158
Effects of Iron Supplementation in Female Athletes with Low Serum Ferritin Concentration M. Fogelholm1 , L. Jaakkola2 , T Lampisjärvi3 'Department of Nutrition, University of Helsinki, Helsinki, Finland -Research Institute for Sports Medicine in Helsinki, Finland 3Finnish Recreational Sports Association, Helsinki, Finland
M Fogeihoim, L. Jaakkola and T Lampisjärvi, Effects of Iron Supplementation in Female Athletes with Low Serum Ferritin Concentration. Tnt J Sports Mcd, Vol 13,No2,pp 158—162,1992. Low serum ferritin concentrations are commonly found in female athletes. By studying the effects of an 8-week iron or placebo supplementation in 31 female athletes (aged 17—31 years), with an initial serum ferritin
concentration 25 tg/l and blood hemoglobin 120 g/l,
deficiency (storage iron depletion, but still normal erythropoiesis) on work performance (1, 3). Since female athletes, particularly, may have an increased risk of prelatent iron deficiency (6, 8, 10, 13, 18), this is an important question to examine. Low serum ferritin concentration typically indicates prelatent iron deficiency or storage iron depletion (2). Some investigators have reported an increase in exercise-in-
duced blood lactate concentration (20) or a decrease in endurance performance (19) in female athletes with low serum ferritin values. In contrast, some others have found no relationship between storage iron and exercise-induced blood lactate concentration or VO2max (11, 12, 22).
we investigated whether low serum ferritin values hinder
aerobic performance. Serum ferritin concentration increased from 14 (25th and 75th percentile: 11, 21) to 26 (18, 36) tg/l in the iron-supplemented group, but remained at a
low 11(9, 17) tg/l in the placebo group (group difference
after supplementation: p 0.001). Before supplementation, blood hemoglobin concentration was not different in the two groups. After supplementation, however, the concentration in the iron group was 139 (135, 144) g/l and 128
(126, 134) g/1 in the placebo group (group difference: p = 0.00 1). Iron supplementation did not affect blood lactate concentration or VO2max during an incremental ergometer test. Hence, aerobic performance was not impaired in nonanemic female athletes with serum ferritin 25 .rg/l. Key words
Blood lactate, female athletes, ferritin, iron status, iron supplementation, physical performance
Opinions vary as to the relevance of low serum ferritin concentration on physical performance (11 —14). In the
present study, we examined effects of an 8-wk iron-supplementation program on biochemical indices of iron status and physical performance, indicated by exercise-induced blood lactate concentration, and maximal oxygen consumption (VO2max). All participants were female athletes, with an initial serum ferritin concentration 25 l.tg/l. Subjects and Methods
Thirty-three female athletes, aged 17 to 31 years, were selected for this study. Inclusion criteria concern-
ing iron status were serum ferritin concentration 25 sg/l and blood hemoglobin concentration 120 g/l. All subjects participated regularly in competitive sports.
The subjects were randomized into iron or placebo groups, using random permuted blocks within strata, in a double blind manner (17). Their menarcheal state (regular or irregular) was used as the stratifying factor.
Since two subjects from the iron group Introduction
Iron deficiency anemia leads to decreased exercise tolerance and impaired work performance (3). In anemia, blood hemoglobin concentration declines, impairing the blood's capacity to deliver oxygen to working muscles (15). Less attention has been paid to the effects of prelatent iron mt. J. Sports Med. 13(1992)158—162 GeorgThieme Verlag Stuttgart New York
dropped out of the study because of illness, the final number of subjects was 31 (Table 1). Six of the subjects (three in the iron group and three in the placebo group) competed in long-distance running or orienteering. The rest were involved in team-
sports, such as football, Finnish baseball, basketball and handball. Time spent in training was calculated from a short questionnaire. Percentage of body fat was estimated from the sum of four skinfolds (4).
An informed consent was obtained from all subjects. The study was approved by the ethical committee of
Downloaded by: Universite Laval. Copyrighted material.
