Live high, train low - influence on resting and post-exercise hepcidin levels

The relationship between hemoglobin and [Formula: see text]: A systematic review and meta-analysis

OBJECTIVE

There is widespread agreement about the key role of hemoglobin for oxygen transport. Both observational and interventional studies have examined the relationship between hemoglobin levels and maximal oxygen uptake ([Formula: see text]) in humans. However, there exists considerable variability in the scientific literature regarding the potential relationship between hemoglobin and [Formula: see text]. Thus, we aimed to provide a comprehensive analysis of the diverse literature and examine the relationship between hemoglobin levels (hemoglobin concentration and mass) and [Formula: see text] (absolute and relative [Formula: see text]) among both observational and interventional studies.

METHODS

A systematic search was performed on December 6th, 2021. The study procedures and reporting of findings followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Article selection and data abstraction were performed in duplicate by two independent reviewers. Primary outcomes were hemoglobin levels and [Formula: see text] values (absolute and relative). For observational studies, meta-regression models were performed to examine the relationship between hemoglobin levels and [Formula: see text] values. For interventional studies, meta-analysis models were performed to determine the change in [Formula: see text] values (standard paired difference) associated with interventions designed to modify hemoglobin levels or [Formula: see text]. Meta-regression models were then performed to determine the relationship between a change in hemoglobin levels and the change in [Formula: see text] values.

RESULTS

Data from 384 studies (226 observational studies and 158 interventional studies) were examined. For observational data, there was a positive association between absolute [Formula: see text] and hemoglobin levels (hemoglobin concentration, hemoglobin mass, and hematocrit (P<0.001 for all)). Prespecified subgroup analyses demonstrated no apparent sex-related differences among these relationships. For interventional data, there was a positive association between the change of absolute [Formula: see text] (standard paired difference) and the change in hemoglobin levels (hemoglobin concentration (P<0.0001) and hemoglobin mass (P = 0.006)).

CONCLUSION

These findings suggest that [Formula: see text] values are closely associated with hemoglobin levels among both observational and interventional studies. Although our findings suggest a lack of sex differences in these relationships, there were limited studies incorporating females or stratifying results by biological sex.

Iron Status and Physical Performance in Athletes

Iron is an important mineral in the body, essential for muscle function and oxygen transport. Adequate levels of iron in the blood are necessary for athletes, as iron-deficiency anemia can reduce physical performance. Several studies have investigated iron status and supplementation in iron-deficient athletes, and determined how physical strain can change iron balance and markers related to iron status. The question of how to influence and optimize iron status, as well as other markers that can affect iron metabolism, has been less thoroughly investigated. Therefore, the aim of this review is to take a closer look at the importance of iron values, iron markers, and factors that can change iron metabolism for physical performance and the extent to which physical performance can be influenced in a positive or negative way. A systematic search of the PubMed database was performed, with the use of « iron» or «iron deficiency» or «hemoglobin» AND «athletes» AND «athletic performance» as a strategy of the search. After the search, 11 articles were included in the review after the application of inclusion and exclusion criteria. Major findings include that iron supplementation had the best effect in athletes with the lowest iron status, and effects on physical performance were mostly achieved in those who were originally in a deficit. Iron supplementation could be beneficial for optimal erythropoietic response during altitude training, even in athletes with normal iron stores at baseline, but should be performed with caution. Alteration of the hepcidin response can affect the use of existing iron stores for erythropoiesis. Energy intake, and the amount of carbohydrates available, may have an impact on the post-exercise hepcidin response. Optimal vitamin D and B12 levels can possibly contribute to improved iron status and, hence, the avoidance of anemia.

