Hematological Micronutrients And Associations With Skeletal Health During Marine Officer Candidates School

Changes in micronutrients, including vitamin D and iron, have been observed during military training but are often assessed within a single sex and in isolation. The integral role of vitamin D in maintaining calcium homeostasis and musculoskeletal health is well understood, however, whether iron deficiency affects bone metabolism independently is not. Further, the reciprocal relationship between iron and vitamin D in men and women undergoing the same arduous training and how that may affect the skeleton has yet to be studied. PURPOSE: To characterize sex-specific hematological and nutritional status of men and women undergoing 10-weeks of Marine Officer Candidates School (OCS), determine interrelationships of biomarkers included, and examine how alterations to status affect skeletal health. METHODS: OCS candidates including 251 men and 52 women underwent two assessment time points, Pre (T1) and Post (T2). Iron (fe) status was measured via immunoenzymatic assays. Hepcidin was measured via Simple Plex ELLA. 25-hydroxyvitamin D (25(OH)D) was measured via mass spectrometry. Vitamin D and hematological status changes were assessed with two-way mixed-measures ANOVAs. Skeletal outcomes were assessed via pQCT at the distal metaphysis, mid- and proximal diaphysis. Pearson correlation (r) determined associations between hematological parameters. Multiple linear regression analysis was performed with bone parameters as the outcome variable and 25(OH)D, age, sex and BMI as explanatory variables. RESULTS: Decreased concentrations of 25(OH)D (8-10%), fe (20-35%) ferritin (18-37%), fe saturation (18-37%) and hepcidin (14-26%) were observed following training (all p < .001). Women exhibited greater 25(OH)D (p = .019) while men exhibited greater fe, ferritin and fe saturation (all p < .001). Change in fe saturation (r = -.125, p = .032) and baseline hepcidin (r = -.145, p = .032) were significantly correlated with change in 25(OH)D. Regression analysis revealed 25(OH)D significantly predicted 26.3% of the variation in cortical density and thickness (both p < .04). CONCLUSION: OCS deleteriously affected micronutrient status similarly in men and women. Results suggest an emerging association between vitamin D and fe status with plausible implications for operationally relevant outcomes. ONR N00014-20-C-2020