462
Iron Supplementation and Running Performance in Female Cross-Country Runners P. D. Powell, A. Tucker Department of Physiology, Colorado State University, Fort Collins, Corlorado 80523
Abstract P. D. Powell andA. Tucker, Iron Supplementation and Running Performance in Female Cross-Country Runners. IntJ Sports Med, Vol 12, No 5, pp 462—467, 1991.
Accepted: December 15, 1990
There are approximately 4 million female runners in the United States. Of this population, 81% range in age between 18 and 44 years (18). The incidence of iron deficiency in menstruating women has been estimated at 25 % (28). Since women athletes are possibly at higher risk for iron deficiency than nonathletes (14, 16, 33), a legitimate concern exists over the iron status of female runners.
The pupose of this study was to determine the effects of two weeks of high dosage iron supplementation on various blood iron indices and metabolic parameters in
The total smount of iron in an adult is approximately 4 to 5 grams. About 75% of iron has an active physio-
non-anemic, iron-depleted competitive female cross-
logical role. Hemoglobin, myoglobin and oxidation-reduc-
country runners. The subjects were highly trained members
tion enzymes participate in this active role. The remaining iron is present in various storage forms (ferritin, hemosiderin) that can be mobilized when necessary. Only 10 to 15% of ingested iron is absorbed and iron absorption is largely regulated by the
of the Colorado State University cross-country team and were completing 40 to 50 miles of training weekly. A pretest, post-test single-blind corssover design was employed. Upon collection of baseline exercise blood and metabolic data, five subjects were randomly assigned to iron supplementation (650 mg ferrous sulfate; 130 mg elemental iron) and five subjects to placebo treatment. At two weeks the treatments were reversed. Exercise blood and metabolic data were collected at two-week intervals. Dietary iron intake was assessed using a three-day dietary survey. Dietary analysis revealed deficiencies in vitamin B-6, iron, magne-
sium, and zinc according to USRDA standards. Baseline blood samples revealed no deficiencies in iron storage or transport proteins. Two weeks of iron supplementation resulted in no significant increases in blood iron indices. Metabolic parameters related to running performance were also unchanged after iron supplementation. High dosage, short-term iron supplementation appears to have no effect on blood or metabolic parameters in iron-depleted but nonanemic female cross-country runners. Key words
Ferritin, transferrin, TIBC, 02 consumption, lactate, dietary analysis, iron deficiency
body's needs. Iron homeostasis is thus largely controlled by absorption rather than excretion. Therefore, dietary intake coupled with iron loss and excretion are the primary factors involved in iron turnover.
Female endurance runners who train seriously are likely to experience a six-component occupational hazard that depletes iron stores. First, runners probably consume less iron than untrained sedentary people. Current dietary practices minimize meat intake in favor of vegetable protein anda high percentage of complex carbohydrates. Second, iron loss
can occur through sweating (17, 29) during training under warm weather conditions. A third source of loss is via myoglobin iron, which can be lost through renal filtration andexcretion if exertional rhabdomyolysis occurs (34). Fourth, hema-
tuna, a combination of hemolysis (22, 31) and shunting-induced renal vasoconstriction with increased glomerular pressure and increased glomerular permeability (1), can occur. Fifth, runners engaged in race-pace intensity training show a measurably increased loss of blood via the gastrointestinal tract (21, 37). The sixth and last component is that of menstrual blood loss.
Iron deficiency exists in varying degrees, from mild depletion of iron stores to severe anemia. Three stages of increasing deficiency are identified as: Stage 1 — iron depletion, a decrease in storage iron identified by lowered serum ferritin levels (15—35 ng/ml); Stage 2 — iron deficiency without anemia, iron stores are very low, percent transferrin saturation
mt. J. Sports Med. 12(1991)462—467 Georg Thieme Verlag Stuttgart -New York
decreases, and total iron binding capacity increases (serum ferritin, 12—15 ng/ml; hemoglobin > 13 g%); and Stage 3 — iron deficiency with anemia, hemoglobin levels are decreased in addition to above findings (serum ferritin < 12 ng/ml; hemoglobin < 13 g%) (20). Iron deficiency anemia and iron
Downloaded by: Queen's University. Copyrighted material.
