Elevated Serum Hepcidin Levels during an Intensified Training Period in Well-Trained Female Long-Distance Runners

Prevalence of anemia and iron deficiency and its association with body mass index in elite Japanese high school long-distance runners

OBJECTIVES

Anemia is a common condition in long-distance runners (LDRs). Recently, not only iron deficiency (ID) but also energy deficiency has been considered as a risk factor for anemia in athletes but no evidence has yet been established. The aim of this study was to investigate the prevalence of anemia and ID and the influence of body mass index (BMI) on anemia in high-school LDRs.

METHODS

The participants were 406 male and 235 female elite Japanese LDRs who competed in the All-Japan High-School Ekiden Championship 2019. They submitted their anthropometric data and results of a blood test within five days after the competition. The prevalence of anemia and ID and the influence of BMI on anemia were assessed retrospectively.

RESULTS

Mean hemoglobin concentrations (Hb) were 14.8 ± 0.9 g/dl in males and 13.2 ± 0.9 g/dl in females. The prevalence of anemia (Hb < 14 g/dl in males and < 12 g/dl in females) was significantly higher in males (16.3%) than females (6.4%), but males also showed higher prevalence of non-iron deficiency anemia (NIDA) than females (11.6% and 3.0%, respectively). No significant gender difference was found in the prevalence of iron deficiency anemia (IDA) (4.7% in males and 3.4% in females). ID (serum ferritin level < 25 ng/ml) was significantly more prevalent in females (37.4%) than males (18.5%). A binary logistic regression analysis revealed that low BMI was a contributor to anemia in females (odds ratios: 0.577 (95% CI: 0.369-0.901), p = 0.012).

CONCLUSION

In Japanese high-school LDRs, one in six males was anemic, but most males did not have ID. Conversely, one-third of females were diagnosed with ID. Lower BMI was identified as a risk for anemia in females, suggesting that leanness may also lead to anemia in females.

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.

Menstrual cycle affects iron homeostasis and hepcidin following interval running exercise in endurance-trained women

Purpose

Menstrual cycle phase affects resting hepcidin levels, but such effects on the hepcidin response to exercise are still unclear. Thus, we investigated the hepcidin response to running during three different menstrual cycle phases.

Methods

Twenty-one endurance-trained eumenorrheic women performed three identical interval running protocols during the early-follicular phase (EFP), late-follicular phase (LFP), and mid-luteal phase (MLP). The protocol consisted of 8 × 3 min bouts at 85% of the maximal aerobic speed, with 90-s recovery. Blood samples were collected pre-exercise and at 0 h, 3 h and 24 h post-exercise.

Results

Data presented as mean ± SD. Ferritin were lower in the EFP than the LFP (34.82 ± 16.44 vs 40.90 ± 23.91 ng/ml, p = 0.003), while iron and transferrin saturation were lower during the EFP (58.04 ± 19.70 µg/dl, 14.71 ± 5.47%) compared to the LFP (88.67 ± 36.38 µg/dl, 22.22 ± 9.54%; p < 0.001) and the MLP (80.20 ± 42.05 µg/dl, 19.87 ± 10.37%; p = 0.024 and p = 0.045, respectively). Hepcidin was not affected by menstrual cycle (p = 0.052) or menstrual cycle*time interaction (p = 0.075). However, when comparing hepcidin at 3 h post-exercise, a moderate and meaningful effect size showed that hepcidin was higher in the LFP compared to the EFP (3.01 ± 4.16 vs 1.26 ± 1.25 nMol/l; d = 0.57, CI = 0.07–1.08). No effect of time on hepcidin during the EFP was found either (p = 0.426).

Conclusion

The decrease in iron, ferritin and TSAT levels during the EFP may mislead the determination of iron status in eumenorrheic athletes. However, although the hepcidin response to exercise appears to be reduced in the EFP, it shows no clear differences between the phases of the menstrual cycle (clinicaltrials.gov: NCT04458662).

