Iron metabolism in athletes - achieving a gold standard

Continuous training in young athletes decreases hepcidin secretion and is positively correlated with serum 25(OH)D and ferritin

Background

Iron deficiency is known to impair muscle function and reduce athletic performance, while vitamin D has been reported to induce iron deficiency. However, the mechanism underlying exercise-induced changes in iron metabolism and the involvement of vitamins in this mechanism are unclear. The present study examined changes in biological iron metabolism induced by continuous training and the effects of vitamin D on these changes.

Methods

Diet, physical characteristics, and blood test data were collected from 23 female high school students in a dance club on the last day of each of a 2-month continuous training period and a 2-week complete rest periods.

Results

Serum hepcidin-25 levels were significantly lower during the training period than the rest period (p = 0.013), as were the red blood cell count, hemoglobin, and hematocrit (all p < 0.001). Serum erythropoietin was significantly higher (p = 0.001) during the training period. Significant positive correlations were observed between 25(OH)D levels and serum iron, serum ferritin, and transferrin saturation during the training period. Multiple regression analysis with serum 25(OH)D level as the dependent variable and serum ferritin and iron levels as independent variables during the training period revealed a significant association with serum ferritin.

Conclusion

Continuous training may promote hemolysis and erythropoiesis, contributing to the suppression of hepcidin expression. The relationship between serum 25(OH)D and iron in vivo may be closely related to metabolic changes induced by the exercise load.

Advancing athletic assessment by integrating conventional methods with cutting-edge biomedical technologies for comprehensive performance, wellness, and longevity insights

In modern athlete assessment, the integration of conventional biochemical and ergophysiologic monitoring with innovative methods like telomere analysis, genotyping/phenotypic profiling, and metabolomics has the potential to offer a comprehensive understanding of athletes' performance and potential longevity. Telomeres provide insights into cellular functioning, aging, and adaptation and elucidate the effects of training on cellular health. Genotype/phenotype analysis explores genetic variations associated with athletic performance, injury predisposition, and recovery needs, enabling personalization of training plans and interventions. Metabolomics especially focusing on low-molecular weight metabolites, reveal metabolic pathways and responses to exercise. Biochemical tests assess key biomarkers related to energy metabolism, inflammation, and recovery. Essential elements depict the micronutrient status of the individual, which is critical for optimal performance. Echocardiography provides detailed monitoring of cardiac structure and function, while burnout testing evaluates psychological stress, fatigue, and readiness for optimal performance. By integrating this scientific testing battery, a multidimensional understanding of athlete health status can be achieved, leading to personalized interventions in training, nutrition, supplementation, injury prevention, and mental wellness support. This scientifically rigorous approach hereby presented holds significant potential for improving athletic performance and longevity through evidence-based, individualized interventions, contributing to advances in the field of sports performance optimization.

Effect of Amino Acid Supplementation on Iron Regulation after Endurance Exercise

The purpose of this study was to determine the effects of pre-exercise amino acid (AA) supplementation on post-exercise iron regulation. Ten healthy males participated under two different sets of conditions in a randomized, double-blind, crossover design with a washout period of at least 21 days. Participants received either an AA supplement or placebo (PLA) for five consecutive days (4 g/dose, 3 doses/day). On the sixth day, participants ran on a treadmill for 60 min at 70% of maximal oxygen consumption (V˙O2max). Venous blood samples were collected before (baseline), immediately after, and 1 and 3 h after exercise. The serum hepcidin levels increased significantly 3 h post-exercise in both trials when compared to the baseline (p < 0.001), but the levels were not different between trials. The plasma interleukin-6 (IL-6) level significantly increased immediately after exercise compared to the baseline (p < 0.001) and was significantly higher in the AA trial than in the PLA trial (p = 0.014). Moreover, the exercise-induced increase in serum glycerol level was significantly higher in the AA trial (21.20 ± 3.98 mg/L) than in the PLA trial (17.28 ± 4.47 mg/L, p = 0.017). No significant differences were observed between the AA and PLA trials for serum iron, ferritin, and total ketone body levels (p > 0.05). In conclusion, five days of AA supplementation augmented exercise-induced increases in IL-6 and glycerol in healthy males. However, it did not affect post-exercise iron status or regulation.

