Abstract
his study investigated the percentage of iron deficiency anemia (IDA) and iron deficiency (ID) among 71 elite female athletes at a Japanese university and assessed their dietary habits. IDA was identified in 9.9% (n= 7) of participants, and only 22.5% (n= 16) self-reported dietary practices aimed at preventing or managing ID/IDA. Notably, 52.1% (n= 37) of the athletes exhibited IDA or ID but lacked an appropriate dietary approach. Moreover, even among those who reported an intentional dietary approach to the prevention or management of ID/IDA, the intake of iron- and vitamin C-rich foods was insufficient, limiting the effectiveness of their efforts. These findings highlight a gap between awareness and effective practice, indicating that many female athletes in Japan, despite being at elevated risk, do not follow evidence-based dietary strategies for preventing or treating ID/IDA. Targeted nutritional education and routine screening of iron status are
ID/IDA, the intake of iron- and vitamin C-rich foods was insufficient, limiting the effectiveness of their efforts. These findings highlight a gap between awareness and effective practice, indicating that many female athletes in Japan, despite being at elevated risk, do not follow evidence-based dietary strategies for preventing or treating ID/IDA. Targeted nutritional education and routine screening of iron status are strongly recommended for this population. Keywords:anemia; female athlete; eating habits; hemoglobin 1. Introduction Iron is a component of all living cells and is recognized as an essential element for maintaining health. It is involved in various biochemical reactions, including oxygen transport (as a component of hemoglobin), ATP production, DNA synthesis, and electron transfer [1,2]. Most of the body’s iron (approximately 65%) is found in hemoglobin, which is present in red blood cells. Other locations include myoglobin in the muscles, enzymes, cytochromes, reticuloendothelial system (RES) macrophages, and bone marrow. The stored portion is present in liver cells as ferritin [3,4]. Iron metabolism is among the most intricate processes within the human body, encompassing numerous organs and tissues, including the intestines, bone marrow, spleen, and liver [5]. Iron is efficiently stored through the body’s homeostasis mechanisms; however, iron deficiency may occur when intake falls below physiological requirements or stores are depleted. Individuals considered to be at high risk for iron deficiency include premenopausal women; infants; elderly hospitalized patients who undergo frequent blood draws for diagnostic purposes; individuals with Sports2025,13, 220 https://doi.org/10.3390/sports13070220
Sports2025,13, 220 2 of 12 gastrointestinal bleeding, malabsorption states, and/or gastric cancer; and those who have undergone gastrointestinal surgery [6]. Iron deficiency anemia (IDA) and iron deficiency (ID) are the most common mi- cronutrient disorders worldwide [7,8]. Iron is involved in multiple cellular functions and physiological systems, making it essential for human health. ID is a leading contributor to the global burden of disease, particularly affecting children, premenopausal women, and people living in low- and middle-income countries [9,10]. Additionally, IDA and ID are common nutrient deficiencies among athletes, especially in endurance-trained athletes [11], and ID is known to significantly contribute to reduced performance [11–13]. The iron requirements of athletes may be higher due to the increased erythropoietic drive caused by regular exercise. Moreover, increased iron losses (i.e., through the gastrointestinal tract, hematuria, and sweat) [14], poor dietary iron intake [15], foot strike hemolysis [16], exercise-induced inflammation [17], and environmental factors such as hypoxia may all influence iron metabolism in athletes [18]. In particular, female athletes are at risk for ID due to menstruation; thus, ID screening is widely recommended for all athletes [19–21]. In fact, women lose approximately 1 mg of iron per day during menstruation, which may be higher for heavy menstrual bleeding, where blood loss is estimated to be 5–6 times greater [22]. However, despite the importance of iron, ID remains highly prevalent, globally ranging between 9% and 60% in female athletes [23,24]. Low Hb concentrations can result in reduced oxygen (O2) transport to working muscles; this is the primary mechanism for reduced performance due to anemia. More specifically, these reduced performance outcomes include decreases in maximal O2con- sumption (VO2max) and aerobic power [19]. IDA can also significantly impact perfor- mance depending on its severity, whereas the impact of non-anemic iron deficiency (NAID; Hb≧12 g/dL and Ft < 30µg/L) is less clear, although some reports have investigated it [25]. One study evaluated the relationship between serum Ft and 2 km time trial performance among female collegiate rowers at the beginning of a competition season, with athletes with NAID having slower trial times compared to those with sufficient iron
