The effects of fitness-type exercise on iron status in adult women

Timing of ergogenic aids and micronutrients on muscle and exercise performance

The timing of macronutrient ingestion in relation to exercise is a purported strategy to augment muscle accretion, muscle and athletic performance, and recovery. To date, the majority of macronutrient nutrient timing research has focused on carbohydrate and protein intake. However, emerging research suggests that the strategic ingestion of various ergogenic aids and micronutrients may also have beneficial effects. Therefore, the purpose of this narrative review is to critically evaluate and summarize the available literature examining the timing of ergogenic aids (caffeine, creatine, nitrates, sodium bicarbonate, beta-alanine) and micronutrients (iron, calcium) on muscle adaptations and exercise performance. In summary, preliminary data is available to indicate the timing of caffeine, nitrates, and creatine monohydrate may impact outcomes such as exercise performance, strength gains and other exercise training adaptations. Furthermore, data is available to suggest that timing the administration of beta-alanine and sodium bicarbonate may help to minimize known untoward adverse events while maintaining potential ergogenic outcomes. Finally, limited data indicates that timed ingestion of calcium and iron may help with the uptake and metabolism of these nutrients. While encouraging, much more research is needed to better understand how timed administration of these nutrients and others may impact performance, health, or other exercise training outcomes.

Effects of Exercise on the Resting Heart Rate: A Systematic Review and Meta-Analysis of Interventional Studies

Resting heart rate (RHR) is positively related with mortality. Regular exercise causes a reduction in RHR. The aim of the systematic review was to assess whether regular exercise or sports have an impact on the RHR in healthy subjects by taking different types of sports into account. A systematic literature research was conducted in six databases for the identification of controlled trials dealing with the effects of exercise or sports on the RHR in healthy subjects was performed. The studies were summarized by meta-analyses. The literature search analyzed 191 studies presenting 215 samples fitting the eligibility criteria. 121 trials examined the effects of endurance training, 43 strength training, 15 combined endurance and strength training, 5 additional school sport programs. 21 yoga, 5 tai chi, 3 qigong, and 2 unspecified types of sports. All types of sports decreased the RHR. However, only endurance training and yoga significantly decreased the RHR in both sexes. The exercise-induced decreases of RHR were positively related with the pre-interventional RHR and negatively with the average age of the participants. From this, we can conclude that exercise-especially endurance training and yoga-decreases RHR. This effect may contribute to a reduction in all-cause mortality due to regular exercise or sports.

Randomized, double-blind, placebo-controlled trial of iron supplementation in female soldiers during military training: effects on iron status, physical performance, and mood

BACKGROUND

Decrements in iron status have been reported in female soldiers during military training. Diminished iron status adversely affects physical and cognitive performance.

OBJECTIVE

We wanted to determine whether iron supplementation could prevent decrements in iron status and improve measures of physical performance and cognitive status in female soldiers during basic combat training (BCT).

DESIGN

In this 8-wk randomized, double-blind, placebo-controlled trial, soldier volunteers (n = 219) were provided with capsules containing either 100 mg ferrous sulfate or a placebo. Iron status indicator assays were performed pre- and post-BCT. Two-mile running time was assessed post-BCT; mood was assessed by using the Profile of Mood States questionnaire pre- and post-BCT.

RESULTS

The BCT course affected iron status: red blood cell distribution width and soluble transferrin receptor were elevated (P < 0.05), and serum ferritin was lowered (P < 0.05) post-BCT. Iron supplementation attenuated the decrement in iron status; group-by-time interactions (P < 0.01) were observed for serum ferritin and soluble transferrin receptor. Iron supplementation resulted in improved (P < 0.05) vigor scores on the Profile of Mood States post-BCT and in faster running time (P < 0.05) in volunteers reporting to BCT with iron deficiency anemia.