Introduction
mt. J. Sports Med. 12(1991) 463
deficiency without anemia are common among female en-
hypothesized that exercise-recovery blood lactate levels
durance runners (3,4, 10, 12, 14, 18, 23, 30, 33). Recent studies also report low iron levels for male endurance athletes as well (4, 9, 16). Evidence also exists to indicate that endurance training reduces body iron stores (9, 19, 38).
would remain unchanged after iron supplementation.
Oral iron therapy (soluble ferrous salts) is used to increase serum ferritin levels, increase transferrin saturation and restore normal hemoglobin values. Cooter and Mowbray (5) and Haymes et al. (13) concluded that a supplementation of 18 mg of iron per day (USRDA) had no effect on the iron status of athletes. Pate et al. (28), using 50mg of elemental iron, reported no changes in the iron status of women athletes over the course of their athletic season. Conversely, in a supplementation study involving high school and college female crosscountry runners, 23 of the 42 subjects (55%) exhibited some degree of iron deficiency with or without anemia. Upon iron
Materials and Methods
Ten trained healthy members of the Colorado State University women's cross-country track team served as subjects. Participants in the study trained all year round, com-
pleting 40 to 50 training miles weekly during competition. They had been running competitively for several years (3.5 to 10 yrs) prior to the investigation, with their distance never falling below twenty-five miles per week, and resided in Fort Collins, CO (5000 ft altitude; PB = 640 mmHg). Prior to initiation
of this investigation, approval was obtained from the Colorado State Univesity Human Research Committee. Each subject provided informed consent for treadmill exercise testing, iron supplementation ingestion and venous blood sam-
supplementation, improvements in serum iron, transferrin and hemoglobin were noted (30). Other studies reported im-
pling, and were allowed to withdraw from the study at any time. Experimental procedures were in accordance with the
proved hemoglobin and serum ferritin concentrations in menstruating women with daily iron supplementation of 105 mg of
policy statement of the American College of Sports Medicine.
ferrous iron (15), increased serum ferritin in iron-deficient
A pre-test, post-test single-blind crossover design was employed. At the outset of the study, baseline data were collected by drawing venous blood samples at the termination of exercise and collecting exercise performance data from each subject. Five subjects were then randomly assigned
cross-country runners ingesting 195 mg iron per day (33), and variable improvements in iron status in iron-deficient female intercollegiate athletes receiving 65 mg iron per day for approximately 3 months (32).
Decreased work performance has been demonstrated in exercising iron-deficient animals, even after their anemia had been corrected by exchange transfusion (11).
However, when iron deficiency was artificially induced in male volunteers, endurance performance was not affected (2).
A rapid benefit of iron treatment has been demonstrated in iron-deficient human subjects with severe and moderate anemia (25), with improved work capacity and lower heart rates (at a given workload) noted after just four days of iron treatment (26). The effect of two weeks of iron therapy on exer-
to iron supplementation (650 mg ferrous sulfate; 130 mg elemental iron) and five subjects were assigned to placebo (lactose-charcoal) treatment. The iron supplement and placebo were packaged in identically sized clear capsules. Each capsule contained a lactose-charcoal mixture. The darkcolored charcoal concealed the presence of the iron in the iron supplementation capsules. All participants were instructed to consume one capsule after the evening meal or at bedtime to avoid undesirable side effects of iron ingestion. Each subject consumed capsules daily for a period of two weeks at which time post-exercise venous blood samples were drawn and performance data collected in a manner similar to the collection of the baseline data. At that point the groups switched treat-
cise performance and exercise-induced lactate production in trained women athletes has recently been studied (35). One group of athletes with normal iron status was compared with another group that had low ferritin, low percent transferrin saturation and minimally decreased hemoglobin values (Stage 2 iron deficiency). Exercise performance was not changed after iron therapy in either group, however, blood lactate levels at maximum exercise in the treated iron-deficient group were significantly lower compared to pre-therapy levels (35).