of non-anemic iron deficiency (NAID; Hb≧12 g/dL and Ft < 30µg/L) is less clear, although some reports have investigated it [25]. One study evaluated the relationship between serum Ft and 2 km time trial performance among female collegiate rowers at the beginning of a competition season, with athletes with NAID having slower trial times compared to those with sufficient iron stores [26]. Moreover, several studies have demonstrated increased aerobic capacity indices after iron supplementation in female athletes [27,28], which implies that performance was affected by NAID. Oral iron supplementation is the first-line treatment for IDA and ID, and adequate iron intake is also paramount to their prevention [29]. Iron is available in many supple- mental forms to support the higher recommended dietary iron intake of female athletes. According to the Dietary Reference Intakes for Japanese (2020), the recommended dietary allowance for iron is 10.5 mg/day for women aged 18–49 years with menstruation [30]. In Japan, menstrual iron loss is estimated to be approximately 0.55 mg day, corresponding to approximately 15.5 mg per menstrual cycle. Premenopausal adult women need to account for the additional iron loss from menstruation [31]; thus, the reference nutrient intake for adult females in the UK is 14.8 mg/day [32], while the recommended dietary allowance in the US is set at 18 mg/day [33]. A strategic approach to iron ingestion (e.g., the timing of iron intake) could enhance iron absorption in this population, which has become a topic of interest for examining ID in athletes [34]. Athletes with ID are commonly recommended to take 60–120 mg/day of elemental iron given for 2 months, varying based on ID severity and individual tolerance from a gastrointestinal perspective [35,36]. In Japan, 100–200 mg/day is commonly pre- scribed for ID and IDA treatment [37]. However, some athletes stop taking medications due to significant gastrointestinal side effects [38]. Improvements in hematological biomarkers have been documented in response to iron supplementation in athletes with ID [23,39]. However, the effectiveness of iron supple-
IDA treatment [37]. However, some athletes stop taking medications due to significant gastrointestinal side effects [38]. Improvements in hematological biomarkers have been documented in response to iron supplementation in athletes with ID [23,39]. However, the effectiveness of iron supple-
Sports2025,13, 220 3 of 12 mentation on physical parameters beyond endurance performance and maximal aerobic capacity is unclear, which is particularly important in sports requiring substantial strength and power (e.g., weightlifting, American football). Thus, aside from iron supplementa- tion, consuming foods with high iron content (e.g., liver, eggs, red meat, fish, tofu, and spinach) is also important for preventing ID and IDA. It is also important to consume vitamin C, which promotes iron absorption. Moreover, avoiding iron absorption inhibitors, including tannins, calcium, oxalates, and phytic acid, can help prevent the reduction in iron bioavailability [40]. Although there are few studies on athletes with specific diets to prevent ID, further studies in this field are needed. In addition, no studies have examined the actual eating awareness and behavior of athletes with dietary habits specifically aimed at preventing IDA/ID. This study aimed to investigate IDA/ID percentages among female athletes in one elite Japanese university and clarify the dietary awareness, eating habits, and iron nutritional status of athletes who self-report having specific dietary habits at IDA/ID prevention. 