A contemporary understanding of iron metabolism in active premenopausal females

Iron metabolism research in the past decade has identified menstrual blood loss as a key contributor to the prevalence of iron deficiency in premenopausal females. The reproductive hormones estrogen and progesterone influence iron regulation and contribute to variations in iron parameters throughout the menstrual cycle. Despite the high prevalence of iron deficiency in premenopausal females, scant research has investigated female-specific causes and treatments for iron deficiency. In this review, we provide a comprehensive discussion of factors that influence iron status in active premenopausal females, with a focus on the menstrual cycle. We also outline several practical guidelines for monitoring, diagnosing, and treating iron deficiency in premenopausal females. Finally, we highlight several areas for further research to enhance the understanding of iron metabolism in this at-risk population.

Wellness Forecasting by External and Internal Workloads in Elite Soccer Players: A Machine Learning Approach

Training for success has increasingly become a balance between maintaining high performance standards and avoiding the negative consequences of accumulated fatigue. The aim of this study is to develop a big data analytics framework to predict players’ wellness according to the external and internal workloads performed in previous days. Such a framework is useful for coaches and staff to simulate the players’ response to scheduled training in order to adapt the training stimulus to the players’ fatigue response. 17 players competing in the Italian championship (Serie A) were recruited for this study. Players’ Global Position System (GPS) data was recorded during each training and match. Moreover, every morning each player has filled in a questionnaire about their perceived wellness (WI) that consists of a 7-point Likert scale for 4 items (fatigue, sleep, stress, and muscle soreness). Finally, the rate of perceived exertion (RPE) was used to assess the effort performed by the players after each training or match. The main findings of this study are that it is possible to accurately estimate players’ WI considering their workload history as input. The machine learning framework proposed in this study is useful for sports scientists, athletic trainers, and coaches to maximise the periodization of the training based on the physiological requests of a specific period of the season.

Hepcidin as a Prospective Individualized Biomarker for Individuals at Risk of Low Energy Availability

Hepcidin, a peptide hormone with an acknowledged evolutionary function in iron homeostasis, was discovered at the turn of the 21st century. Since then, the implications of increased hepcidin activity have been investigated as a potential advocate for the increased risk of iron deficiency in various health settings. Such implications are particularly relevant in the sporting community where peaks in hepcidin postexercise (∼3-6 hr) are suggested to reduce iron absorption and recycling, and contribute to the development of exercise-induced iron deficiency in athletes. Over the last decade, hepcidin research in sport has focused on acute and chronic hepcidin activity following single and repeated training blocks. This research has led to investigations examining possible methods to attenuate postexercise hepcidin expression through dietary interventions. The majority of macronutrient dietary interventions have focused on manipulating the carbohydrate content of the diet in an attempt to determine the health of athletes adopting the low-carbohydrate or ketogenic diets, a practice that is a growing trend among endurance athletes. During the process of these macronutrient dietary intervention studies, an observable coincidence of increased cumulative hepcidin activity to low energy availability has emerged. Therefore, this review aims to summarize the existing literature on nutritional interventions on hepcidin activity, thus, highlighting the link of hepcidin to energy availability, while also making a case for the use of hepcidin as an individualized biomarker for low energy availability in males and females.

The effects of normoxic endurance exercise on erythropoietin (EPO) production and the impact of selective β1 and non-selective β1 + β2 adrenergic receptor blockade

PURPOSE

Habitual endurance exercise results in increased erythropoiesis, which is primarily controlled by erythropoietin (EPO), yet studies demonstrating upregulation of EPO via a single bout of endurance exercise have been equivocal. This study compares the acute EPO response to 30 min of high versus 90 min of moderate-intensity endurance exercise and whether that response can be upregulated via selective adrenergic receptor blockade.

METHODS

Using a counterbalanced, cross-over design, fifteen participants (age 28 ± 8) completed two bouts of running (30-min, high intensity vs 90-min, moderate intensity) matched for overall training stress. A separate cohort of fourteen participants (age 31 ± 6) completed three bouts of 30-min high-intensity cycling after ingesting the preferential β₁-adrenergic receptor (AR) antagonist bisoprolol, the non-preferential β₁ + β₂ antagonist nadolol or placebo. Venous blood was collected before, during, and after exercise, and serum EPO levels were determined by ELISA.