CONCLUSIONS

Iron status is affected by BCT, and iron supplementation attenuates the decrement in indicators of iron status in female soldiers. Furthermore, iron supplementation may prove to be beneficial for mood and physical performance during the training period. Future efforts should identify and treat female soldiers or athletes who begin training regimens with iron deficiency or iron deficiency anemia.

Iron supplementation maintains ventilatory threshold and improves energetic efficiency in iron-deficient nonanemic athletes

OBJECTIVE

To determine the effect of iron supplementation on iron status and endurance capacity.

DESIGN

Randomized, double-blind iron supplementation.

SETTING

University of Missouri-Columbia and surrounding community.

SUBJECTS

Twenty iron-deficient (serum ferritin, sFer<16 microg/l; serum transferrin receptor, sTfR>8.0 mg/l; or sTfR/log sFer index >4.5), nonanemic (hemoglobin, Hb>120 g/l, women; >130 g/l, men) men and women (18-41 years) were recruited via fliers and newspaper advertisements; 20 of 31 eligible subjects participated.

INTERVENTIONS

A 30 mg measure of elemental iron as ferrous sulfate or placebo daily for 6 weeks.

RESULTS

Dietary iron intake and physical activity did not differ between groups before or after supplementation. Iron supplementation significantly increased sFer compared to placebo (P=0.01), but did not affect Hb or hematocrit. Iron supplementation prevented the decline in ventilatory threshold (VT) observed in the placebo group from pre- to post-supplementation (P=0.01); this effect was greater in individuals with lower sFer before intervention (P<0.05). Changes in sFer from pre- to post-treatment were positively correlated with changes in VT (P=0.03), independent of supplementation. The iron group significantly increased gross energetic efficiency during the submaximal test (P=0.04). Changes in sFer were negatively correlated with changes in average respiratory exchange ratio during the submaximal test (P<0.05).

CONCLUSIONS

Iron supplementation significantly improves iron status and endurance capacity in iron-deficient, nonanemic trained male and female subjects.

Prevalence of iron deficiency with and without anemia in recreationally active men and women

The objective of this study was to determine the prevalence of iron deficiency with and without anemia in a convenience sample of trained male and female adults. One hundred twenty-one adults (72 female, 49 male) involved in aerobic training (11.2+/-6.3 hr/wk for >/=6 consecutive months), ages 18 to 41 years old, participated in an iron status screening. The concentrations of hemoglobin (Hb), ferritin, and transferrin receptor were measured in serum to determine the prevalence of iron deficiency with and without anemia. Eight individuals (seven female, one male) had iron deficiency with anemia (serum ferritin <16 microg/L; Hb<120 g/L female, <136 g/L male). Iron deficiency without anemia (serum ferritin </=16 microg/L) was found in 29% of female and 4% of male subjects. Determination of iron deficiency without anemia using the transferrin receptor-ferritin index (serum transferrin receptor:log serum ferritin>/=4.5) found 36% of female and 6% of male subjects to be iron deficient without anemia. Recreational athletes should be screened for iron deficiency without anemia using serum ferritin, serum transferrin receptor, and Hb.

Iron supplementation improves progressive fatigue resistance during dynamic knee extensor exercise in iron-depleted, nonanemic women

BACKGROUND

Tissue iron depletion may negatively affect endurance performance and muscle fatigability.

OBJECTIVE

We investigated tissue-level iron depletion and progressive fatigue of the quadriceps during dynamic knee-extension exercise in young women.

DESIGN

Twenty iron-depleted (serum ferritin < 20 micro g/L), nonanemic (hemoglobin > 110 g/L) women (macro x +/- SEM age: 29.1 +/- 1.2 y) received iron (iron group) or placebo (placebo group) for 6 wk in a randomized, double-blind trial (n = 10 per group). A protocol integrating 2-3-s maximal voluntary static contractions (MVCs) with dynamic knee extensions was used to assess fatigue.