2. Materials and Methods 2.1. Participants and the Survey Period A total of 71 female university athletes from competitive sports clubs (e.g., basketball, volleyball, swimming, soccer, and track and field) participated in this cross-sectional study between December 2022 and February 2023. Participants were recruited for the survey by the co-author in collaboration with team trainers. All 71 individuals provided informed consent before participation, resulting in a 100% response rate. Participants unable to undergo physical measurements on the day of the survey due to injury were eligible for exclusion; however, no participant met these exclusion criteria. The surveys were conducted during the training period. All teams competed at the national level in Japan (classified as Tier 3 competition) [41]. The participants were informed about the purpose, procedures, and potential risks of the study, and written informed consent was obtained in advance. Participation was voluntary, with the option to withdraw at any time. 2.2. Ethical Considerations This study was conducted per the Declaration of Helsinki [42] and the Ethical Guide- lines for Medical Research Involving Human Subjects (Ministry
competition) [41]. The participants were informed about the purpose, procedures, and potential risks of the study, and written informed consent was obtained in advance. Participation was voluntary, with the option to withdraw at any time. 2.2. Ethical Considerations This study was conducted per the Declaration of Helsinki [42] and the Ethical Guide- lines for Medical Research Involving Human Subjects (Ministry of Education, Culture, Sports, Science and Technology and Ministry of Health, Labor and Welfare 2017) [43]. The study protocol was reviewed and approved by the Institutional Review Board of Niigata University of Health and Welfare (approval number: 18831-220526). 2.3. Anthropometry Height (cm), body weight (kg), and body fat (%) were measured using a digital height meter (AD6400, A&D, Tokyo, Japan) or bioelectrical impedance method (InBody470, Inbody Japan, Tokyo, Japan). The body mass index (BMI) was calculated as body weight (kg)/height (m 2 ). 2.4. Methods and the Dietary Survey Two questionnaires assessed participants’ dietary habits. First, a 12-item survey examined the weekly frequency of food intake behaviors (maximum 7 days/week). Items included meal consumption frequency (e.g., breakfast), staple foods, major food groups (e.g., vegetables, meat, dairy), and snack intake [44]. The Brief Self-Administered Diet History Questionnaire (BDHQ) [45,46] was used to estimate energy and nutrient intake. This self-report tool assesses the intake frequency of 58 food and beverage items over the previous month. Participants respond using a
Sports2025,13, 220 4 of 12 seven-point scale to indicate how often they consumed each item [47]. Kobayashi et al. reported that the BDHQ has acceptable validity for ranking nutrient and food group intake among Japanese adults [45]. In particular, they found a Pearson correlation coefficient of 0.62 between iron intake estimated by the BDHQ and that from 16-day dietary records, supporting the BDHQ’s reliability in assessing iron intake. Participants used food models of typical Japanese rice bowl sizes (150–350 g) and a rice ball (100 g) to improve the accuracy of rice intake estimation. This helped address common under- or overestimation, especially among athletes. In the BDHQ, one serving of rice is assumed to be 150 g. The completed questionnaires were returned by mail to Gender Medical Research Inc., where dietary data were analyzed using a standardized scoring algorithm. Two additional items were assessed via a questionnaire. First, participants were asked whether they usually followed a diet mindful of preventing or managing IDA or ID, with responses categorized as “yes” or “no.” Second, information regarding the product name, intake timing, and frequency of use was collected and added to the BDHQ result for those who reported dietary supplement use. Energy and nutrient intake were calculated per kg of body weight. Staff, such as coaches and trainers, were not present to ensure unbiased responses. Two registered dietitians were available to assist participants with the BDHQ and rice portion estimation. 2.5. Biochemical Tests Blood samples were collected via venipuncture in the morning, and each item was measured within 3 h after collection. Dietary and physical activity restrictions were not imposed. Red blood cell count (RBC), Hb, and hematocrit (Ht) were measured using a multi-parameter automated blood cell analyzer XR-1000 (Sysmex Corporation, Hyogo, Japan) with whole blood placed in an EDTA blood collection tube. Serum iron, unsaturated iron-binding capacity (UIBC), and serum Ft were measured using serum. The measure- ment equipment used was an automated analyzer LABOSPECT006 (Hitachi High-Tech Corporation, Tokyo, Japan). 2.6. Proportion of Subjects with Anemia and Iron Deficiency Stages Subjects were classified based on the staging classification of the Swiss