RESULTS

No detectable EPO response was observed during or after high intensity running, however, in the moderate-intensity trial EPO was significantly elevated at both during-exercise timepoints (+ 6.8% ± 2.3% at 15 min and + 8.7% ± 2.2% at 60 min). No significant change in EPO was observed post-cycling or between the trials involving βAR blockade.

CONCLUSION

Neither training mode (running or cycling), nor beta-blockade significantly influenced the EPO response to 30 min of high-intensity exercise, however, 90 min of moderate-intensity running elevated EPO during exercise, returning to baseline immediately post-exercise. Identifying the optimal mode, duration and intensity required to evoke an EPO response to exercise may help tailor exercise prescriptions designed to maximize EPO response for both performance and clinical applications.

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.

Erythroferrone structure, function, and physiology: Iron homeostasis and beyond

Erythroferrone (ERFE) is the main erythroid regulator of hepcidin, the homeostatic hormone controlling plasma iron levels and total body iron. When the release of erythropoietin from the kidney stimulates the production of new red blood cells, it also increases the synthesis of ERFE in bone marrow erythroblasts. Increased ERFE then suppresses hepcidin synthesis, thereby mobilizing cellular iron stores for use in heme and hemoglobin synthesis. Recent mechanistic studies have shown that ERFE suppresses hepcidin transcription by inhibiting bone morphogenetic protein signaling in hepatocytes. In ineffective erythropoiesis, pathological overproduction of ERFE by an expanded population of erythroblasts suppresses hepcidin and causes iron overload, even in non-transfused patients. ERFE may be a useful biomarker of ineffective erythropoiesis and an attractive target for treating its systemic effects.

Nutrition and Altitude: Strategies to Enhance Adaptation, Improve Performance and Maintain Health: A Narrative Review

Training at low to moderate altitudes (~ 1600-2400 m) is a common approach used by endurance athletes to provide a distinctive environmental stressor to augment training stimulus in the anticipation of increasing subsequent altitude- and sea-level-based performance. Despite some scientific progress being made on the impact of various nutrition-related changes in physiology and associated interventions at mountaineering altitudes (> 3000 m), the impact of nutrition and/or supplements on further optimization of these hypoxic adaptations at low-moderate altitudes is only an emerging topic. Within this narrative review we have highlighted six major themes involving nutrition: altered energy availability, iron, carbohydrate, hydration, antioxidant requirements and various performance supplements. Of these issues, emerging data suggest that particular attention be given to the potential risk for poor energy availability and increased iron requirements at the altitudes typical of elite athlete training (~ 1600-2400 m) to interfere with optimal adaptations. Furthermore, the safest way to address the possible increase in oxidative stress associated with altitude exposure is via the consumption of antioxidant-rich foods rather than high-dose antioxidant supplements. Meanwhile, many other important questions regarding nutrition and altitude training remain to be answered. At the elite level of sport where the differences between winning and losing are incredibly small, the strategic use of nutritional interventions to enhance the adaptations to altitude training provides an important consideration in the search for optimal performance.

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.

No effect of supplemented heat stress during an acute endurance exercise session in hypoxia on hepcidin regulation

Hepcidin is a novel factor for iron deficiency in athletes, which is suggested to be regulated by interleukin-6 (IL-6) or erythropoietin (EPO).

PURPOSE

The purpose of the present study was to compare endurance exercise-induced hepcidin elevation among "normoxia", "hypoxia" and "combined heat and hypoxia".

METHODS

Twelve males (21.5 ± 0.3 years, 168.1 ± 1.2 cm, 63.6 ± 2.0 kg) participated in the present study. They performed 60 min of cycling at 60% of [Formula: see text] in either "heat and hypoxia" (HHYP; F_iO₂ 14.5%, 32 °C), "hypoxia" (HYP; F_iO₂ 14.5%, 23 °C) or "normoxia" (NOR; F_iO₂ 20.9%, 23 °C). After completing the exercise, participants remained in the prescribed conditions for 3 h post-exercise. Blood samples were collected before, immediately and 3 h after exercise.