REDD1 deletion and treadmill running increase liver hepcidin and gluconeogenic enzymes in male mice

The iron-regulatory hormone hepcidin is transcriptionally up-regulated by gluconeogenic signals. Recent evidence suggeststhat increases in circulating hepcidin may decrease dietary iron absorption following prolonged exercise, however evidence is limited on whether gluconeogenic signals contribute to post-exercise increases in hepcidin. Mice with genetic knockout of regulated in development and DNA response-1 (REDD1) display greater glycogen depletion following exercise, possibly indicating greater gluconeogenesis. The objective of the present study was to determine liver hepcidin, markers of gluconeogenesis and iron metabolism in REDD1 knockout and wild-type mice following prolonged exercise. Twelve-week-old male REDD1 knockout and wild-type mice were randomised to rest or 60 min treadmill running with 1, 3 or 6 h recovery (n = 5-8/genotype/group). Liver gene expression of hepcidin (Hamp) and gluconeogenic enzymes (Ppargc1a, Creb3l3, Pck1, Pygl) were determined by qRT-PCR. Effects of genotype, exercise and their interaction were assessed by two-way ANOVAs with Tukey's post-hoc tests, and Pearson correlations were used to assess the relationships between Hamp and study outcomes. Liver Hamp increased 1- and 4-fold at 3 and 6 h post-exercise, compared to rest (P-adjusted < 0⋅009 for all), and was 50% greater in REDD1 knockout compared to wild-type mice (P = 0⋅0015). Liver Ppargc1a, Creb3l3 and Pck1 increased with treadmill running (P < 0⋅0001 for all), and liver Ppargc1a, Pck1 and Pygl were greater with REDD1 deletion (P < 0⋅02 for all). Liver Hamp was positively correlated with liver Creb3l3 (R = 0⋅62, P < 0⋅0001) and Pck1 (R = 0⋅44, P = 0⋅0014). In conclusion, REDD1 deletion and prolonged treadmill running increased liver Hamp and gluconeogenic regulators of Hamp, suggesting gluconeogenic signalling of hepcidin with prolonged exercise.

Caffeine and alcohol - Friends or foes of human iron stores?

BACKGROUND & AIMS

There is clear evidence that lifestyle factors affect iron bioavailability. However, information regarding the effect of alcohol and caffeine consumption on iron metabolism is limited. The aim of the current study was to evaluate the effect of caffeine and alcohol consumption on iron metabolism in healthy men, regarding their everyday physical activity level.

METHODS

The study enrolled 83 men (59 physically active and 24 sedentary men) aged 18-32 years. Fasting blood samples were collected. ELISA kits were used to determine levels of ferritin, soluble transferrin receptor, hepcidin, hemojuvelin, and C-reactive protein (hsCRP). Level of physical activity was assessed using the International Physical Activity Questionnaire (IPAQ). Caffeine and alcohol intake was assessed using a food frequency questionnaire. A general linear model was performed to evaluate the relationship between caffeine intake and levels of serum ferritin, ferritin, soluble transferrin receptor, hepcidin, hemojuvelin, and hsCRP.

RESULTS

Physically active men (but not sedentary men) who consumed alcohol in excess presented higher ferritin levels when compared to moderate drinkers and abstainers (R2 = 0.35, p = 0.0001). Heavy drinkers presented the highest hepcidin levels when compared to both abstainers and moderate drinkers (p < 0.0001 for physically active, and p = 0.0267 for sedentary men). However, moderate drinkers showed significantly lower hsCRP levels when compared to heavy drinkers and abstainers drinkers (p < 0.0001 for physically active, and p = 0.0116 for sedentary men). Greater caffeine intake was generally associated with greater serum hepcidin levels, with the strongest effect on moderate drinkers. A significant influence of caffeine intake on hsCRP was shown for physically active men but not for sedentary men - greater caffeine intake was connected with higher hsCRP levels for participants who drank alcohol.

