Prevalence and Impact of Anemia on Basic Trainees in the US Air Force

Iron-deficiency and iron-deficiency anemia are common conditions among girls and women in the USA, including those who compete in various sports, such as running, skiing, field hockey, crew, basketball, and softball [3, 8]. Given its association with work performance and endurance [7, 10], iron status is particularly important among athletes and others engaged in physically demanding professions, such as the armed forces [5, 7, 25]. In addition, iron-deficiency and iron-deficiency anemia have been associated with numerous adverse health outcomes, including musculoskeletal overuse injuries [16], impaired immune function [22], and psychological sequelae such as diminished cognitive performance [12] and depressed mood [21].

Iron supplementation in these populations may mitigate these conditions and improve performance. Among iron deficient females without anemia, iron supplementation has been shown to improve endurance [20], work capacity [9], and muscle function [2]. McClung and colleagues demonstrated improved vigor and physical performance, specifically running time, among female basic trainees with iron deficiency following iron supplementation [13, 14]. Similarly, iron supplementation of persons with iron-deficiency and iron-deficiency anemia yielded improvement in biochemical laboratory values and reduction of exercise-induced fatigue and increased work capacity [11].

In light of these and other studies, and acknowledging the continued debate regarding screening asymptomatic persons for anemia, Joint Base San Antonio (JBSA)-Lackland staff began screening all incoming US Air Force (USAF) basic trainees for anemia in July 2013. This study aimed to assess the results of this screening program: first, by a cross-sectional analysis to determine anemia prevalence, stratified by sex and severity; and second, by a retrospective cohort analysis to compare physical performance. Additionally, the study sought to determine the risks and relative risks of being discharged for anemic versus non-anemic women and men.

More than 25 % of females and 8 % of males were found to be anemic upon entrance to US Air Force basic military training. Both the anemic and non-anemic trainees had significant improvements in all components of their Air Force fitness assessment (1.5-mile run, push-ups, and sit-ups) from the beginning to the end of training. The discharge rate for anemic trainees was 9.0 % and for severely anemic trainees was 20.0 %, as compared to 5.7 % for those without anemia.

The high prevalence of anemia in this population is similar to that found in athletes but lower than the general US civilian population [3]. Although not obtained in this study, the prevalence of iron deficiency without anemia appears to be similar among female athletes and trainees and their civilian counterparts [3, 8]. Given increased iron losses via menstruation and lower iron intake than males [3, 12], it is not surprising that female basic trainees had a higher prevalence and greater severity of anemia as compared to male basic trainees.

Given discrepancies in discharge and delayed graduation rates and physical performance parameters between anemic and non-anemic trainees, as found in this study, anemia screening and early treatment may influence retention and physical performance during military training. Screening asymptomatic athletes and warriors for anemia remains controversial. The US Preventive Services Task Force [23] and National Athletic Trainers’ Association [4] do not currently recommend universal anemia screening of asymptomatic adult populations, and no other military services conduct universal screening. The Centers for Disease Control and Prevention, however, has recommended “screen[ing] all nonpregnant women for anemia every 5–10 years throughout their childbearing years,” beginning in adolescence [3]. Such discrepancies may reflect concerns regarding the criteria for an effective screening test [23] and issues with diagnostic accuracy: specifically, low serum iron and Hgb levels in well-trained athletes may either reflect true iron-deficiency anemia [13–15] or a physiologic increase in plasma volume secondary to rigorous physical training, a phenomenon known as “sports anemia” [18, 25]. A corollary argument is that identification and reversal of true anemia at baseline, prior to an intense period of military training, may help prevent exacerbation of anemia.

Additional benefits from screening could be surmised from this study. First, screening allowed for early identification of trainees with critically low Hgb values before commencing an intense exercise regimen. Second, since the majority of anemia cases were attributed to iron-deficiency, low cost treatment with oral iron supplementation was readily available. Third, anemic trainees were discouraged from participating in voluntary blood donation during week 7 of training; in the absence of baseline screening, some trainees with borderline anemia may have donated blood to the detriment of their physical performance. Fourth, three cases of leukemia and lymphoma were diagnosed because of the screening program; it is unclear, however, whether earlier diagnosis had an impact on morbidity or mortality in these cases.

Several drawbacks of screening were also identified. First, although screening tests were inexpensive, diagnostic workups for non-iron-deficient anemia cases were fiscally substantial. Additionally, since the Department of Defense Instruction, DoDI 6130.4 [6] stipulates “anemia that has not been permanently corrected with therapy” is disqualifiable from military service, medical providers were often perplexed by the appropriate military disposition of anemic trainees; this was particularly problematic given the time constraints of basic military training and the inability to demonstrate permanent correction.

Interestingly, improvements in 1.5-mile run time were less dramatic than improvements in sit-up counts among anemic trainees. Overall, anemic female and male trainees had longer average run times, fewer push-ups, and fewer sit-ups than non-anemic trainees at the beginning of training, with persistence of the statistical difference through the end of training, aside from final male sit-up values. However, run-times were more discrepant at the completion of basic training than were push-ups and sit-ups for both genders. This may be related to the aerobic nature of running, which is dependent on efficient oxygen delivery and extraction, or it could be hypothesized that the anaerobic work of strength-based exercises may be more rapidly amenable to iron repletion. It has been noted that iron supplementation in both anemic [7] and non-anemic [11, 17] women with iron deficiency reduces blood lactate accumulation during exertion, which may explain the superior improvements in muscular endurance observed here. In addition to the treatment of anemic trainees, the relatively similar fitness levels between the anemic and non-anemic trainees at the end of training may be explained by the homogenizing effect of a common fitness program or an increased discharge rate among the least fit trainees.

Strengths of this study include a robust sample size, cohort design, access to multiple operationally significant outcomes, and minimal loss to follow-up in a closely tracked military trainee population. The most significant limitation is the lack of a control group (i.e., a group of trainees identified as anemic but not treated), which would determine the efficacy of the iron intervention. Other limitations include lack of iron panel data for all subjects, yielding an unclear picture of the underlying causes of anemia, the possibility of poor trainee adherence to recommended iron replacement regimens, variability of dietary iron intake among anemic and non-anemic trainees, and lack of follow-up Hgb values, especially given the evidence that iron status declines during military training [13, 14].

In conclusion, this study demonstrates that anemia is prevalent in the military basic training population, specifically among female trainees. The problems of iron-deficiency and anemia and their impact on physical fitness in this population may mirror those among female young adult athlete populations. Further studies are needed to explore the implications of anemia in military and athlete populations and to determine whether the benefits of universal screening outweigh the harms. Future efforts should aim to identify effective and safe countermeasures, including dietary interventions, for the treatment of anemia during military training.

No financial support was received for the conduct of this study or preparation of this manuscript.