RESULTS

Plasma IL-6 level significantly increased immediately after exercise (P < 0.05), with no significant difference among the trials. A significant elevation in serum EPO was observed 3 h after exercise in hypoxic trials (HHYP and HYP, P < 0.05), with no significant difference between HHYP and HYP. Serum hepcidin level increased 3 h after exercise in all trials (NOR, before 18.3 ± 3.9 and post180 31.2 ± 6.3 ng/mL; HYP, before 13.5 ± 2.5 and post180 23.3 ± 3.6 ng/mL, HHYP; before 15.8 ± 3.3 and post180 31.4 ± 5.3 ng/mL, P < 0.05). However, there was no significant difference among the trials during post-exercise.

CONCLUSION

Endurance exercise in "combined heat and hypoxia" did not exacerbate exercise-induced hepcidin elevation compared with the same exercise in "hypoxia" or "normoxia".

Increased Hepcidin Levels During a Period of High Training Load Do Not Alter Iron Status in Male Elite Junior Rowers

The liver-derived hormone hepcidin plays a key role in iron metabolism by mediating the degradation of the iron export protein ferroportin 1 (FPN1). Circulating levels of hepcidin and the iron storage protein ferritin are elevated during the recovery period after acute endurance exercise, which can be interpreted as an acute phase reaction to intense exercise with far-reaching consequences for iron metabolism and homeostasis. Since absolute and functional iron deficiency (ID) potentially lead to a loss of performance and well-being, it is surprising that the cumulative effects of training stress on hepcidin levels and its interplay with cellular iron availability are not well described. Therefore, the aim of this study was to determine serum levels of hepcidin at six time points during a 4-week training camp of junior world elite rowers preparing for the world championships and to relate the alterations in training load to overall iron status determined by serum ferritin, transferrin, iron, and soluble transferrin receptor (sTfR). Serum hepcidin levels increased significantly (p = 0.02) during the initial increase in training load (23.24 ± 2.43 ng/ml) at day 7 compared to the start of training camp (11.47 ± 3.92 ng/ml) and turned back on day 13 (09.51 ± 3.59 ng/ml) already, meeting well the entrance level of hepcidin at day 0. Serum ferritin was significantly higher at day 7 compared to all other timepoints with exception of the subsequent time point at day 13 reflecting well the time course pattern of hepcidin. Non-significant changes between training phases were found for serum iron, transferrin, and sTfR levels as well as for transferrin saturation, and ferritin-index (sTfR/log ferritin). Our findings indicate that hepcidin as well as ferritin, both representing acute phase proteins, are sensitive to initial increases in training load. Erythropoiesis was unaffected by iron compartmentalization through hepcidin. We conclude that hepcidin is sensitive to rigorous changes in training load in junior world elite rowers without causing short-term alterations in functional iron homeostasis.

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.

Iron insufficiency diminishes the erythropoietic response to moderate altitude exposure

The effects of iron stores and supplementation on erythropoietic responses to moderate altitude in endurance athletes were examined. In a retrospective study, red cell compartment volume (RCV) responses to 4 wk at 2,500 m were assessed in athletes with low ( n = 9, ≤20 and ≤30 ng/mL for women and men, respectively) and normal ( n = 10) serum ferritin levels ([Ferritin]) without iron supplementation. In a subsequent prospective study, the same responses were assessed in athletes ( n = 26) with a protocol designed to provide sufficient iron before and during identical altitude exposure. The responses to a 4-wk training camp at sea level were assessed in another group of athletes ( n = 13) as controls. RCV and maximal oxygen uptake (V̇o2max) were determined at sea level before and after intervention. In the retrospective study, athletes with low [Ferritin] did not increase RCV (27.0 ± 2.9 to 27.5 ± 3.8 mL/kg, mean ± SD, P = 0.65) or V̇o2max (60.2 ± 7.2 to 62.2 ± 7.5 mL·kg−1·min−1, P = 0.23) after 4 wk at altitude, whereas athletes with normal [Ferritin] increased both (RCV: 27.3 ± 3.1 to 29.8 ± 2.4 mL/kg, P = 0.002; V̇o2max: 62.0 ± 3.1 to 66.2 ± 3.7 mL·kg−1·min−1, P = 0.003). In the prospective study, iron supplementation normalized low [Ferritin] observed in athletes exposed to altitude ( n = 14) and sea level ( n = 6) before the altitude/sea-level camp and maintained [Ferritin] within normal range in all athletes during the camp. RCV and V̇o2max increased in the altitude group but remained unchanged in the sea-level group. Finally, the increase in RCV correlated with the increase in V̇o2max [( r = 0.368, 95% confidence interval (CI): 0.059–0.612, P = 0.022]. Thus, iron deficiency in athletes restrains erythropoiesis to altitude exposure and may preclude improvement in sea-level athletic performance.