RESULTS

No significant differences between the groups in baseline iron status, MVC at rest, or MVC at the end of the protocol were observed. After treatment, serum iron and transferrin saturation increased significantly in the iron group (P = 0.02 and P = 0.03, respectively). Serum transferrin receptor concentrations increased significantly in the placebo group (P < 0.01) but not in the iron group. After treatment, the rate of decrease in MVC was attenuated in the iron group but not in the placebo group (P = 0.01). In the iron group, MVC at the sixth minute of the fatigue protocol and MVC at the end of the protocol were approximately 15% (P = 0.04) and approximately 27% higher (P < 0.01), respectively, after treatment. These improvements were not related to changes in iron-status indexes or tissue iron stores, although power was low (< 0.50) to detect these relations.

CONCLUSIONS

Iron supplementation was associated with a significant improvement in muscle fatigability. Interpretation regarding the direct role of tissue iron status is limited by the study's low power to detect relations between tissue iron improvement and decreased muscle fatigue.

Iron supplementation improves endurance after training in iron-depleted, nonanemic women

Our objective was to investigate the effects of iron depletion on adaptation to aerobic exercise, assessed by time to complete a 15-km cycle ergometer test. Forty-two iron-depleted (serum ferritin <16 microg/l), nonanemic (Hb >12 g/dl) women (18-33 yr old) received 100 mg of ferrous sulfate (S) or placebo (P) per day for 6 wk in a randomized, double-blind trial. Subjects trained for 30 min/day, 5 days/wk at 75-85% of maximum heart rate for the final 4 wk of the study. There were no group differences in baseline iron status or in 15-km time. Iron supplementation increased serum ferritin and decreased transferrin receptors in the S compared with the P group. The S and P groups decreased 15-km time and respiratory exchange ratio and increased work rate during the 15-km time trial after training. The decrease in 15-km time was greater in the S than in the P group (P = 0.04) and could be partially attributed to increases in serum ferritin and Hb. These results indicate that iron deficiency without anemia impairs favorable adaptation to aerobic exercise.

Nutritional aspects of immunosuppression in athletes

The literature suggests that a heavy schedule of training and competition leads to immunosuppression in athletes, placing them at a greater risk of opportunistic infection. There are many factors which influence exercise-induced immunosuppression, and nutrition undoubtedly plays a critical role. Misinterpretation of published data and misleading media reports have lead many athletes to adopt an unbalanced dietary regimen in the belief that it holds the key to improved performance. Some sports have strict weight categories, whilst in others low body fat levels are considered to be necessary for optimal performance or seen as an aesthetic advantage. This leads some athletes to consume a diet extremely low in carbohydrate content which, whilst causing rapid weight loss, may have undesirable results which include placing the athlete at risk from several nutrient deficiencies. Complete avoidance of foods high in animal fat reduces the intake of protein and several fat-soluble vitamins. On the other hand, diets with a very high carbohydrate content are usually achieved at the expense of protein. In addition, anecdotal and media reports have often promoted the supposed performance benefits of certain vitamins and minerals, yet most athletes do not realise that micronutrient supplementation is only beneficial when correcting a deficiency, and to date there is little scientific evidence to substantiate claims that micronutrients act as an ergogenic aid. Moreover, excessive intakes of micronutrients can be toxic. Deficiencies or excesses of various dietary components can have a substantial impact on immune function and may further exacerbate the immunosuppression associated with heavy training loads. This review examines the role of nutrition in exercise-induced immunosuppression and the effect of both excessive and insufficient nutrient intake on immunocompetence. As much of the present literature concerning nutrition and immune function is based on studies with sedentary participants, the need for future research which directly investigates the relationship between exercise, training, immunity and nutrition is highlighted.

Twelve weeks of endurance exercise training does not affect iron status measures in women

OBJECTIVE

This study examined the effects of 12 weeks of endurance exercise training on iron status measures in previously inactive women and compared the effects of weight-bearing endurance exercise training and non-weight-bearing endurance exercise on iron status measures.

DESIGN

Randomized, experimental study.