CONCLUSION

Based on the presented results it can be assumed that high caffeine consumption may lead to suppression of iron bioavailability through increased inflammation. Furthermore, physical activity and moderate alcohol consumption seemed to benefit reduction of inflammatory response, at least as represented by hsCRP levels.

Effect of an acute exercise on early responses of iron and iron regulatory proteins in young female basketball players

Background

The accumulation of physiological stress and the presence of inflammation disturb iron management in athletes during intense training. However, little is known about the mechanisms regulating iron levels in athletes during training periods with low training loads. In the current study, we analyzed the effect of an acute exercise on early responses of iron and iron regulatory proteins at the end of such training periods.

Methods

The study was performed at the end of competitive phase of training. A total of 27 trained female basketball players were included in the study after application of the inclusion/exclusion criteria. The participants performed an incremental exercise on a treadmill. Blood samples were taken before the test, immediately after exercise, and after 3 h of restitution. Parameters, such as interleukin (IL) 6, hepcidin, ferritin, transferrin, hemopexin, and lactoferrin levels, total iron-biding capacity (TIBC), unsaturated iron-biding capacity (UIBC) were determined by using appropriate biochemical tests.

Results

The level of iron increased significantly after exercise, and then decreased within next 3 h restitution. Except for iron levels, only TIBC levels significantly increased after exercise and decreased to baseline level during rest period. No significant changes in the levels of hepcidin, IL-6, and other proteins related to the iron homeostasis were observed.

Conclusions

The increases in iron level after acute exercise is short-term and transient and appear to have been insufficient to induce the acute systemic effects in rested athletes.

Involvement of G-CSF, IL-6, and cortisol in transient neutrophilia after marathon races

OBJECTIVES

The aim of this study was to clarify the mechanisms of the transient increase in neutrophils after running standard marathon races by measurement of cytokines involved in the production and survival of neutrophils, and cortisol.

METHODS

Fourteen male runners who participated in the Hokkaido Marathon, which is the sole marathon race held in summer in Japan, and finished the standard marathon were analyzed sequentially from the start until a maximum of 8 days after the finish.

RESULTS

Neutrophilia was observed in all runners just after they reached the goal (mean neutrophils: 13 226/μL). IL-6, G-CSF, and cortisol, but not GM-CSF, increased at the same time. Time-course studies with complete blood counts, biochemical markers, cytokines, and cortisol showed transient increases in neutrophils, monocytes, myoglobin, high-sensitivity C-reactive protein (hsCRP), G-CSF, IL-6, and cortisol. The increase in hsCRP was delayed 6 hours from the first increase in neutrophils. Correlations were observed between the neutrophil count and G-CSF, IL-6, and cortisol (G-CSF; r = .667, IL-6; r = .667, cortisol; r = .623).

CONCLUSION

These results suggest that G-CSF is directly involved, and IL-6 is involved via cortisol in the transient neutrophilia that occurs after marathon races.

Association of Serum Hepcidin Levels with Aerobic and Resistance Exercise: A Systematic Review

