Prevalence of iron-deficient but non-anemic university athletes in Japan: an observational cohort study

Figures & data

Table 1. Participant characteristics.

Variables	Total (n = 126)	Male (n = 79)	Female (n = 47)
Age (years)	20 [19 ‒ 21]	20 [19 ‒ 21]	19 [19 ‒ 21]
Years of sports/athletics	13 [11 ‒ 15]	14 [12 ‒ 15]	12 [8 ‒ 15]
Affiliated club
Badminton	20 (16)	13 (16)	7 (15)
Baseball	21 (17)	21 (27)	0 (0)
Handball	20 (16)	0 (0)	20 (43)
Kendo	65 (52)	45 (57)	20 (43)
Height (cm)	171 [165 ‒ 177]	174 [171 ‒ 179]	163 [158 ‒ 166]
Body weight (kg)	72 [65 ‒ 80]	75 [69 ‒ 83]	62 [57 ‒ 66]
Body mass index (kg/m^2)	24.4 [23.2 ‒ 25.8]	24.6 [23.7 ‒ 26.1]	23.1 [21.8 ‒ 24.3]
Body fat percentage (%)^†	16.3 [12.7 ‒ 20.9]	14.3 [12.1 ‒ 17.3]	24.7 [22.0 ‒ 27.8]
History of anemia^†	7 (6)	1 (1)	6 (13)
Previous use of iron supplement^†	40 (32)	20 (26)	20 (44)
Food Frequency Questionnaire
Total energy intake (kcal/day)	2,151 [1,736 ‒ 2,707]	2,297 [1,842 ‒ 2,809]	1,916 [1,629 ‒ 2,322]
Iron intake (mg/day)	6.7 [5.0 ‒ 8.6]	7.2 [5.0 ‒ 8.8]	6.2 [5.0 ‒ 8.0]

Median [interquartile range] or number (percentage) are shown. ^† Missing data -total number (male/female); 21 (1/20), 3 (2/1) and 4 (3/1) in body fat percentage, history of anemia and previous use of iron supplement, respectively.

Table 2. Anemia and iron status.

Variables	Total (n = 126)	Male (n = 79)	Female (n = 47)
Anemia status
Prevalence of anemia*	0 (0)	0 (0)	0 (0)
RBC (×10^6/μL)	495 [454–522]	510 [493.5–540.5]	444 [425–471.5]
Hemoglobin (g/dL)	14.8 [13.8–15.5]	15.3 [14.75–15.85]	13.6 [12.65–14.1]
Hematocrit (%)	45.1 [42.8–47.4]	46.8 [44.8–48.35]	42.2 [39.9–44.15]
MCV (fL)	92 [90–94]	91 [89–93]	94 [92–96]
MCH (pg)	30.1 [29.2–30.7]	29.9 [29.2–30.4]	30.7 [29.7–31.05]
MCHC (g/dL)	32.6 [31.9–33.1]	32.8 [32.4–33.3]	32.1 [31.65–32.7]
Iron Status
Serum iron level (μg/dL)	89.5 [67–130]	93 [67–133]	88 [67–126]
TIBC (μg/dL)	338.5 [318–362]	331 [318.5–351]	347 [322–387.5]
Prevalence of hypoferritineamia −n (%, 95% CI)	22 (17, 11–25)	0 (0, 0–5)	22 (47, 32–62)
Ferritin (µg/L)	70 [31-]105]	94 [70–128]	35 [20-]49]
>100 and ≤ 300	40 (32)	38 (48)	2 (4)
>50 and ≤ 100	39 (31)	31 (39)	8 (17)
>30 and ≤ 50	25 (20)	10 (13)	15 (32)
>15 and ≤ 30	14 (11)	0 (0)	14 (30)
≤15	8 (6)	0 (0)	8 (17)

Median [interquartile range] or number (percentage) are shown. Abbreviations: RBC. red blood cell; MCV, mean corpuscular volume; MCH, mean corpuscular hemoglobin; MCHC, mean corpuscular hemoglobin concentration; TIBC, iron binding capacity. *Definition of anemia is accordance with WHO criteria.

Figure 1. Serum ferritin levels classified by sex and affiliated club.

Distribution of serum ferritin levels was shown after classifying by sex and the affiliated clubs. The line within box, box, whisker and dots indicate the median, interquartile range, 1.5 times the interquartile range and the outliers, respectively.

Table 3. Participant characteristics associated with hypoferritinemia in female athletes.

Variables	Hypo-ferritinemia (n = 22)	Normo-ferritinemia (n = 25)	Odds ratio of univariate analysis	p value	Multivariate Model 1		Multivariate Model 2
					Adjusted odds ratio	p value	Adjusted odds ratio	p value
Age (years)	19 [19,20]	20 [19–21]	0.77 [0.44 − 1.35]	0.36	0.68 [0.28 − 1.63]	0.38	0.82 [0.34 − 2.01]	0.67
Years of sports/athletics	9 [7–13]	13 [11–15]	0.86 [0.74 − 1.00]	0.053	0.60 [0.42 − 0.87]	0.007	0.62 [0.43 − 0.90]	0.01
Affiliated club
Kendo	8 (36)	12 (48)	1 (reference)		1 (reference)		1 (reference)
Handball	10 (45)	10 (40)	1.50 [0.43 − 5.25]	0.44	0.52 [0.05 − 4.95]	0.57	0.77 [0.08 − 7.45]	0.77
Badminton	4 (18)	3 (12)	2.00 [0.35 − 11.44]	0.53	358.4 [2.5 − 5.1×10^4]	0.02	−	−
Body mass index (kg/m^2)	23.2 [21.9–24.8]	23.1 [21.7–24.1]	1.01 [0.79 − 1.28]	0.96	1.66 [1.01 − 2.71]	0.045	1.55 [0.94 − 2.56]	0.08
History of anemia*	4 (18)	1 (4)	0.31 [0.42 − 15.55]	0.31	−	−	−	−
Previous use of oral iron supplement*	13 (59)	7 (29)	3.71 [1.10 − 12.56]	0.03	−	−	−	−
FFQg survey^†
Dietary energy intake (kcal)	1,984 [1],479- [2],200]	1,835 [1],709- [2],376]	1.00 [0.99 − 1.00]	0.86	0.99 [0.99 − 0.999]	0.02	0.994 [0.989 − 0.999]	0.04
Dietary iron intake (mg)^‡	6.6 [5.0–7.7]	5.9 [5.0–8.4]	1.04 [0.76 − 1.41]	0.82	4.90 [1.34 − 17.98]	0.02	4.40 [1.12 − 17.26]	0.03

Median [interquartile range] or number (percentage) are shown. *A female in the normo-ferritinemia group was missed. History of anemia and previous use of oral iron supplement were not included in the multivariate logistic model due to collinearity. ^†Three and two females were missed in hypo- and normo-ferritinemia groups. The multivariate model 2 excluded the badminton club due to the potential small-sample bias.

Abbreviations: aOR; adjusted odds ratio, FFQg; food-frequency questionnaire based on food groups, OR; odds ratio. ^‡Fe intake is defined as dietary intake.

Ekenros, L, von Rosen, P, Solli, GS, et al. Perceived impact of the menstrual cycle and hormonal contraceptives on physical exercise and performance in 1,086 athletes from 57 sports. Front Physiol. 2022;13:954760. doi: 10.3389/fphys.2022.954760

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