SUBJECTS

Thirty-one healthy, inactive women (aged 23 to 43 years) with apparently normal iron stores (serum ferritin concentration > or = 20 micrograms/L) were recruited from the local area by newspaper advertisements and campus mailings. Twenty-one subjects completed the study (mean +/- standard deviation for age = 32 +/- 5 years, for body mass index = 23.1 +/- 4.9, and for maximum oxygen consumption [VO2max] = 33.8 +/- 6.3 mL/kg per minute).

INTERVENTION

Subjects were randomly assigned to one of three groups: an inactive control group, a walking/running group, or a cycling group. Subjects in the two exercise groups trained three to four times per week at 80% VO2max for 12 weeks. Exercise training sessions were monitored and energy expenditure increased from 150 kcal per session (week 1) to 375 kcal per session (weeks 9 to 12). Subjects in the inactive control group were instructed to maintain their normal activity patterns for the duration of the study. All subjects were instructed to maintain their normal dietary habits.

MAIN OUTCOME MEASURES

Serum ferritin concentration, serum iron concentration, percentage saturation of transferrin, total iron-binding capacity, serum haptoglobin concentration, and other selected hematologic variables were measured at baseline and at weeks 2, 4, 8, and 12.

STATISTICAL ANALYSES

Repeated measures analysis of variance was used to examine group x time interactions in changes in iron status measures. Statistical significance was reached at P < .05.

RESULTS

Analysis of variance indicated that serum ferritin concentration did not change significantly (P = .59) during the 12 weeks in the walking/running group (mean +/- standard deviation from 41.28 +/- 14.22 to 27.41 +/- 9.74 micrograms/L) or the cycling group (from 65.81 +/- 37.62 to 41.06 +/- 26.38 micrograms/L) compared with the control group (from 47.55 +/- 15.87 to 31.56 +/- 10.57 micrograms/L). Values for serum iron, total iron-binding capacity, percentage saturation of transferrin, and haptoglobin also did not change significantly (P > .30) in the walking/running or cycling groups compared with the control group.

APPLICATIONS/CONCLUSIONS

Results of this study suggest that participation in 12 weeks of moderate-intensity endurance exercise training (walking/running or cycling) is not associated with negative effects on selected measures of iron status in healthy, previously untrained women with normal iron stores (serum ferritin > or = 20 micrograms/L).

Micronutrients and exercise: anti-oxidants and minerals

Exercise has been shown to increase indirect measures of lipid peroxidation. However, exercise and training appear to augment the body's anti-oxidant defence system. Whether this augmented defence system can keep up with the increase in lipid peroxidation with exercise is not known. Iron depletion is experienced by many athletes, especially female endurance athletes and adolescents, but iron deficiency anaemia is rare. Iron depletion could affect the ability to train and recover from strenuous exercise, but this has not been examined. There is a concern that female athletes, especially adolescents, are not ingesting sufficient calcium, and this may affect the development of peak bone mass and increase the risk of bone fractures. Further research is needed on mineral and trace mineral intake and loss in athletes. It appears that most athletes have adequate status of chromium, zinc, phosphate and magnesium. Athletes who are restricting energy intake to achieve a low body mass (for example, endurance runners), may not have adequate vitamin or mineral status. More data are needed on vitamin/mineral status of athletes from underdeveloped countries. The general recommendation for athletes is that foods rich in anti-oxidants and minerals should be ingested rather than supplements.