ments and consumed the new capsules for a period of two weeks. At the end of the second two-week period, post-exercise venous blood samples were drawn and performance data collected as before. A two-week ingestion period has been shown to increase blood iron indices (35). However, there is little evidence to indicate any residual effect of iron sup-
The focus of previous studies has been to determine metabolic responses to iron supplementation in anemic
Ventilation was measured by attaching a Ventilation Measurement Module (Alpha Technologies mc, VMM
(Stage 3 iron deficiency) and borderline anemic subjects
110 series) to the inspiratory side of a Hans-Rudolph valve. Expired gases were passed to a plexiglas mixing chamber where gas samples were continuously drawn through drierite columns to an 02 analyzer (Applied Technical Products, Oxygen Analyzer 101) and a CO2 analyzer (Ametek P61B). The analog outputs from the VMM, 02 and CO2 analyzers were
(Stage 2 iron deficiency). There is a need to determine metabolic responses to iron supplementation in iron-depleted athletes with otherwise normal iron indices (Stage I iron deficiency). Therefore, the purpose of the present study was to determine the effect of iron supplementation on both blood iron indices and metabolic parameters in female cross-country runners with low iron stores (Stage I iron deficiency). We hypothesized that iron supplementation would not alter normal blood iron indices or submaximal oxygen consumption in this group of runners, since adequate iron was still available for non-hematological, iron-related metabolic functions. We also
plementation following crossover to placebo.
Treadmill Testing
converted to digital signals with an AID converter (Lab Master) and fed into an NCR personal computer. C02 production, 02 consumption, respiratory exchange ratio (RER), and ventilation were calculated using a software program designed for determining metabolic parameters (6).
Downloaded by: Queen's University. Copyrighted material.
Iron Supplementation and Running Performance
464 mt. J. Sports Med. 12(1991)
P. D. Powell, A. Tucker
Table 1 Blood data for runners during baseline, iron supplementation and placebo treatments Normal ranges HCT (%)
HB (g%) RBC (x106/ml)
38—45 12—16 4.0—5.0
WBC
82—98 30—36 6—9 4.5—11.0
(x103/til) Platelets
200—400
MCV (i.i) MCI-IC (%)
Protein (%)
Baseline (n = 10)
12—135
27—139 250—420
Placebo (n = 10)
43.2
2.1
42.4
1.2
43.0
14.7
0.7 0.19
14.6
0.4 0.16
14.7
4.72
4.63
4.70
1.6 0.6 0.19
92
2.7
92
3.2
8.6 9.4
3.6 0.4 0.5 2.7
35 8.6 9.2
0.5 0.3
0.4 0.5
1.8
34 8.6 8.3
367
65
370
49
337
57
91
34
(x103/il) Ferritin (ng/ml) Haptoglobin (mgfdl) TIBC
Iron (n = 10)
29.1
60
14.1 a
51.6
249b
44.1
1.5
21.8
26.1 a
241
139a
270
45.9
255
185b
71
377a
60
25.7
67
33•7b
29.1
14.7a
22.4
9.3
25.9
Fe
55—185
(l.tg/dl) Transferrin (%)
20—55
12.7
a_8. bfl9: — Denotes that tests were not performed;
All values are means±Sd.
Five minutes of resting (seated) metabolic data were collected and then a 20-minute endurance running proto-
col (simulating race pace) was utilized for the exercise test.
Treadmill grade and running speed were adjusted to individual ability (range: 0 to 2 ° for grade, 7.6 to 10 mph for speed). Metabolic parameters were measured during the last five minutes of the treadmill exercise. Upon completion of the exercise, a one-minute post-exercise venous blood sample was obtained from the seated subject.
Blood Sampling Venous blood was drawn from the antecubital vein immediately after the completion of the exercise bout. Blood parameters that were analyzed included serum iron, total iron binding capacity, serum ferritin, serum haptoglobin, hematocrit, hemoglobin, mean corpuscular hemoglobin concentration, mean corpuscular volume, plasma protein concentration, platelet and white cell counts, and lactate (Sigma lactate kit).
Dietary Analysis Dietary iron intake was assessed using a threeday dietary survey. One day of each survey was either a Satur-
day or Sunday as individual eating habits tend to vary on weekends. Data analysis was completed using the Nutrifit (24) computer program.
