Incidence of Anemia and Iron Deficiency in Strenuously Trained Adolescents: Results of a Longitudinal Follow-Up Study

Purpose: Combat soldiers have a higher prevalence of anemia than age- and gender-matched civilians. This may be caused by hemodilution, which is typical among athletes, or by reduced body iron stores. The aim of this study was to investigate the incidence of iron-deficiency anemia in recruits to the Israel Defense Force after 6 months of training. Methods: Blood was collected from recruits before training. After 6 months of follow-up, 153 paired blood samples were collected from the initial cohort. Total blood count and serum iron, transferrin, and ferritin were measured at both time points. Soluble transferrin receptor (sTfR) was measured in 119 of the paired samples and the sTfR/log ferritin ratio was calculated. Results: At recruitment, mean hemoglobin concentration was 14.7 ± .9 g/dl. Iron-transferrin saturation was 34.1% ± 13.6%, and mean ferritin concentration was 53.6 ± 33.2 ng/ml. Anemia prevalence (Hb <14 g/dl) was 17.6%, and 14.9% of participants were iron-deficient (ferritin <22 mg/dl). At 6 months, 50.3% of the cohort was anemic, and 27.3% demonstrated iron-store depletion. Paired analysis showed an average reduction of .83 g/dl in hemoglobin (p < .001), and of 9.8 mg/dl in ferritin (p < .001). sTfR increased from 1.9 to 2.1 mg/dl (p < .003) among recruits who became anemic. Half of the recruits experienced mild anemia after 6 months of training. Iron store depletion was observed among 24.5% of the cohort after training, as opposed to 15% at recruitment. Overall, these changes were not accompanied by a significant increase in sTfR, but among the subset of anemic subjects, there was a slight increase in index value. Conclusions: In half of the cases, new-onset anemia was attributable to iron deficiency, and in the remainder, to hemodilution.