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-022-05048-5.

Heat-Killed Lactococcus lactis subsp. cremoris H61 Altered the Iron Status of Young Women: A Randomized, Double-Blinded, Placebo-Controlled, Parallel-Group Comparative Study

Women are prone to iron deficiency because of increased iron excretion associated with menstruation. This is often treated by oral iron supplementation, although this treatment can cause side effects, such as stomach pain and nausea, with low absorption of ingested iron. Previously, a significant increase in serum iron was observed in association with the consumption of foods containing Lactococcus lactis subsp. cremoris H61 (H61). However, the causal relationship between H61 ingestion and elevated serum iron is still unclear. Therefore, in this study, we aimed to determine the effects of H61 ingestion on the iron status of young women. Healthy young Japanese women (18–25 years of age) ingested either heat-killed H61 or placebo for 4 weeks. Serum iron, transferrin saturation, and ferritin were significantly elevated in the H61 group but remained unchanged in the placebo group. Compared to before the intervention, iron intake remained unchanged during the intervention period, so the change in the iron status of the H61 group was not due to increased iron intake. These results suggest that heat-killed H61 may elevate iron status by enhancing iron absorption.

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.

Iron Metabolism following Twice a Day Endurance Exercise in Female Long-Distance Runners

Iron deficiency anemia (IDA) and iron deficiency (ID) are frequently observed among endurance athletes. The iron regulatory hormone hepcidin may be involved in IDA and/or ID. Endurance athletes incorporate multiple training sessions, but the influence of repeated bouts of endurance exercise within the same day on iron metabolism remains unclear. Therefore, the purpose of the present study was to investigate the influence of twice a day endurance exercise on iron metabolism, including the hepcidin level, in female long-distance runners. Thirteen female long-distance runners participated in this study. They completed the twice-a-day endurance exercise in the morning and afternoon. Blood samples were collected four times in total: at 06:00 (P0), 14:00 (P8), 20:00 (P14), and 06:00 the next day (P24). In addition to the blood variables, nutritional intake was assessed throughout the exercise day. Serum hepcidin levels were significantly elevated (compared to P0) until the following morning (P24). Moreover, dietary analysis revealed that subjects consumed a low volume of carbohydrates (<6 g/kg body mass/day). In conclusion, twice a day endurance exercise resulted in significant elevation of serum hepcidin level 24 h after completion of the exercise in female long-distance runners. Therefore, athletes with a high risk of anemia should pay attention to training frequency and nutritional intake in order to maintain optimal iron metabolism.

Iron Status and Homeostasis Across 2 Competitive Seasons in NCAA Division I Collegiate Cross-Country Runners Residing at Low Altitude

Purpose: Inflammatory cytokines including interleukin-6 can upregulate hepcidin and decrease iron absorption. Endurance exercise is associated with transient increases in cytokines, which may alter the risk of iron deficiency (ID). This study examined whether chronic elevations in basal levels of cytokines and hepcidin were associated with ID in highly trained runners. Methods: Fifty-four collegiate runners (26 males and 28 females) living at ∼1625 m were recruited from an NCAA Division I cross-country team for this prospective cohort study. Over 2 seasons, fasted, preexercise blood draws were performed in the morning 4 times per season and were analyzed for hemoglobin concentration, ferritin, soluble transferrin receptor (sTfR), hepcidin, and 10 cytokines. Stages of ID were defined using ferritin, sTfR, and hemoglobin concentration. During the study, a registered dietician provided all runners with iron supplements using athletic department–created guidelines. Results: Fifty-seven percent of females and 35% of males exhibited stage 2 ID (ferritin <20 ng/mL or sTfR >29.5 nmol/L) at least once. Cytokines, ferritin, and sTfR exhibited changes through the 2 years, but changes in cytokines were not associated with alterations in hepcidin, ferritin, or sTfR. In males and females, lower ferritin was associated with lower hepcidin (both P < .0001). One female exhibited higher hepcidin and lower iron stores compared with other individuals, suggesting a different etiology of ID. Conclusion: ID is common in highly trained collegiate runners. In general, the high prevalence of ID in this population is not associated with alterations in basal hepcidin or cytokine levels.