Iron status in women aerobic dance instructors

This investigation evaluated the iron and nutritional status of 12 highly trained aerobic dance instructors who did not take iron supplements (ANS) and 8 who did (AS). A control group (C) consisted of 10 age matched controls. The aerobic instructors had exercised for approximately 3.8 days/wk, 56 min/session for the past 7 yrs. There were no significant differences among groups for energy intake, carbohydrate, protein, fat, nonheme iron, heme iron, or total iron intake (excluding supplemental iron). But both exercise groups had lower ferritin values than the control group. There was also a significant difference in mean cell volume (MCV), with both exercise groups having greater values than the control group. There were no differences among groups for serum iron, total iron binding capacity, transferrin saturation, hematocrit, or hemoglobin. One in three aerobic dance instructors had serum ferritin values below 12 micrograms.L-1. Results indicate that women exercise leaders have iron profiles that are similar to other groups of female athletes. The increased MCV values suggest runners' macrocytosis or an exercise induced macrocytosis.

Exercise performance of collegiate rodeo athletes

In this study we examined the physical, hematologic, and exercise response of 20 male and 10 female athletes of the National Intercollegiate Rodeo Association, Central Rocky Mountain Region. Male subjects were grouped by roughstock, steer wrestling, and roping events. Female athletes were grouped separately. Maximal aerobic capacity, pulmonary ventilation, respiratory exchange ratio, energy expenditure, maximal heart rate, blood pressure, treadmill time, pre- and postexercise lactate, percent body fat, lean body mass, blood chemistry, serum lipids, and reaction/movement time were analyzed by event. No significant differences (P greater than 0.05) were found in any of these categories between male events. Mean resting blood chemistry parameters of rodeo athletes were within normal ranges. Steer wrestling athletes possessed greater body size and lean body mass than other groups. When analyzing body composition, blood pressure, and total cholesterol:high-density lipoprotein (HDL) cholesterol ratios, results indicate average to low risk for coronary heart disease. When compared to other intermittent-activity sport athletes, college rodeo athletes appear to have similar aerobic capacities, but possess lower lean body mass and greater percent body fat.

Iron, transferrin, and haptoglobin levels after a single bout of exercise in men

Twelve, healthy male university student volunteers, between the ages of 20 and 23, were studied. All subjects were considered normal after cardiopulmonary and electrocardiographic examination. The maximal aerobic capacity (Vo2 max) of each subject was determined. The exercise programmes were performed on a mechanically braked Monark cycle ergometer. The subjects were required to perform the three tests, one per week. Each subject had a catheter inserted in an antecubital vein and blood samples were drawn at rest and at the end of exercise. Before and immediately after each exercise session total proteins (TP), hematocrit (Hct), hemoglobin (Hb), and other hematological parameters were measured. Serum iron (Fe), transferrin (TRF), and haptoglobin (HPT) were also determined. Immediately after the end of the exercise (TPT, RST, and IET), TP, Hb, Hct, and RBC increased significantly. TRF and HPT concentrations remained unchanged and iron decreased significantly after maximum sustained test (RST).

Effect of cimetidine on marathon-associated gastrointestinal symptoms and bleeding

Occult gastrointestinal bleeding occurs in 8-30% of marathon runners. We hypothesized that cimetidine would decrease bleeding by reducing acid-mediated injury and conducted a blinded, placebo-controlled prospective trial to determine the impact of cimetidine on gastrointestinal symptoms and bleeding during a marathon. Thirty participants in the 1989 Marine Corps or New York City marathons completed pre- and postrace: (1) a questionnaire evaluating demographic, medication usage, training history, and gastrointestinal symptoms; (2) three consecutive stool Hemoccult (HO) cards; and (3) a stool Hemoquant (HQ). Fourteen runners (CR) took 800 mg of cimetidine by mouth 2 hr before the start and 16 runners (PR) took placebo. Three subjects were HO+ prerace and were not analyzed. Three subjects failed to take drug as directed and were analyzed as PR. Five of 14 PR and two of 13 CR were HO+ postrace (P greater than 0.05). Prerace HQ values (PR: 1.49 +/- 0.6 and CR: 0.60 +/- 0.1 mg hemoglobin/g stool) were not significantly different from postrace HQ values (PR: 0.73 +/- 0.2 and CR: 0.86 +/- 0.2 mg Hgb/g stool). Despite postrace HO+ conversion, no individual postrace HQ became abnormal. The frequency of gastrointestinal symptoms was similar for CR and PR, as well as HO- and HO+ individuals. Cimetidine did not significantly affect occult gastrointestinal bleeding as measured by HO or HQ results. This suggests that marathon-associated gastrointestinal symptoms and bleeding may be due to lesions other than acid-mediated disease or hemorrhagic gastritis.