Background: Prevalence of iron deficiency is commonly reported among athletic population groups. It impairs physical performance due to insufficient oxygen delivery to target organs and low energy production. This is due to the high demand of exercise on oxygen delivery for systemic metabolism by the erythrocytes in the blood. Hepcidin, the key regulator of iron homeostasis, decreases to facilitate iron efflux into the circulation during enhanced erythropoiesis. However, acute anaemia of exercise is caused by increased hepcidin expression that is induced by stress and inflammatory signal. The study aimed to systematically review changes in serum hepcidin levels during resistance and aerobic exercise programmes. Methods: A systemic literature search from 2010 to April 2020 across seven databases comprised of Cochrane library, PubMed, Web of Science, Scopus, Embase, MEDLINE, and OpenGrey. The primary outcome was increased or decreased serum hepcidin from baseline after the exercise activity. Risks of bias were evaluated by using the National Institutes of Health (NIH) for quality assessment of before and after different exercise programmes. Results: Overall, twenty-three studies met the inclusion criteria. Out of the 23 studies, 16 studies reported significantly exercise-induced serum hepcidin elevation. Of the 17 studies that evaluated serum interleukin (IL)-6 levels, 14 studies showed significant exercise-induced serum IL-6 elevation. Changes in exercise-induced serum hepcidin and IL-6 levels were similar in both resistance and endurance exercise. Significant correlations were observed between post-exercise hepcidin and baseline ferritin levels (r = 0.69, p < 0.05) and between post-exercise hepcidin and post-exercise IL-6 (r = 0.625, p < 0.05). Conclusion: Resistance and endurance training showed significant increase in serum hepcidin and IL-6 levels in response to exercise. Baseline ferritin and post-exercise IL-6 elevation are key determining factors in the augmentation of hepcidin response to exercise.

The Effect of Vitamin D3 Supplementation on Hepcidin, Iron, and IL-6 Responses after a 100 km Ultra-Marathon

Deficiencies in iron and vitamin D are frequently observed in athletes. Therefore, we examined whether different baseline vitamin D₃ levels have any impact on post-exercise serum hepcidin, IL-6 and iron responses in ultra-marathon runners. In this randomized control trial, the subjects (20 male, amateur runners, mean age 40.75 ± 7.15 years) were divided into two groups: experimental (VD) and control (CON). The VD group received vitamin D₃ (10,000 UI/day) and the CON group received a placebo for two weeks before the run. Venous blood samples were collected on three occasions-before the run, after the 100 km ultra-marathon and 12 h after the run-to measure iron metabolism indicators, hepcidin, and IL-6 concentration. After two weeks of supplementation, the intervention group demonstrated a higher level of serum 25(OH)D than the CON group (27.82 ± 5.8 ng/mL vs. 20.41 ± 4.67 ng/mL; p < 0.05). There were no differences between the groups before and after the run in the circulating hepcidin and IL-6 levels. The decrease in iron concentration immediately after the 100-km ultra-marathon was smaller in the VD group than CON (p < 0.05). These data show that various vitamin D₃ status can affect the post-exercise metabolism of serum iron.

Influence of physical training on erythrocyte concentrations of iron, phosphorus and magnesium

BACKGROUND

The present study aimed to determine changes occurring in the erythrocyte concentrations of Iron (Fe), Magnesium (Mg) and Phosphorous (P) of subjects with different levels of physical training living in the same area of Extremadura (Spain).

METHODS

Thirty sedentary subjects (24.34 ± 3.02 years) without sports practice and a less active lifestyle, formed the control group (CG); 24 non-professional subjects (23.53 ± 1.85 years), who perform between 4 and 6 h/week of moderate sports practice without any performance objective and without following systematic training formed the group of subjects with a moderate level of training (MTG), and 22 professional cyclists (23.29 ± 2.73 years) at the beginning of their sports season, who performed more than 20 h/week of training, formed the high-level training group (HTG). Erythrocyte samples from all subjects were collected and frozen at - 80 °C until analysis. Erythrocyte analysis of Fe, Mg and P was performed by inductively coupled plasma mass spectrometry (ICP-MS). All results are expressed in μg/g Hb.

RESULTS

The results showed that there were statistically significant lower concentrations of erythrocyte Fe, Mg and P in MTG and HTG than CG. All parameters (Fe, Mg and P concentrations in erythrocytes) correlated inversely with physical training.

CONCLUSIONS

Physical exercise produces a decrease in erythrocyte concentrations of Fe, Mg and P. This situation could cause alterations in the performance of athletes given the importance of these elements. For this reason, we recommend an erythrocyte control at the beginning, and during the training period, to avoid harmful deficits.