The Hepcidin-25/Ferritin Ratio Is Increased in University Rugby Players with Lower Fat Mass

Hepcidin-25 is suggested as a surrogate iron status marker in athletes who show exercise-induced anemia; however, the implications of hepcidin concentration in this population remain poorly understood. This study aimed to investigate the relationship between hepcidin and body fat levels in rugby football players. We included 40 male university rugby football players (RUG) and 40 non-athlete controls. All participants underwent an anthropometric analysis and blood testing that included both hepcidin-25 and ferritin levels. The hepcidin-25 level was slightly (11.6%, p = 0.50) higher, and the ferritin level was significantly (35.9%, p < 0.05) lower, in the RUG group than in controls. The hepcidin-25 to-ferritin ratio was significantly higher (62.5%, p < 0.05) in the RUG group. While significant U-shaped correlations were observed between the body fat and ferritin levels in both groups, the correlations between the hepcidin levels and fat mass index were significantly higher in the RUG group (RUG: r = 0.79, controls: r = 0.45). Notably, the RUG with the lower fat mass index group had a higher hepcidin-25 level, lower ferritin level, and then significantly higher hepcidin-25/ferritin ratio. The hepcidin-25/ferritin ratio may serve as a biomarker for iron status in RUG, especially RUG with lower fat mass.

Possible Association of Energy Availability with Transferrin Saturation and Serum Iron during Summer Camp in Male Collegiate Rugby Players

Low energy availability (LEA) may persist in rugby players. However, timely assessment of energy balance is important but is difficult. Therefore, a practical index that reflects energy availability (EA) is essential. A total of 19 male college rugby players participated in a 2-week pre-season summer camp. Their blood sample was collected after overnight fast prior to (Pre), in the middle (Middle), and after (Post) the camp. Their physical activity in the first half of the camp was calculated using the additive factor method in the forwards (FW; numbers 1–8) and backs (BK; numbers 9–15). The participants were categorized as tight five (T5; numbers 1–5), back row (BR; numbers 6–8), and BK for analysis. All the participants lost weight during the camp (range: from −5.9% to −0.1%). Energy balance in the first half of the camp was negative. Transferrin saturation (TSAT) and serum iron levels significantly decreased to half, or even less, compared with the Pre levels at week 1 and remained low. The changes in TSAT and serum iron levels exhibited a significant positive correlation with the changes in body weight (R = 0.720; R = 0.627) and with energy intake (R = 0.410; R = 461) in T5. LEA occurs in rugby summer camp but is difficult to assess using weight change. Alternately, TSAT and serum iron levels after overnight fast may be better predictors of LEA.

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.

Comparisons Between Serum Levels of Hepcidin and Leptin in Male College-Level Endurance Runners and Sprinters

Background: Hepcidin-25 is a 25 amino acid hepatokine and a key regulator of iron metabolism related to iron deficiency anemia. Recent studies have suggested that an elevated hepcidin level is correlated with low energy availability. Leptin is an appetite-suppressing adipokine and has been reported to stimulate hepcidin production in animals and cultured cells. While leptin is modulated by exercise, it is known that endurance runners and sprinters practice different types of exercise. This study investigated and compared the relationships between hepcidin and leptin levels, iron status, and body fat to understand better the risk of iron deficiency anemia in endurance runners and sprinters. Methods: Thirty-six male college track and field athletes (15 endurance runners and 21 sprinters) were recruited for this study. Dietary intake, body composition, and blood levels of ferritin, hepcidin-25, leptin, and adiponectin were measured. Correlations between hepcidin levels and ferritin, body fat, leptin, and adiponectin were evaluated using Pearson's correlation coefficient for each group. Results: The endurance runners had lower hepcidin levels and higher leptin and adiponectin levels compared with sprinters. Ferritin was positively correlated with hepcidin-25 levels in both the endurance and sprinter groups. A positive correlation was observed between hepcidin-25 and body fat or leptin levels only in sprinters. Conclusion: This is the first study investigating the relationship between blood levels of hepcidin and leptin in athletes. The positive correlation between hepcidin-25 and leptin was observed in sprinters but not endurance runners.