Statistical Analysis The baseline blood and metabolic data were compared using independent t-tests (Minitab computer program) to insure that no significant differences existed between
the experimental groups at the outset of the study. To determine if significant changes had occurred within the same group throughout the 4-week experimental period, dependent t-tests were used. A significance level of p
Iron Supplementation and Running Performance in Female Cross-Country Runners P. D. Powell, A. Tucker Department of Physiology, Colorado State University, Fort Collins, Corlorado 80523
Abstract P. D. Powell andA. Tucker, Iron Supplementation and Running Performance in Female Cross-Country Runners. IntJ Sports Med, Vol 12, No 5, pp 462—467, 1991.
Accepted: December 15, 1990
There are approximately 4 million female runners in the United States. Of this population, 81% range in age between 18 and 44 years (18). The incidence of iron deficiency in menstruating women has been estimated at 25 % (28). Since women athletes are possibly at higher risk for iron deficiency than nonathletes (14, 16, 33), a legitimate concern exists over the iron status of female runners.
The pupose of this study was to determine the effects of two weeks of high dosage iron supplementation on various blood iron indices and metabolic parameters in
The total smount of iron in an adult is approximately 4 to 5 grams. About 75% of iron has an active physio-
non-anemic, iron-depleted competitive female cross-
logical role. Hemoglobin, myoglobin and oxidation-reduc-
country runners. The subjects were highly trained members
tion enzymes participate in this active role. The remaining iron is present in various storage forms (ferritin, hemosiderin) that can be mobilized when necessary. Only 10 to 15% of ingested iron is absorbed and iron absorption is largely regulated by the
of the Colorado State University cross-country team and were completing 40 to 50 miles of training weekly. A pretest, post-test single-blind corssover design was employed. Upon collection of baseline exercise blood and metabolic data, five subjects were randomly assigned to iron supplementation (650 mg ferrous sulfate; 130 mg elemental iron) and five subjects to placebo treatment. At two weeks the treatments were reversed. Exercise blood and metabolic data were collected at two-week intervals. Dietary iron intake was assessed using a three-day dietary survey. Dietary analysis revealed deficiencies in vitamin B-6, iron, magne-
sium, and zinc according to USRDA standards. Baseline blood samples revealed no deficiencies in iron storage or transport proteins. Two weeks of iron supplementation resulted in no significant increases in blood iron indices. Metabolic parameters related to running performance were also unchanged after iron supplementation. High dosage, short-term iron supplementation appears to have no effect on blood or metabolic parameters in iron-depleted but nonanemic female cross-country runners. Key words
Ferritin, transferrin, TIBC, 02 consumption, lactate, dietary analysis, iron deficiency
body's needs. Iron homeostasis is thus largely controlled by absorption rather than excretion. Therefore, dietary intake coupled with iron loss and excretion are the primary factors involved in iron turnover.
Female endurance runners who train seriously are likely to experience a six-component occupational hazard that depletes iron stores. First, runners probably consume less iron than untrained sedentary people. Current dietary practices minimize meat intake in favor of vegetable protein anda high percentage of complex carbohydrates. Second, iron loss
can occur through sweating (17, 29) during training under warm weather conditions. A third source of loss is via myoglobin iron, which can be lost through renal filtration andexcretion if exertional rhabdomyolysis occurs (34). Fourth, hema-
tuna, a combination of hemolysis (22, 31) and shunting-induced renal vasoconstriction with increased glomerular pressure and increased glomerular permeability (1), can occur. Fifth, runners engaged in race-pace intensity training show a measurably increased loss of blood via the gastrointestinal tract (21, 37). The sixth and last component is that of menstrual blood loss.
Iron deficiency exists in varying degrees, from mild depletion of iron stores to severe anemia. Three stages of increasing deficiency are identified as: Stage 1 — iron depletion, a decrease in storage iron identified by lowered serum ferritin levels (15—35 ng/ml); Stage 2 — iron deficiency without anemia, iron stores are very low, percent transferrin saturation
mt. J. Sports Med. 12(1991)462—467 Georg Thieme Verlag Stuttgart -New York
decreases, and total iron binding capacity increases (serum ferritin, 12—15 ng/ml; hemoglobin > 13 g%); and Stage 3 — iron deficiency with anemia, hemoglobin levels are decreased in addition to above findings (serum ferritin < 12 ng/ml; hemoglobin < 13 g%) (20). Iron deficiency anemia and iron
Downloaded by: Queen's University. Copyrighted material.