Exercise as prevention: do the health benefits derive in part from lower iron levels?

The mechanism by which exercise, a key component of modern preventative medicine, protects man from strikingly different diseases such as heart disease and cancer, is largely a mystery. It is proposed that exercise-induced reductions in iron levels, either through iron loss or enhanced iron storage, could be responsible for some of the beneficial effects. Possible roles for iron in coronary artery disease and cancer have recently emerged, particularly as a catalyst for oxygen free radical-induced tissue damage. The iron hypothesis is consistent with the graded reductions in mortality observed as a function of fitness level, and it is the first unified mechanism which can explain the reductions in both heart disease and cancer. If confirmed, preventative medicine in the future will need to include close monitoring of iron levels and, possibly, occasional blood donation for those with moderately high iron stores.

Minerals: exercise performance and supplementation in athletes

This paper examines whether mineral supplements are necessary for athletes, and whether these supplements will enhance performance. Macrominerals (calcium, magnesium, and phosphorus) and trace minerals (zinc, copper, selenium, chromium, and iron) are described. Calcium supplements are important for the health of bones. Athletes tend to have enhanced calcium status as assessed by bone mineral density, with the notable exception of female amenorrhoeic athletes. Magnesium status is adequate for most athletes, and there is no evidence that magnesium supplements can enhance performance. Phosphorus status is adequate for athletes. Phosphorus supplementation over an extended period of time can result in lowered blood calcium, however, some studies have shown that acute 'phosphate loading' will enhance performance. Athletes may have a zinc deficiency induced by poor diet and loss of zinc in sweat and urine. Limited data exist on the relationship of performance and zinc status. Widespread deficiencies in copper have not been documented, and there are no data to suggest that copper supplementation will enhance performance. There is no reason to suspect a selenium deficiency in athletes. The relationship between selenium status and performance has not been established, but selenium may play a role as an antioxidant. Because of the low intakes of chromium for the general population, there is a possibility that athletes may be deficient. Exercise may create a loss in chromium because of increased excretion into the urine. Many athletes, particularly female, are iron depleted, but true iron deficiencies are rare. Iron depletion does not affect exercise performance but iron deficiency anaemia does. Iron supplements have not been shown to enhance performance except where iron deficiency anaemia exists. In conclusion, poor diets are perhaps the main reason for any mineral deficiencies found in athletes, although in certain cases exercise could contribute to the deficiency. Mineral supplementation may be important to ensure good health, but few studies have definitively documented any beneficial effect of mineral supplementation on performance.

Iron deficiency among active men

Iron deficiency in active men is well documented. To assess the relative importance of dietary iron intake, iron absorption, and iron loss in the pathogenesis of this iron deficiency, we compared a group of iron-deficient athletes to a group with normal iron stores. Iron absorption was assessed by an iron tolerance test. Serum haptoglobin was used as a measure of hemolysis. The presence of hemoglobinuria reflected urinary iron loss. Iron intake was determined by a 3-day dietary record as well as a food frequency questionnaire. Results showed iron absorption to be inversely correlated with iron stores. Iron-deficient athletes had higher absorption, suggesting a normal regulation mechanism. Major hemolysis (serum haptoglobin below 40 mg/dl) was found in 28% of subjects with no relationship to iron stores. No hemoglobinuria was detected after a usual training session. Iron intake was elevated in relation to high caloric intake, but iron intake in the form of meat was lower in iron-deficient athletes, as compared to those with normal or repleted iron stores. It is our opinion that inadequate iron intake is an important determinant of iron deficiency in athletes.