Cancer Related Anemia: An Integrated Multitarget Approach and Lifestyle Interventions

Cancer is often accompanied by worsening of the patient's iron profile, and the resulting anemia could be a factor that negatively impacts antineoplastic treatment efficacy and patient survival. The first line of therapy is usually based on oral or intravenous iron supplementation; however, many patients remain anemic and do not respond. The key might lie in the pathogenesis of the anemia itself. Cancer-related anemia (CRA) is characterized by a decreased circulating serum iron concentration and transferrin saturation despite ample iron stores, pointing to a more complex problem related to iron homeostatic regulation and additional factors such as chronic inflammatory status. This review explores our current understanding of iron homeostasis in cancer, shedding light on the modulatory role of hepcidin in intestinal iron absorption, iron recycling, mobilization from liver deposits, and inducible regulators by infections and inflammation. The underlying relationship between CRA and systemic low-grade inflammation will be discussed, and an integrated multitarget approach based on nutrition and exercise to improve iron utilization by reducing low-grade inflammation, modulating the immune response, and supporting antioxidant mechanisms will also be proposed. Indeed, a Mediterranean-based diet, nutritional supplements and exercise are suggested as potential individualized strategies and as a complementary approach to conventional CRA therapy.

Menopause Delays the Typical Recovery of Pre-Exercise Hepcidin Levels after High-Intensity Interval Running Exercise in Endurance-Trained Women

Menopause commonly presents the gradual accumulation of iron in the body over the years, which is a risk factor for diseases such as cancer, osteoporosis, or cardiovascular diseases. Running exercise is known to acutely increase hepcidin levels, which reduces iron absorption and recycling. As this fact has not been studied in postmenopausal women, this study investigated the hepcidin response to running exercise in this population. Thirteen endurance-trained postmenopausal women (age: 51.5 ± 3.89 years; height: 161.8 ± 4.9 cm; body mass: 55.9 ± 3.6 kg; body fat: 24.7 ± 4.2%; peak oxygen consumption: 42.4 ± 4.0 mL·min^-1·kg^-1) performed a high-intensity interval running protocol, which consisted of 8 × 3 min bouts at 85% of the maximal aerobic speed with 90-second recovery. Blood samples were collected pre-exercise, 0, 3, and 24 hours post-exercise. As expected, hepcidin exhibited higher values at 3 hours post-exercise (3.69 ± 3.38 nmol/L), but also at 24 hours post-exercise (3.25 ± 3.61 nmol/L), in comparison with pre-exercise (1.77 ± 1.74 nmol/L; p = 0.023 and p = 0.020, respectively) and 0 hour post-exercise (2.05 ± 2.00 nmol/L; p = 0.021 and p = 0.032, respectively) concentrations. These differences were preceded by a significant increment of interleukin-6 at 0 hour post-exercise (3.41 ± 1.60 pg/mL) compared to pre-exercise (1.65 ± 0.48 pg/m, p = 0.003), 3 hours (1.50 ± 0.00 pg/mL, p = 0.002) and 24 hours post-exercise (1.52 ± 0.07 pg/mL, p = 0.001). Hepcidin peaked at 3 hours post-exercise as the literature described for premenopausal women but does not seem to be fully recovered to pre-exercise levels within 24 hours post-exercise, as it would be expected. This suggests a slower recovery of basal hepcidin levels in postmenopausal women, suggesting interesting applications in order to modify iron homeostasis as appropriate, such as the prevention of iron accumulation or proper timing of iron supplementation.

