recruits across a period of unaccustomed physical training, 8-weeks of US Army Basic Combat Training (BCT). Methods: Indicators of iron status [ferritin, transferrin saturation (TSAT)], anemia [hemoglobin (Hb), hematocrit (Hct)], and inflammation [C-reactive protein (CRP)] were measured in fasted morning blood samples from females (n = 537, mean ± SD age = 20.7 ± 3.8 y) and males (n = 1077, 21.1 ± 3.9 y) at the start and end of 8 weeks of BCT. Ferritin was adjusted for CRP using the BRINDA method. Effects of time, sex, and time*sex interactions were assessed with two-way repeated measures ANOVAs. Data are medians (IQRs). Significance was set at p < 0.05. Results: BCT decreased iron status in females and males, indicated by reduced ferritin [females: 30.5 (17.1, 50.0) to 21.0 (11.9, 34.4) ng/mL; males: 112 (76.4, 162) to 73.0 (49.1, 114) ng/mL; p-time < 0.001, p-sex < 0.001, p-time*sex = 0.054] and reduced TSAT (p-time < 0.001, p-sex < 0.001, p-time*sex = 0.99). Both Hb and Hct increased with BCT (p < 0.001 for all). CRP decreased across BCT [females: 2.94 (1.27, 6.72) to 1.92 (0.83, 4.48) mg/L; males: 3.48 (1.43, 8.29) to 1.85 (0.87, 1.85) mg/L; p-time < 0.001, p-sex = 0.047, p-time*sex = 0.054]. Ferritin was lower after adjusting for CRP but still declined across BCT [females: 19.7 (10.6, 33.0) to 14.9 (8.5, 23.4) ng/mL; males: 65.7 (44.2, 96.2) to 50.2 (32.6, 50.2) ng/mL; p-time < 0.001, p-sex < 0.001, p-time*sex = 0.45]. Conclusions: Iron status declined during BCT, regardless of whether ferritin was adjusted for CRP. Reduced iron status and increased Hb and Hct suggest that a decline in iron storage supports increased erythropoiesis with unaccustomed physical training. Further research is necessary to determine the functional impact of declines in iron status without anemia. Funding Sources: Supported by USAMRDC; views are not official USARIEM, US Army, DoD, or government policy.