Japan) with whole blood placed in an EDTA blood collection tube. Serum iron, unsaturated iron-binding capacity (UIBC), and serum Ft were measured using serum. The measure- ment equipment used was an automated analyzer LABOSPECT006 (Hitachi High-Tech Corporation, Tokyo, Japan). 2.6. Proportion of Subjects with Anemia and Iron Deficiency Stages Subjects were classified based on the staging classification of the Swiss Society of Sports Medicine for anemia/ID as follows: normal (Hb≧12 g/dL and Ft≧30µg/L), NAID (Hb≧12 g/dL and Ft < 30µg/L), ID with microcytosis and hypochromia (IDMH, Hb≥12 g/dL, Ft < 30µg/L, MCH < 28 pg, MCV < 80 fL), IDA (Hb < 12 g/dL and Ft < 30µg/L), and non-iron deficiency anemia (NIDA, Hb < 12 g/dL and Ft≧30µg/L) [35]. 2.7. Statistical Analysis Data were analyzed using R (version 4.1.0.). Statistical analyses were conducted to compare two groups based on responses to the following question: “Do you consume a diet mindful of preventing or treating IDA daily?” An independent t-test was conducted to analyze differences in physical measurements, blood test results, and quantitative and qualitative food frequency questionnaire responses. Fisher’s exact test with Holm correction was applied to compare anemia prevalence according to dietary habits. The significance level was set atp< 0.05. 3. Results Table 20.2±1.0 years (mean±SD). Out of 71 participants, 16 (22.5%) had dietary habits aimed at preventing or treating ID, while 55 (77.5%) did not, and these groups had no differences in height, body mass, BMI, and body fat percentage. Regarding their sports clubs, the highest
Sports2025,13, 220 5 of 12 number of participants were part of the basketball club (n= 21), followed by volleyball (n= 16), swimming (n= 13), soccer (n= 12), and track and field (n= 9) (Table). Among athletes who followed dietary practices to prevent ID, the highest and lowest percentages were seen among soccer players (58.3%) and swimmers (7.7%), respectively. Table 1.Physical characteristics of female athletes grouped based on dietary habits. Dietary Practices to Prevent or Treat Iron Deficiency No Yes p-Value n= 55, 77.5% n= 16, 22.5% Age, year 20.2 ±1.0 20.2 ±1.1 0.939 Height, cm 164.8 ±5.6 162.8 ±5.8 0.227 Body Mass, kg 59.1 ±6.8 57.6 ±5.9 0.227 BMI, kg/m 2 21.8±1.9 21.7 ±1.0 0.893 Body Fat, % 22.8 ±4.7 22.8 ±3.8 0.994 Data are presented as the mean±SD. BMI, body mass index. Table 2.Sports clubs of female athletes grouped based on dietary habits. Use of Self-Reported Dietary Practices to Prevent or Treat Anemia Club No Yes n= 55, 77.5% n= 16, 22.5% Basketball 17 (30.9%) 4 (25.0%) Soccer 5 (9.1%) 7 (43.8%) Volleyball 14 (25.5%) 2 (12.5%) Track and field 7 (12.7%) 2 (12.5%) Swimming 12 (21.8%) 1 (6.3%) IDA was identified in 9.9% (n= 7) of the surveyed female college athletes. The proportion of athletes with normal iron nutritional status was the highest among basketball players (35.0%) and the lowest among volleyball players (17.6%) (Table). Table the percentage of anemia and ID stages according to the presence of dietary habits for preventing or treating anemia. The IDA rate was 18.8% (3/16) and 7.3% (4/55) in the athletes with dietary habits for preventing or treating anemia and those who did not follow a diet, respectively. Table 3.Anemia and stages of iron deficiency among female athletes grouped based on sports clubs. Club Normal NAID IDMH IDA NIDA Basketball 7 (35.0%) 11 (55.0%) 0 (0.0%) 2 (10.0%) 0 (0.0%) Soccer 5 (41.7%) 5 (41.7%) 0 (0.0%) 1 (8.3%) 1 (8.3%) Volleyball 3 (17.6%) 10 (58.8%) 0 (0.0%) 4 (23.5%) 0 (0.0%) Track and field 2 (22.2%) 7 (77.8%) 0 (0.0%) 0 (0.0%) 0 (0.0%) Swimming 4 (30.8%) 9 (69.2%) 0 (0.0%)
clubs. Club Normal NAID IDMH IDA NIDA Basketball 7 (35.0%) 11 (55.0%) 0 (0.0%) 2 (10.0%) 0 (0.0%) Soccer 5 (41.7%) 5 (41.7%) 0 (0.0%) 1 (8.3%) 1 (8.3%) Volleyball 3 (17.6%) 10 (58.8%) 0 (0.0%) 4 (23.5%) 0 (0.0%) Track and field 2 (22.2%) 7 (77.8%) 0 (0.0%) 0 (0.0%) 0 (0.0%) Swimming 4 (30.8%) 9 (69.2%) 0 (0.0%) 0 (0.0%) 0 (0.0%) NAID: non-anemic iron deficiency; IDMH: iron deficiency with microcytosis and hypochromia; IDA: iron deficiency anemia; NIDA: non-iron deficiency anemia without reduced serum ferritin. Table based on their dietary habits. Both Hb and Ht were significantly lower in the group with dietary practices to prevent ID than those who did not follow a diet (Hb: 12.6±0.9 vs. 13.1±0.9 g/dL,p< 0.034; Ht: 38.1%±2.2% vs. 39.8%±2.6%,p< 0.028). The remaining anemia-related parameters, such as MCV, MCH, MCHC, RBC, serum iron, and serum Ft, were similar between the two groups.