NEW & NOTEWORTHY Hypoxic exposure increases iron requirements and utilization for erythropoiesis in athletes. This study clearly demonstrates that iron deficiency in athletes inhibits accelerated erythropoiesis to a sojourn to moderate high altitude and may preclude a potential improvement in sea-level athletic performance with altitude training. Iron replacement therapy before and during altitude exposure is important to maximize performance gains after altitude training in endurance athletes.

Characterizing the plasma metabolome during 14 days of live-high, train-low simulated altitude: A metabolomic approach

NEW FINDINGS

What is the central question of this study? Does 14 days of live-high, train-low simulated altitude alter an individual's metabolomic/metabolic profile? What is the main finding and its importance? This study demonstrated that ∼200 h of moderate simulated altitude exposure resulted in greater variance in measured metabolites between subject than within subject, which indicates individual variability during the adaptive phase to altitude exposure. In addition, metabolomics results indicate that altitude alters multiple metabolic pathways, and the time course of these pathways is different over 14 days of altitude exposure. These findings support previous literature and provide new information on the acute adaptation response to altitude.

ABSTRACT

The purpose of this study was to determine the influence of 14 days of normobaric hypoxic simulated altitude exposure at 3000 m on the human plasma metabolomic profile. For 14 days, 10 well-trained endurance runners (six men and four women; 29 ± 7 years of age) lived at 3000 m simulated altitude, accumulating 196.4 ± 25.6 h of hypoxic exposure, and trained at ∼600 m. Resting plasma samples were collected at baseline and on days 3 and 14 of altitude exposure and stored at -80°C. Plasma samples were analysed using liquid chromatography-high-resolution mass spectrometry to construct a metabolite profile of altitude exposure. Mass spectrometry of plasma identified 36 metabolites, of which eight were statistically significant (false discovery rate probability 0.1) from baseline to either day 3 or day 14. Specifically, changes in plasma metabolites relating to amino acid metabolism (tyrosine and proline), glycolysis (adenosine) and purine metabolism (adenosine) were observed during altitude exposure. Principal component canonical variate analysis showed significant discrimination between group means (P < 0.05), with canonical variate 1 describing a non-linear recovery trajectory from baseline to day 3 and then back to baseline by day 14. Conversely, canonical variate 2 described a weaker non-recovery trajectory and increase from baseline to day 3, with a further increase from day 3 to 14. The present study demonstrates that metabolomics can be a useful tool to monitor metabolic changes associated with altitude exposure. Furthermore, it is apparent that altitude exposure alters multiple metabolic pathways, and the time course of these changes is different over 14 days of altitude exposure.

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.