Ferritin readings in young adult, female university student recreational runners

BACKGROUND

Elite female athletes have shown vulnerability to various degrees of iron deficiency. Less is known about recreational fitness exercisers. A study was done to examine plasma ferritin, an assessor of iron status, in young adult, university student fitness runners.

METHODS

The present study examined serum ferritin concentrations, an indicator of iron status, in 39 female university students (age 18-25) who ran for fitness, but ran less than competition runners. Selected subjects all reported themselves as not anemic.

RESULTS

Mean + SD for 3 mile run time was 26.25 + 3.0 min. The mean ferritin reading was low: 12.4 + 12.3 ng/mL (+ SD). Out of the 39 women, 29 had readings that fell below 15 ng/mL, which some consider the cutoff for iron deficiency. In addition, all but 2 subjects had values below 35, which has been proposed as Stage 1 iron deficiency for athletes. Ferritin levels did not correlate with 3 mile run times (Pearson correlation coefficient, P > 0.05). A 1 mo intervention with 3 minerals that included iron (36 mg/day) significantly raised ferritin values when the iron was bisglycinate (p < 0.05), but not when it was ferrous sulfate (p > 0.05).

CONCLUSION

In this study, a degree of iron deficiency was seen in most of a group of female fitness runners (each of whom had self reported as not being anemic).

Attempt to Determine the Cut-Off Value of Serum Ferritin for Iron Deficiency in Male College Student Runners

For the evaluation of iron nutrition status, the measurement of serum ferritin levels is the most convenient and widely used technique for estimating stored iron. However, the cut-off value of serum ferritin for iron deficiency in athletes has not yet established. This study aimed to determine the cut-off value of serum ferritin to define iron deficiency in male college student runners. This study included 37-43 Japanese male college student runners for each month. Anthropometric measurements and blood collection were conducted from March to December 2018. In all months except May, significant negative correlations were observed between serum ferritin and transferrin levels, total iron binding capacity (TIBC), and unsaturated iron binding capacity. Furthermore, a significant association between serum ferritin levels and TIBC was observed by nonlinear regression analysis. The curvature radius and curvature were calculated using the data from 9 mo, and serum ferritin levels with the smallest curvature radius and the highest curvature in each month were identified. The serum ferritin levels were as follows: 35.0 ng/mL in March, 45.0 ng/mL in April, 40.0 ng/mL in June, 35.0 ng/mL in July, 35.0 ng/mL in August, 35.0 ng/mL in September, 35.0 ng/mL in October, 35.0 ng/mL in November, and 40.0 ng/mL in December. The average value was 37.2 ng/mL. In conclusion, the cut-off value of serum ferritin for defining iron deficiency in runners was determined to be 40.0 ng/mL in this study. This value (40.0 ng/mL) may be useful for iron deficiency screening in runners.

Partial sleep deprivation after an acute exercise session does not augment hepcidin levels the following day

The purpose of the present study was to determine the effects of partial sleep deprivation (PSD) after an exercise session in the evening on the endurance exercise-induced hepcidin response the following morning. Ten recreationally trained males participated under two different conditions. Each condition consisted of 2 consecutive days of training (days 1 and 2). On day 1, participants ran for 60 min at 75% of maximal oxygen uptake ( V ˙ O2max ) followed by 100 drop jumps. Sleep duration at night was manipulated, with a normal length of sleep (CON condition, 23:00-07:00 hr) or a shortened length of sleep (PSD condition). On the morning of day 2, the participants ran for 60 min at 65% of V ˙ O2max . Sleep duration was significantly shorter under the PSD condition (141.2 ± 13.3 min) than under the CON condition (469.0 ± 2.3 min, p < .0001). Serum hepcidin, plasma interleukin (IL)-6, serum haptoglobin, iron, and myoglobin levels did not differ significantly between the conditions (p > .05) on the morning (before exercise) of day 2. Additionally, the 3-hr postexercise levels for the hematological variables were not significantly different between the two conditions (p > .05). In conclusion, the present study demonstrated that a single night of PSD after an exercise session in the evening did not affect baseline serum hepcidin level the following morning. Moreover, a 60 min run the following morning increased serum hepcidin and plasma IL-6 levels significantly, but the exercise-induced elevations were not affected by PSD.