Introduction
mt. J. Sports Med. 12(1991) 463
deficiency without anemia are common among female en-
hypothesized that exercise-recovery blood lactate levels
durance runners (3,4, 10, 12, 14, 18, 23, 30, 33). Recent studies also report low iron levels for male endurance athletes as well (4, 9, 16). Evidence also exists to indicate that endurance training reduces body iron stores (9, 19, 38).
would remain unchanged after iron supplementation.
Oral iron therapy (soluble ferrous salts) is used to increase serum ferritin levels, increase transferrin saturation and restore normal hemoglobin values. Cooter and Mowbray (5) and Haymes et al. (13) concluded that a supplementation of 18 mg of iron per day (USRDA) had no effect on the iron status of athletes. Pate et al. (28), using 50mg of elemental iron, reported no changes in the iron status of women athletes over the course of their athletic season. Conversely, in a supplementation study involving high school and college female crosscountry runners, 23 of the 42 subjects (55%) exhibited some degree of iron deficiency with or without anemia. Upon iron
Materials and Methods
Ten trained healthy members of the Colorado State University women's cross-country track team served as subjects. Participants in the study trained all year round, com-
pleting 40 to 50 training miles weekly during competition. They had been running competitively for several years (3.5 to 10 yrs) prior to the investigation, with their distance never falling below twenty-five miles per week, and resided in Fort Collins, CO (5000 ft altitude; PB = 640 mmHg). Prior to initiation
of this investigation, approval was obtained from the Colorado State Univesity Human Research Committee. Each subject provided informed consent for treadmill exercise testing, iron supplementation ingestion and venous blood sam-
supplementation, improvements in serum iron, transferrin and hemoglobin were noted (30). Other studies reported im-
pling, and were allowed to withdraw from the study at any time. Experimental procedures were in accordance with the
proved hemoglobin and serum ferritin concentrations in menstruating women with daily iron supplementation of 105 mg of
policy statement of the American College of Sports Medicine.
ferrous iron (15), increased serum ferritin in iron-deficient
A pre-test, post-test single-blind crossover design was employed. At the outset of the study, baseline data were collected by drawing venous blood samples at the termination of exercise and collecting exercise performance data from each subject. Five subjects were then randomly assigned
cross-country runners ingesting 195 mg iron per day (33), and variable improvements in iron status in iron-deficient female intercollegiate athletes receiving 65 mg iron per day for approximately 3 months (32).
Decreased work performance has been demonstrated in exercising iron-deficient animals, even after their anemia had been corrected by exchange transfusion (11).
However, when iron deficiency was artificially induced in male volunteers, endurance performance was not affected (2).
A rapid benefit of iron treatment has been demonstrated in iron-deficient human subjects with severe and moderate anemia (25), with improved work capacity and lower heart rates (at a given workload) noted after just four days of iron treatment (26). The effect of two weeks of iron therapy on exer-
to iron supplementation (650 mg ferrous sulfate; 130 mg elemental iron) and five subjects were assigned to placebo (lactose-charcoal) treatment. The iron supplement and placebo were packaged in identically sized clear capsules. Each capsule contained a lactose-charcoal mixture. The darkcolored charcoal concealed the presence of the iron in the iron supplementation capsules. All participants were instructed to consume one capsule after the evening meal or at bedtime to avoid undesirable side effects of iron ingestion. Each subject consumed capsules daily for a period of two weeks at which time post-exercise venous blood samples were drawn and performance data collected in a manner similar to the collection of the baseline data. At that point the groups switched treat-
cise performance and exercise-induced lactate production in trained women athletes has recently been studied (35). One group of athletes with normal iron status was compared with another group that had low ferritin, low percent transferrin saturation and minimally decreased hemoglobin values (Stage 2 iron deficiency). Exercise performance was not changed after iron therapy in either group, however, blood lactate levels at maximum exercise in the treated iron-deficient group were significantly lower compared to pre-therapy levels (35).