Abstract
hit. J. Sports Med. 13 (1992) 159
Iron Supplementation in Female Athletes with Low Serum Ferritin Concentration Table 1
Characteristics of subjects.
Iron group
proximately 1 W/kg), while the highest workload tolerated by Placebo group
n=14
n=17
median (25th, 75th) 1 median (25th, 75th)
Age (years) Height (cm) Weight (kg) Body fat (%) Training (h/mo)
24 63
(21, (155, (60,
21
(18,
32
(28,
171
26)
21
182)
(168 59 23 36
69) 22) 38)
(20, 163, (57,
(20, (29,
24) 174) 65) 25) 44)
125th and 75th percentiles.
the subjects varied between 150 and 275 W. This test took place both at the beginning and end of the study period, precisely at the same time of the day. A light meal was allowed 3 h before the test.
Heart rate was monitored by the Diascope 2 ECG-pulse amplifier (S & Medico Teknik A/S, Alberts!und, Denmark). Expired gases were sampled and analysed by the Oxycon-4 gas analyser (Mijnhardt, The Netherlands). The device was calibrated before and after each test.
At the end of each 3-mm workload, a skin sinki.
Supplementation and assessment of dietary habits Subjects took either one plac®ebo or one iron tablet (100 rng iron as ferrous sulfate, Retafer ; Orion-yhtymä Oy, Espoo, Finland), daily, for 8 weeks. To ensure good iron absorption, all subjects were asked to take their tablets between their main meals, and together with fruit, fruit juice fortified with vitamin C, or with a vitamin C supplement. The sub-
puncture blood sample was taken from the fingertip. Blood lactate concentration was immediately analysed (YSI Model 23L Lactate Analyzer; Yellow Springs Instrument Co, Ltd., Ohio, USA). The principle of this device is based on the catalytic action of L-lactate oxidase and FAD on oxygen and L-lac-
tate. Hydrogen peroxide, produced in the above reaction, is quantitated electrochemically.
Statistical analyses
jects were given written information on how to compose a
Because of skewed lactate and ferritin distributions, all results are given as median values and 25th and 75th percentiles of the respective cumulative distribution.
well-balanced diet. Excluding the protocol tablet and vitamin
BMDP statistical software was used for statistical analyses.
C, no other dietary supplements were allowed during the study.
Mann-Whitney's U-test was used to test differences between the groups, and Wilcoxon's test to examine dif-
To ascertain whether any major dietary differences existed between the two groups, subjects were requested
ferences between values before and after supplementation (BMDP 3D program). p < 0.05 was used as the accepted level
to fill out short questionnaires at the end of the study. Questions about the consumption frequency of milk products,
of significance for the background factors (age, height, weight, percentage of body fat, training) and food consumption. Com-
cereal products, fruits, vegetables, berries, meat, fish, liver, tea, and coffee were asked.
parisons of iron status indicators and maximal oxygen consumption (VO2max) involved 4 tests, namely, difference between groups before and after the treatment, and difference between pre- and post-supplementation values in both groups.
Biochemical analyses and exercise tests Blood samples for iron status analyses were taken both at the beginning and end of the study period. After an overnight fast, the sample was drawn between 8 and 9 a. m. from the antecubital vein, in vacuum tubes (Venoject ). Before the sample draw, subjects rested for 10 minutes.
Blood hemoglobin concentration and hematocrit (packed cell volume) value were determined within two hours from sampling (device: LK 540; LIC Instrument, Solna,
To avoid false significances, the accepted p-value was reduced to 0.01 (17).