Single versus Split Dose of Iron Optimizes Hemoglobin Mass Gains at 2106 m Altitude

PURPOSE

To determine if a single versus a split equivalent daily dose of elemental iron was superior for hemoglobin mass (Hbmass) gains at altitude while minimizing gastrointestinal (GI) discomfort.

METHODS

Twenty-four elite runners attended a 3.1 ± 0.3 wk training camp (Flagstaff, AZ; 2106 m). A two-group design, randomized and stratified to baseline Hbmass, sex, and ferritin (>30 μ·L), was implemented daily as: 1) single dose of 1 × 200 mg (PM only, SINGLE) versus 2) split dose of 2 × 100 mg (AM and PM; SPLIT) elemental iron (ferrous fumarate). The Hbmass and venipuncture assessments were completed upon arrival and departure (±2 d) from camp for ferritin, hepcidin, and erythroferrone (ERFE) concentrations. Validated food frequency, GI distress, menstrual blood loss (MBL) and training questionnaires were implemented throughout. Univariate analysis was used to compare Hbmass, with baseline ferritin, dietary iron intake, MBL, and training volume used as covariates.

RESULTS

Both conditions increased Hbmass from baseline (P < 0.05), with SINGLE (867.3 ± 47.9 g) significantly higher than SPLIT (828.9 ± 48.9 g) (P = 0.048). The GI scores were worse in SINGLE for weeks 1 and 2 combined (SINGLE, 18.0 ± 6.7 points; SPLIT, 11.3 ± 6.9 points; P = 0.025); however, GI scores improved by week 3, resulting in no between-group differences (P = 0.335). Hepcidin significantly decreased over time (P = 0.043) in SINGLE, with a nonsignificant decrease evident in SPLIT (~22%). ERFE significantly decreased in both groups (~28.5%; P < 0.05). No between-group differences existed for ERFE, hepcidin, food frequency, MBL, or daily training outcomes (P > 0.05).

CONCLUSIONS

A single nightly 200-mg dose of elemental iron was superior to a split dose for optimizing Hbmass changes at altitude in runners over an approximately 3-wk training camp.

Sport Nutrigenomics: Personalized Nutrition for Athletic Performance

An individual's dietary and supplement strategies can influence markedly their physical performance. Personalized nutrition in athletic populations aims to optimize health, body composition, and exercise performance by targeting dietary recommendations to an individual's genetic profile. Sport dietitians and nutritionists have long been adept at placing additional scrutiny on the one-size-fits-all general population dietary guidelines to accommodate various sporting populations. However, generic "one-size-fits-all" recommendations still remain. Genetic differences are known to impact absorption, metabolism, uptake, utilization and excretion of nutrients and food bioactives, which ultimately affects a number of metabolic pathways. Nutrigenomics and nutrigenetics are experimental approaches that use genomic information and genetic testing technologies to examine the role of individual genetic differences in modifying an athlete's response to nutrients and other food components. Although there have been few randomized, controlled trials examining the effects of genetic variation on performance in response to an ergogenic aid, there is a growing foundation of research linking gene-diet interactions on biomarkers of nutritional status, which impact exercise and sport performance. This foundation forms the basis from which the field of sport nutrigenomics continues to develop. We review the science of genetic modifiers of various dietary factors that impact an athlete's nutritional status, body composition and, ultimately athletic performance.

Changes in iron metabolism during prolonged repeated walking exercise in middle-aged men and women

Purpose

The aim of the present study was to assess the effect of prolonged and repeated exercise on iron metabolism in middle-aged adults and to compare differences between sexes.

Methods

50 male (58.9 ± 9.9 year) and 48 female (50.9 ± 11.2 year) individuals were monitored on 4 consecutive days at which they walked on average 8 h and 44 min per day at a self-determined pace. Blood samples were collected 1 or 2 days prior to the start of the exercise (baseline) and every day immediately post-exercise. Samples were analysed for iron, ferritin, haemoglobin, and haptoglobin concentrations.