ments and consumed the new capsules for a period of two weeks. At the end of the second two-week period, post-exercise venous blood samples were drawn and performance data collected as before. A two-week ingestion period has been shown to increase blood iron indices (35). However, there is little evidence to indicate any residual effect of iron sup-
The focus of previous studies has been to determine metabolic responses to iron supplementation in anemic
Ventilation was measured by attaching a Ventilation Measurement Module (Alpha Technologies mc, VMM
(Stage 3 iron deficiency) and borderline anemic subjects
110 series) to the inspiratory side of a Hans-Rudolph valve. Expired gases were passed to a plexiglas mixing chamber where gas samples were continuously drawn through drierite columns to an 02 analyzer (Applied Technical Products, Oxygen Analyzer 101) and a CO2 analyzer (Ametek P61B). The analog outputs from the VMM, 02 and CO2 analyzers were
(Stage 2 iron deficiency). There is a need to determine metabolic responses to iron supplementation in iron-depleted athletes with otherwise normal iron indices (Stage I iron deficiency). Therefore, the purpose of the present study was to determine the effect of iron supplementation on both blood iron indices and metabolic parameters in female cross-country runners with low iron stores (Stage I iron deficiency). We hypothesized that iron supplementation would not alter normal blood iron indices or submaximal oxygen consumption in this group of runners, since adequate iron was still available for non-hematological, iron-related metabolic functions. We also
plementation following crossover to placebo.
Treadmill Testing
converted to digital signals with an AID converter (Lab Master) and fed into an NCR personal computer. C02 production, 02 consumption, respiratory exchange ratio (RER), and ventilation were calculated using a software program designed for determining metabolic parameters (6).
Downloaded by: Queen's University. Copyrighted material.
Iron Supplementation and Running Performance
464 mt. J. Sports Med. 12(1991)
P. D. Powell, A. Tucker
Table 1 Blood data for runners during baseline, iron supplementation and placebo treatments Normal ranges HCT (%)
HB (g%) RBC (x106/ml)
38—45 12—16 4.0—5.0
WBC
82—98 30—36 6—9 4.5—11.0
(x103/til) Platelets
200—400
MCV (i.i) MCI-IC (%)
Protein (%)
Baseline (n = 10)
12—135
27—139 250—420
Placebo (n = 10)
43.2
2.1
42.4
1.2
43.0
14.7
0.7 0.19
14.6
0.4 0.16
14.7
4.72
4.63
4.70
1.6 0.6 0.19
92
2.7
92
3.2
8.6 9.4
3.6 0.4 0.5 2.7
35 8.6 9.2
0.5 0.3
0.4 0.5
1.8
34 8.6 8.3
367
65
370
49
337
57
91
34
(x103/il) Ferritin (ng/ml) Haptoglobin (mgfdl) TIBC
Iron (n = 10)
29.1
60
14.1 a
51.6
249b
44.1
1.5
21.8
26.1 a
241
139a
270
45.9
255
185b
71
377a
60
25.7
67
33•7b
29.1
14.7a
22.4
9.3
25.9
Fe
55—185
(l.tg/dl) Transferrin (%)
20—55
12.7
a_8. bfl9: — Denotes that tests were not performed;
All values are means±Sd.
Five minutes of resting (seated) metabolic data were collected and then a 20-minute endurance running proto-
col (simulating race pace) was utilized for the exercise test.
Treadmill grade and running speed were adjusted to individual ability (range: 0 to 2 ° for grade, 7.6 to 10 mph for speed). Metabolic parameters were measured during the last five minutes of the treadmill exercise. Upon completion of the exercise, a one-minute post-exercise venous blood sample was obtained from the seated subject.
Blood Sampling Venous blood was drawn from the antecubital vein immediately after the completion of the exercise bout. Blood parameters that were analyzed included serum iron, total iron binding capacity, serum ferritin, serum haptoglobin, hematocrit, hemoglobin, mean corpuscular hemoglobin concentration, mean corpuscular volume, plasma protein concentration, platelet and white cell counts, and lactate (Sigma lactate kit).
Dietary Analysis Dietary iron intake was assessed using a threeday dietary survey. One day of each survey was either a Satur-
day or Sunday as individual eating habits tend to vary on weekends. Data analysis was completed using the Nutrifit (24) computer program.
Statistical Analysis The baseline blood and metabolic data were compared using independent t-tests (Minitab computer program) to insure that no significant differences existed between
the experimental groups at the outset of the study. To determine if significant changes had occurred within the same group throughout the 4-week experimental period, dependent t-tests were used. A significance level of p