For comparisons of blood lactate concentration, heart rate, oxygen consumption during the exercise test, the 5 highest workloads tolerated by each subject (referred to as Wl = lowest, W2, W3, W4 and W5 = highest) were examined. Mann-Whitney's U-test and Wilcoxon's test were used as explained above. The accepted level of significance was p
Effects of Iron Supplementation in Female Athletes with Low Serum Ferritin Concentration M. Fogelholm1 , L. Jaakkola2 , T Lampisjärvi3 'Department of Nutrition, University of Helsinki, Helsinki, Finland -Research Institute for Sports Medicine in Helsinki, Finland 3Finnish Recreational Sports Association, Helsinki, Finland
M Fogeihoim, L. Jaakkola and T Lampisjärvi, Effects of Iron Supplementation in Female Athletes with Low Serum Ferritin Concentration. Tnt J Sports Mcd, Vol 13,No2,pp 158—162,1992. Low serum ferritin concentrations are commonly found in female athletes. By studying the effects of an 8-week iron or placebo supplementation in 31 female athletes (aged 17—31 years), with an initial serum ferritin
concentration 25 tg/l and blood hemoglobin 120 g/l,
deficiency (storage iron depletion, but still normal erythropoiesis) on work performance (1, 3). Since female athletes, particularly, may have an increased risk of prelatent iron deficiency (6, 8, 10, 13, 18), this is an important question to examine. Low serum ferritin concentration typically indicates prelatent iron deficiency or storage iron depletion (2). Some investigators have reported an increase in exercise-in-
duced blood lactate concentration (20) or a decrease in endurance performance (19) in female athletes with low serum ferritin values. In contrast, some others have found no relationship between storage iron and exercise-induced blood lactate concentration or VO2max (11, 12, 22).
we investigated whether low serum ferritin values hinder
aerobic performance. Serum ferritin concentration increased from 14 (25th and 75th percentile: 11, 21) to 26 (18, 36) tg/l in the iron-supplemented group, but remained at a
low 11(9, 17) tg/l in the placebo group (group difference
after supplementation: p 0.001). Before supplementation, blood hemoglobin concentration was not different in the two groups. After supplementation, however, the concentration in the iron group was 139 (135, 144) g/l and 128
(126, 134) g/1 in the placebo group (group difference: p = 0.00 1). Iron supplementation did not affect blood lactate concentration or VO2max during an incremental ergometer test. Hence, aerobic performance was not impaired in nonanemic female athletes with serum ferritin 25 .rg/l. Key words
Blood lactate, female athletes, ferritin, iron status, iron supplementation, physical performance
Opinions vary as to the relevance of low serum ferritin concentration on physical performance (11 —14). In the
present study, we examined effects of an 8-wk iron-supplementation program on biochemical indices of iron status and physical performance, indicated by exercise-induced blood lactate concentration, and maximal oxygen consumption (VO2max). All participants were female athletes, with an initial serum ferritin concentration 25 l.tg/l. Subjects and Methods
Thirty-three female athletes, aged 17 to 31 years, were selected for this study. Inclusion criteria concern-
ing iron status were serum ferritin concentration 25 sg/l and blood hemoglobin concentration 120 g/l. All subjects participated regularly in competitive sports.
The subjects were randomized into iron or placebo groups, using random permuted blocks within strata, in a double blind manner (17). Their menarcheal state (regular or irregular) was used as the stratifying factor.
Since two subjects from the iron group Introduction
Iron deficiency anemia leads to decreased exercise tolerance and impaired work performance (3). In anemia, blood hemoglobin concentration declines, impairing the blood's capacity to deliver oxygen to working muscles (15). Less attention has been paid to the effects of prelatent iron mt. J. Sports Med. 13(1992)158—162 GeorgThieme Verlag Stuttgart New York
dropped out of the study because of illness, the final number of subjects was 31 (Table 1). Six of the subjects (three in the iron group and three in the placebo group) competed in long-distance running or orienteering. The rest were involved in team-
sports, such as football, Finnish baseball, basketball and handball. Time spent in training was calculated from a short questionnaire. Percentage of body fat was estimated from the sum of four skinfolds (4).
An informed consent was obtained from all subjects. The study was approved by the ethical committee of
Downloaded by: Universite Laval. Copyrighted material.