Results

Plasma iron decreased across days, while ferritin increased across days (both p < 0.001). Haptoglobin showed a decrease (p < 0.001) after the first day and increased over subsequent days (p < 0.001). Haemoglobin did not change after the first day, but increased during subsequent days (p < 0.05). At baseline, 8% of the participants had iron concentrations below minimum reference value (10 µmol/L), this increased to 43% at day 4. There was an interaction between sex and exercise days on iron (p = 0.028), ferritin (p < 0.001) and haemoglobin levels (p = 0.004), but not on haptoglobin levels.

Conclusion

This study showed decreases in iron, increases in ferritin, a decrease followed by increases in haptoglobin and no change followed by increases in haemoglobin. This is most likely explained by (foot strike) haemolysis, inflammation, and sweat and urine losses. These processes resulted in iron levels below minimum reference value in a large number of our participants.

Effects of an Acute Exercise Bout on Serum Hepcidin Levels

Iron deficiency is a frequent and multifactorial disorder in the career of athletes, particularly in females. Exercise-induced disturbances in iron homeostasis produce deleterious effects on performance and adaptation to training; thus, the identification of strategies that restore or maintain iron homeostasis in athletes is required. Hepcidin is a liver-derived hormone that degrades the ferroportin transport channel, thus reducing the ability of macrophages to recycle damaged iron, and decreasing iron availability. Although it has been suggested that the circulating fraction of hepcidin increases during early post-exercise recovery (~3 h), it remains unknown how an acute exercise bout may modify the circulating expression of hepcidin. Therefore, the current review aims to determine the post-exercise expression of serum hepcidin in response to a single session of exercise. The review was carried out in the Dialnet, Elsevier, Medline, Pubmed, Scielo and SPORTDiscus databases, using hepcidin (and “exercise” or “sport” or “physical activity”) as a strategy of search. A total of 19 articles were included in the review after the application of the inclusion/exclusion criteria. This search found that a single session of endurance exercise (intervallic or continuous) at moderate or vigorous intensity (60–90% VO_2peak) stimulates an increase in the circulating levels of hepcidin between 0 h and 6 h after the end of the exercise bout, peaking at ~3 h post-exercise. The magnitude of the response of hepcidin to exercise seems to be dependent on the pre-exercise status of iron (ferritin) and inflammation (IL-6). Moreover, oxygen disturbances and the activation of a hypoxia-induced factor during or after exercise may stimulate a reduction of hepcidin expression. Meanwhile, cranberry flavonoids supplementation promotes an anti-oxidant effect that may facilitate the post-exercise expression of hepcidin. Further studies are required to explore the effect of resistance exercise on hepcidin expression.

Iron balance and iron supplementation for the female athlete: A practical approach

Maintaining a positive iron balance is essential for female athletes to avoid the effects of iron deficiency and anaemia and to maintain or improve performance. A major function of iron is in the production of the oxygen and carbon dioxide carrying molecule, haemoglobin, via erythropoiesis. Iron balance is under the control of a number of factors including the peptide hormone hepcidin, dietary iron intake and absorption, environmental stressors (e.g. altitude), exercise, menstrual blood loss and genetics. Menstruating females, particularly those with heavy menstrual bleeding are at an elevated risk of iron deficiency. Haemoglobin concentration [Hb] and serum ferritin (sFer) are traditionally used to identify iron deficiency, however, in isolation these may have limited value in athletes due to: (1) the effects of fluctuations in plasma volume in response to training or the environment on [Hb], (2) the influence of inflammation on sFer and (3) the absence of sport, gender and individually specific normative data. A more detailed and longitudinal examination of haematology, menstrual cycle pattern, biochemistry, exercise physiology, environmental factors and training load can offer a superior characterisation of iron status and help to direct appropriate interventions that will avoid iron deficiency or iron overload. Supplementation is often required in iron deficiency; however, nutritional strategies to increase iron intake, rest and descent from altitude can also be effective and will help to prevent future iron deficient episodes. In severe cases or where there is a time-critical need, such as major championships, iron injections may be appropriate.