Postexercise serum hepcidin response to repeated sprint exercise under normoxic and hypoxic conditions

We determined the effects of repeated sprint exercise under normoxic and hypoxic conditions on serum hepcidin levels. Ten male athletes (age: 20.9 ± 0.3 years; height: 175.7 ± 6.0 cm; weight: 67.3 ± 6.3 kg) performed 2 exercise trials under normoxic (NOR; fraction of inspiratory oxygen (FiO₂): 20.9%) or hypoxic conditions (HYPO; FiO₂: 14.5%). The exercise consisted of 3 sets of 5 × 6 s of maximal pedaling (30-s rest periods between sprints, 10-min rest periods between sets). Blood samples were collected before exercise, immediately after exercise, and 1 and 3 h after exercise. Serum hepcidin levels were significantly elevated after exercise in both trials (both P < 0.01), with no significant difference between the trials. The postexercise blood lactate levels were significantly higher in the HYPO than the NOR (P < 0.05). Both trials caused similar increases in plasma interleukin-6 and serum iron levels (P < 0.001), with no significant difference between the trials. A significant interaction (trial × time) was apparent in terms of serum erythropoietin (EPO) levels (P = 0.003). The EPO level was significantly higher in the HYPO than the NOR at 3 h after exercise (P < 0.05). In conclusion, repeated sprint exercise significantly increased serum hepcidin levels to similar extent in 2 trials, despite differences in the inspired oxygen concentrations during both the exercise and the 3-h postexercise period.

Post-exercise serum hepcidin levels were unaffected by hypoxic exposure during prolonged exercise sessions

The purpose of the present study was to determine the influence of hypoxic exposure during prolonged endurance exercise sessions (79 min in total) on post-exercise hepcidin levels in trained male endurance athletes. Ten endurance athletes (mean ± standard deviation; height: 169.8 ± 7.1 cm, weight: 57.1 ± 5.0 kg) conducted two endurance exercise sessions under either a normobaric hypoxic condition [inspired O2 fraction (FiO2) = 14.5%] or a normoxic condition (FiO2 = 20.9%). Exercise consisted of 10 × 3 min running on a treadmill at 95% of maximal oxygen uptake ([Formula: see text]) with 60s of active rest at 60% of [Formula: see text]. After 10 min of rest, they subsequently performed 30 min of continuous running at 85% of [Formula: see text]. Running velocities were significantly lower in the HYPO than in the NOR (P < 0.0001). Exercise-induced blood lactate elevation was significantly greater in the HYPO (P < 0.01). There were significant increases in plasma interleukin-6, serum iron, and blood glucose levels after exercise, with no significant difference between the trials [interaction (trial × time) or main effect for trial, P > 0.05]. Serum hepcidin levels increased significantly 120 min after exercise (HYPO: from 10.7 ± 9.4 ng/mL to 15.8 ± 11.2 ng/mL; NOR: from 7.9 ± 4.7 ng/mL to 13.2 ± 7.9 ng/mL, P < 0.05), and no difference was observed between the trials. In conclusion, endurance exercise at lower running velocity in hypoxic conditions resulted in similar post-exercise hepcidin elevations as higher running velocity in normoxic conditions.

Reduced cancer mortality at high altitude: The role of glucose, lipids, iron and physical activity

Residency at high altitude (HA) demands adaptation to challenging environmental conditions with hypobaric hypoxia being the most important one. Epidemiological and experimental data suggest that chronic exposure to HA reduces cancer mortality and lowers prevalence of metabolic disorders like diabetes and obesity implying that adaption to HA modifies a broad spectrum of physiological, metabolic and cellular programs with a generally beneficial outcome for humans. However, the complexity of multiple, potentially tumor-suppressive pathways at HA impedes the understanding of mechanisms leading to reduced cancer mortality. Many adaptive processes at HA are tightly interconnected and thus it cannot be ruled out that the entirety or at least some of the HA-related alterations act in concert to reduce cancer mortality. In this review we discuss tumor formation as a concept of competition between healthy and cancer cells with improved fitness - and therefore higher competitiveness - of healthy cells at high altitude. We discuss HA-related changes in glucose, lipid and iron metabolism that may have an impact on tumorigenesis. Additionally, we discuss two parameters with a strong impact on tumorigenesis, namely drug metabolism and physical activity, to underpin their potential contribution to HA-dependent reduced cancer mortality. Future studies are needed to unravel why cancer mortality is reduced at HA and how this knowledge might be used to prevent and to treat cancer patients.