Lead
"Always tired." "Can't concentrate." "Falls apart after PE." When a girl in upper elementary school starts having days like these — around the time her period begins — the easy explanation is "she's growing" or "she's tired from activities." Both may be true. But these are also classic symptoms of iron deficiency, and they can be present and accumulating while the standard school hemoglobin screening shows nothing unusual.
"Not anemic" and "iron is adequate" are not the same statement.
The Three Stages of Iron Deficiency — and the Invisible Zone
Iron deficiency progresses through stages.
The first: depleted iron stores — hemoglobin: the iron-containing protein in red blood cells that carries oxygen to tissues throughout the body (Hb) is still normal, but serum ferritin: a protein that stores iron in cells; blood levels reflect the body's total iron reserves (the marker of the body's stored iron) has dropped. The second: iron deficiency without anemia (IDNA) — Hb still normal, ferritin low, serum iron falling. The third: iron deficiency anemia — Hb falls below normal.
School-based anemia screening typically measures Hb only. The first two stages — which may be affecting energy, concentration, and athletic performance — progress while school screening results show "normal."
Iron deficiency's character is gradual influence, not sudden collapse. A ferritin value below 15 µg/L is widely used as a treatment threshold [1,2]. Research also suggests that fatigue and reduced performance can appear at ferritin levels below 20–30 µg/L — above the anemia threshold, but still functionally meaningful [5].
Menstruation and the Iron Loss Equation
Menstruation adds an estimated 0.5–1.0 mg/day of additional iron loss, averaged across the cycle [2]. Japan's Dietary Reference Intakes 2020 (issued by the Ministry of Health, Labour and Welfare, MHLW) set the recommended dietary allowance (RDA) for iron at 14.0 mg/day for menstruating girls aged 10–11 — a substantial increase from the 8.5 mg/day recommendation for pre-menarchal girls of the same age [9].
How much of that gets through diet in practice? Not enough, in many cases. A study of young Japanese women (Morishita et al., 2009) found a weak correlation between dietary iron intake and serum iron, suggesting that food records alone are a poor tool for evaluating actual iron status [7]. "She eats plenty of vegetables" is not a reliable reassurance.
Additional Risk for Athletically Active Girls
Girls engaged in sports or physically demanding activities face iron loss through routes beyond menstruation.
Foot-strike hemolysis: destruction of red blood cells caused by the repeated impact of feet striking the ground during running or jumping (red blood cell destruction from repetitive ground impact), iron lost in sweat, and the absorption-inhibiting effects of phytate: a compound found in whole grains and legumes that binds iron in the gut and reduces its absorption in whole grains are all documented contributors [4,5]. An observational cohort study of female university athletes in Japan (Sugimoto et al., 2024) found that 47% had IDNA using a ferritin threshold of 30 µg/L [3]. That figure comes from a university-age population, but the structural risk for girls who begin competitive sports in late elementary school is similar.
"Not anemic, therefore fine" can be wrong at every stage of this picture.
Dietary Iron: What Works, What Doesn't
Iron from food falls into two categories with very different absorption rates:
- **Heme iron: iron bound within hemoglobin and myoglobin in animal tissues, absorbed much more efficiently than plant-based iron (red meat, liver, clams): 15–35% absorption
- Non-heme iron (spinach, hijiki seaweed, legumes, tofu): 2–5% absorption
Non-heme iron absorption increases substantially when consumed alongside vitamin C. It is reduced by tannins (green tea, coffee) and can be impaired by excess calcium competing at the absorption site.
The practical implication: what iron is eaten alongside matters as much as how much iron is eaten. Drinking green tea with meals — a common habit in Japan — reduces iron absorption; shifting it to 30 minutes after eating can make a measurable difference over time.
When to Seek Evaluation
When a girl who has started menstruating shows persistent fatigue, difficulty concentrating, or declining sports performance, asking a primary care physician for both Hb and ferritin is a reasonable step. Ferritin is a standard laboratory test that is generally covered by health insurance. The entry point is simply: "Can we test ferritin as well?" If iron deficiency is found early — at the IDNA stage rather than the anemia stage — options for intervention are broader.
What to Do Starting Now
- Know that ferritin exists as a test, separate from the Hb screen. If post-menarchal "general malaise" persists, asking a physician to check ferritin alongside Hb gives a fuller picture. "She's not anemic" should not end the inquiry.
- Build iron-rich foods into the weekly routine, not every meal. Red meat (beef, chicken liver), clams, tofu, spinach. "Reliably present three or four times a week" is more sustainable than attempting complete optimization every day.
- Shift green tea away from mealtimes. This alone, sustained over months, may improve actual iron uptake from diet.
Summary
Iron deficiency does not announce itself by collapse. It erodes quietly — fatigue, difficulty concentrating, reduced athletic performance — while hemoglobin levels remain technically normal. Girls who have begun menstruating are at structurally elevated risk; girls who are also active in sports face additional pathways of loss. Knowing that ferritin measures something Hb does not, and asking for it when the pattern warrants it, is the low-cost intervention that makes the invisible visible.
References
- Kazal LA Jr. Iron deficiency anemia in infancy, childhood, and adolescence. StatPearls. 2023. PMC: PMC10440944.
- Sachdev HPS, et al. Time to pay attention to anemia in female adolescents. Lancet Reg Health Southeast Asia. 2021;1:100006. PMC: PMC7873386.
- Sugimoto M, et al. Prevalence of iron-deficient but non-anemic university athletes in Japan: an observational cohort study. BMC Sports Sci Med Rehabil. 2024;16(1):11. doi:10.1186/s13102-024-00801-5. PMID: 38018828.
- Peeling P, et al. Athletic induced iron deficiency: new insights into the role of inflammation, cytokines and hormones. Eur J Appl Physiol. 2008;103(4):381–391. doi:10.1007/s00421-008-0726-6. PMID: 18365240.
- Morán M, et al. Iron and the female athlete: a review of dietary treatment methods for improving iron status and exercise performance. Open Access J Sports Med. 2015;6:177–195. doi:10.2147/OAJSM.S60288. PMC: PMC4596414.
- Sato T, et al. Iron deficiency prevention and dietary habits among elite female university athletes in Japan. Nutrients. 2025. PMC: PMC12299964.
- Morishita M, et al. Iron intake does not significantly correlate with iron deficiency among young Japanese women: a cross-sectional study. Eur J Clin Nutr. 2009;63(7):932–934. doi:10.1038/ejcn.2009.21. PMID: 19063766.
- Morán M, et al. Iron deficiency, supplementation, and sports performance in female athletes: a systematic review. Front Nutr. 2024. doi:10.3389/fnut.2024.1429137. PMID: 39536912.
- Ministry of Health, Labour and Welfare, Japan. Dietary Reference Intakes for Japanese 2020. https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/kenkou/eiyou/syokuji_kijyun.html