Abstract
hit. J. Sports Med. 13 (1992) 159
Iron Supplementation in Female Athletes with Low Serum Ferritin Concentration Table 1
Characteristics of subjects.
Iron group
proximately 1 W/kg), while the highest workload tolerated by Placebo group
n=14
n=17
median (25th, 75th) 1 median (25th, 75th)
Age (years) Height (cm) Weight (kg) Body fat (%) Training (h/mo)
24 63
(21, (155, (60,
21
(18,
32
(28,
171
26)
21
182)
(168 59 23 36
69) 22) 38)
(20, 163, (57,
(20, (29,
24) 174) 65) 25) 44)
125th and 75th percentiles.
the subjects varied between 150 and 275 W. This test took place both at the beginning and end of the study period, precisely at the same time of the day. A light meal was allowed 3 h before the test.
Heart rate was monitored by the Diascope 2 ECG-pulse amplifier (S & Medico Teknik A/S, Alberts!und, Denmark). Expired gases were sampled and analysed by the Oxycon-4 gas analyser (Mijnhardt, The Netherlands). The device was calibrated before and after each test.
At the end of each 3-mm workload, a skin sinki.
Supplementation and assessment of dietary habits Subjects took either one plac®ebo or one iron tablet (100 rng iron as ferrous sulfate, Retafer ; Orion-yhtymä Oy, Espoo, Finland), daily, for 8 weeks. To ensure good iron absorption, all subjects were asked to take their tablets between their main meals, and together with fruit, fruit juice fortified with vitamin C, or with a vitamin C supplement. The sub-
puncture blood sample was taken from the fingertip. Blood lactate concentration was immediately analysed (YSI Model 23L Lactate Analyzer; Yellow Springs Instrument Co, Ltd., Ohio, USA). The principle of this device is based on the catalytic action of L-lactate oxidase and FAD on oxygen and L-lac-
tate. Hydrogen peroxide, produced in the above reaction, is quantitated electrochemically.
Statistical analyses
jects were given written information on how to compose a
Because of skewed lactate and ferritin distributions, all results are given as median values and 25th and 75th percentiles of the respective cumulative distribution.
well-balanced diet. Excluding the protocol tablet and vitamin
BMDP statistical software was used for statistical analyses.
C, no other dietary supplements were allowed during the study.
Mann-Whitney's U-test was used to test differences between the groups, and Wilcoxon's test to examine dif-
To ascertain whether any major dietary differences existed between the two groups, subjects were requested
ferences between values before and after supplementation (BMDP 3D program). p < 0.05 was used as the accepted level
to fill out short questionnaires at the end of the study. Questions about the consumption frequency of milk products,
of significance for the background factors (age, height, weight, percentage of body fat, training) and food consumption. Com-
cereal products, fruits, vegetables, berries, meat, fish, liver, tea, and coffee were asked.
parisons of iron status indicators and maximal oxygen consumption (VO2max) involved 4 tests, namely, difference between groups before and after the treatment, and difference between pre- and post-supplementation values in both groups.
Biochemical analyses and exercise tests Blood samples for iron status analyses were taken both at the beginning and end of the study period. After an overnight fast, the sample was drawn between 8 and 9 a. m. from the antecubital vein, in vacuum tubes (Venoject ). Before the sample draw, subjects rested for 10 minutes.
Blood hemoglobin concentration and hematocrit (packed cell volume) value were determined within two hours from sampling (device: LK 540; LIC Instrument, Solna,
To avoid false significances, the accepted p-value was reduced to 0.01 (17).
For comparisons of blood lactate concentration, heart rate, oxygen consumption during the exercise test, the 5 highest workloads tolerated by each subject (referred to as Wl = lowest, W2, W3, W4 and W5 = highest) were examined. Mann-Whitney's U-test and Wilcoxon's test were used as explained above. The accepted level of significance was p