Sports2025,13, 220 6 of 12 Table 4.Iron deficiency stages among female athletes grouped based on dietary habits. Diagnosis Use of Self-Reported Dietary Practices to Prevent or Treat Anemia No Yes p-Value n= 55, 77.5% n= 16, 22.5% Normal 18 (32.7%) 3 (18.8%) 1.000 NAID 33 (60.0%) 9 (56.3%) IDMH 0 (0.0%) 0 (0.0%) IDA 4 (7.3%) 3 (18.8%) NIDA 0 (0.0%) 1 (6.3%) Fisher’s exact test (Holm-adjustedp-values). NAID: non-anemic iron deficiency, IDMH: iron deficiency with microcytosis and hypochromia, IDA: iron deficiency anemia. Table 5.Hematologic data and iron status of female athletes grouped based on dietary habits. Items Dietary Practices to Prevent or Treat Iron Deficiency No Yes p-Value n= 55, 77.5% n= 16, 22.5% Hb g/dL 13.1 ±0.92 12.6 ±0.89 0.034 Ht % 39.7 ±2.6 38.1 ±2.32 0.028 MCV fl 91.2 ±3.53 90.2 ±2.9 0.275 MCH pg 30.2 ±1.18 29.8 ±1.46 0.316 MCHC % 33.1 ±0.66 33 ±0.8 0.562 Serum iron µg/dL 97.0 ±32.2 77.4 ±34.7 0.062 RBC ×10 4 /µL 436±33 422 ±32 0.176 UIBC µg/dL 250 ±53 270 ±61 0.250 Serum Ft ng/mL 25.6 ±17.2 24.0 ±20.4 0.778 Data are presented as the mean±SD. Normal: Hb≧12 g/dL and Ft≧30µg/L. The qualitative food frequency survey results are shown in Table. Athletes who actively engaged in IDA prevention had a significantly greater frequency of abstaining from sweets and soft drinks compared to those who were not (4.13±2.34 vs.2.73±2.18 days per week,p= 0.049). The intake frequency of light-colored vegetables (e.g., cucumbers, cabbage, lettuce, etc.) was also significantly greater among athletes with dietary practices versus those without (5.34±1.05 vs. 4.67±1.54 days per week,p= 0.048). There were no significant differences between the two groups in the frequency of meat, fish, and egg intake and the frequency with which breakfast was eaten. Table 6.Qualitative food intake frequency survey results of female athletes grouped based on dietary habits. Dietary Practices to Prevent or Treat Iron Deficiency Number of Days Per Week No Yes p-Value n= 55, 77.5% n= 16, 22.5% Avoiding sweets and soft drinks (juice, etc.) 2.73±2.18 4.13 ±2.34 0.049 Eating 3 meals a day (breakfast, lunch, and dinner)5.16±1.99 5.88 ±1.36 0.118 Eating staple
Description
The study highlights dietary gaps in preventing iron deficiency among female athletes.