67Ga as a biosensor of iron needs in different organs: Study performed on male and female rats subjected to iron deficiency and exercise

The aim of the present study was to determine the iron needs in different organs and tissues using ⁶⁷Ga as a biosensor in males and females rats subjected to iron deficiency (ID) and voluntary exercise (EX). ⁶⁷Ga citrate was injected i.p. to female and male Wistar rats (n=5/sex/group). Groups: Control (sedentary conditions), Control+EX, ID and ID+EX. To determine the ⁶⁷Ga uptake, samples from the following regions of interest (ROIs) were extracted 12h post-injection: blood, liver, gonads, bone marrow, heart, adrenal glands, skeletal muscle, stomach, kidney, eyeball, sciatic nerve, small intestine and peritoneum. The total ⁶⁷Ga uptake was 412% higher in ID subjects than in control subjects, being 1011% higher in ID-males than ID-females. In ID-females, the ROIs with the greater ⁶⁷Ga uptake were blood, kidney and bone marrow, while in ID-males they were sciatic nerve, eyeball and adrenals, which demonstrates that the biodistribution differed between sexes in sedentary conditions but when subjected to EX, the biodistribution was similar in each sex group although females had a greater ⁶⁷Ga uptake. In ID+EX subjects, the ROIs that showed the highest uptake were sciatic nerve, eyeball and adrenal glands. Using ⁶⁷Ga as a biosensor, it is possible to identify the needs of iron that each organ requires to perform their functions in normal physiological conditions. In addition, a higher or lower ⁶⁷Ga uptake in a specific organ may indicate its malfunction or show damage.

Recent Advances in Iron Metabolism: Relevance for Health, Exercise, and Performance

Iron is necessary for physiological processes essential for athletic performance, such as oxygen transport, energy production, and cell division. However, an excess of "free" iron is toxic because it produces reactive hydroxyl radicals that damage biological molecules, thus leading to cell and tissue injury. Therefore, iron homeostasis is strictly regulated; and in recent years, there have been important advancements in our knowledge of the underlying processes. Hepcidin is the central regulator of systemic iron homeostasis and exerts its function by controlling the presence of the iron exporter ferroportin on the cell membrane. Hepcidin binding induces ferroportin degradation, thus leading to cellular iron retention and decreased levels of circulating iron. As iron is required for hemoglobin synthesis, the tight link between erythropoiesis and iron metabolism is particularly relevant to sports physiology. The iron needed for hemoglobin synthesis is ensured by inhibiting hepcidin to increase ferroportin activity and iron availability and hence to make certain that efficient blood oxygen transport occurs for aerobic exercise. However, hepcidin expression is also affected by exercise-associated conditions, such as iron deficiency, anemia or hypoxia, and, particularly, inflammation, which can play a role in the pathogenesis of sports anemia. Here, we review recent advances showing the relevance of iron for physical exercise and athletic performance. Low body iron levels can cause anemia and thus limit the delivery of oxygen to exercising muscle, but tissue iron deficiency may also affect performance by, for example, hampering muscle oxidative metabolism. Accordingly, a hemoglobin-independent effect of iron on exercise capacity has been demonstrated in animal models and humans. Here, we review recent advances showing the relevance of iron for physical exercise and athletic performance.

Timing of post-exercise carbohydrate ingestion: influence on IL-6 and hepcidin responses

PURPOSE

Carbohydrate ingestion prior and during exercise attenuates exercise-induced interleukin-6. This investigation examined if an analogous effect was evident for interleukin-6 and hepcidin response when carbohydrates were ingested post-exercise.

METHODS

In a crossover design, 11 well-trained endurance athletes completed two experimental trials. Participants completed an 8 × 3 min interval running session at 85 % vVO2peak followed by 5 h of monitored recovery. During this period, participants were provided with two 1.2 g kg(-1) carbohydrate beverages at either an early feeding time (immediately post-exercise and 2 h post-exercise) or delayed feeding time (2 h post-exercise and 4 h post-exercise). Venous blood samples were collected pre-, immediately post-, 3 and 5 h post-exercise. Samples were analysed for Interleukin-6, serum iron, serum ferritin and hepcidin.

RESULTS

Interleukin-6 was significantly elevated (p = 0.004) immediately post-exercise compared to baseline for both trials. Hepcidin levels were significantly elevated at 3 h post-exercise (p = 0.001) and 5 h post-exercise (p = 0.002) compared to baseline levels in both trials, with no significant difference between the two conditions and any time point. Serum iron was significantly increased from baseline to immediately post-exercise (p = 0.001) for both trials, with levels decreasing by 3 h (p = 0.025) and 5 h post-exercise (p = 0.001). Serum ferritin levels increased immediately post-exercise compared to baseline (p = 0.006) in both conditions.

CONCLUSIONS

The timing and ingestion of post-exercise carbohydrate ingestion do not appear to impact post-exercise interleukin-6 and hepcidin responses; this is likely a result of the interval running task inducing an inflammatory response and subsequent up-regulation of hepcidin.

Physical activity - an important preanalytical variable

The concentration of several biochemical and hematological biomarkers is strongly influenced by a number of preanalytical variables. Several lines of evidence attest that short, middle, and long-term exercise, as well as the relative intensity of physical effort (from mild to strenuous), may influence a broad array of laboratory variables. The amount of extracellular release and clearance from blood of most of these biomarkers is markedly influenced by the biological characteristics of the molecule(s), level of training, type, intensity and duration of exercise, and time of recovery after training. It is hence noteworthy that test results that fall outside the conventional reference ranges in athletes not only may reflect the presence of a given disease, but may frequently mirror an adaptation to regular training or changes that have occurred during and/or following strenuous exercise, and which should be clearly acknowledged to prevent misinterpretation of laboratory data. The aim of this narrative review is to provide an update about the most significant changes of some biochemical and hematological biomarkers in response to physical exercise, for appropriate interpretation of these changes in the context of physically active subjects.

Influence of post-exercise hypoxic exposure on hepcidin response in athletes

PURPOSE

To assess the influence of a simulated altitude exposure (~2,900 m above sea level) for a 3 h recovery period following intense interval running on post-exercise inflammation, serum iron, ferritin, erythropoietin, and hepcidin response.

METHODS

In a cross-over design, ten well-trained male endurance athletes completed two 8 × 3 min interval running sessions at 85 % of their maximal aerobic velocity on a motorized treadmill, before being randomly assigned to either a hypoxic (HYP: F IO2 ~0.1513) or a normoxic (NORM: F IO2 0.2093) 3 h recovery period. Venous blood was collected pre- and immediately post-exercise, and after 3 and 24 h of recovery. Blood was analyzed for interleukin-6, serum iron, ferritin, erythropoietin, and hepcidin.

RESULTS

Interleukin-6 was significantly elevated (p < 0.01) immediately post-exercise compared to baseline (NORM: 1.08 ± 0.061 to 3.12 ± 1.80) (HYP: 1.32 ± 0.86 to 2.99 ± 2.02), but was not different between conditions. Hepcidin levels were significantly elevated (p < 0.01) at 3 h post-exercise for both conditions when compared to baseline (NORM: 3.25 ± 1.23 to 7.40 ± 4.00) (HYP: 3.24 ± 1.94 to 5.42 ± 3.20), but were significantly lower (p < 0.05) in the HYP trial compared to NORM. No significant differences existed between HYP and NORM for erythropoietin, serum iron, or ferritin.

CONCLUSION

Simulated altitude exposure (~2,900 m) for 3 h following intense interval running attenuates the peak hepcidin levels recorded at 3 h post-exercise. Consequently, a hypoxic recovery after exercise may be useful for athletes with compromised iron status to potentially increase acute dietary iron absorption.