Resistance exercise causes greater serum hepcidin elevation than endurance (cycling) exercise

BACKGROUND

Hepcidin is an iron regulating hormone, and exercise-induced hepcidin elevation is suggested to increase the risk of iron deficiency among athletes.

OBJECTIVE

We compared serum hepcidin responses to resistance exercise and endurance (cycling) exercise.

METHODS

Ten males [mean ± standard error: 172 ± 2 cm, body weight: 70 ± 2 kg] performed three trials: a resistance exercise trial (RE), an endurance exercise trial (END), and a rest trial (REST). The RE consisted of 60 min of resistance exercise (3-5 sets × 12 repetitions, 8 exercises) at 65% of one repetition maximum, while 60 min of cycling exercise at 65% of [Formula: see text] was performed in the END. Blood samples were collected before exercise and during a 6-h post-exercise (0h, 1h, 2h, 3h, 6h after exercise).

RESULTS

Both RE and END significantly increased blood lactate levels, with significantly higher in the RE (P < 0.001). Serum iron levels were significantly elevated immediately after exercise (P < 0.001), with no significant difference between RE and END. Both the RE and END significantly increased serum growth hormone (GH), cortisol, and myoglobin levels (P < 0.01). However, exercise-induced elevations of GH and cortisol were significantly greater in the RE (trial × time: P < 0.001). Plasma interleukin-6 (IL-6) levels were significantly elevated after exercise (P = 0.003), with no significant difference between the trials. Plasma hepcidin levels were elevated after exercise (P < 0.001), with significantly greater in the RE (463 ± 125%) than in the END (137 ± 27%, P = 0.03). During the REST, serum hepcidin and plasma IL-6 levels did not change significantly.

CONCLUSION

Resistance exercise caused a greater exercise-induced elevation in hepcidin than did endurance (cycling) exercise. The present findings indicate that caution will be required to avoid iron deficiency even among athletes in strength (power) types of events who are regularly involved in resistance exercise.

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.

The Short Tandem Repeat of the DMT1 Gene as a Molecular Marker of Elite Long-Distance Runners

The DMT1 gene encodes divalent metal transporter 1, a membrane iron transport protein. Divalent metal transporter 1 influences cellular iron availability, which might further affect aerobic exercise capacity. Short tandem repeat (STR) polymorphisms have been used as genetic markers in the literature, yet the STR polymorphisms of the DMT1 gene have not been well studied. In this current study, we explored the polymorphisms of the DMT1 gene in a group of elite long-distance runners and controls, by using the PCR-RFLP (Restriction Fragment Length Polymorphism) and Gene scan technology. We found that the genotype frequency of the homozygous 258 bp STR polymorphism of the DMT1 gene (258 bp/258 bp) was significantly higher in the athlete group than in the controls (χ² = 14.01, p = 0.006) so does the allele frequency of the 258 bp STR polymorphism (χ² = 12.867, p = 0.008). These data suggested that the STR polymorphism of the DMT1 gene might be correlated with aerobic exercise capacity and the 258 bp homozygous (25 bp/258 bp) could be used as a molecular marker for the talent identification of elite long-distance runners.

Reduction of hemoglobin, not iron, inhibited maturation of red blood cells in male rats exposed to high intensity endurance exercises

The existence of sports anemia, induced by strenuous or long-term exercise and characterized by decreases of red blood cells (RBCs), hemoglobin and iron content, remains to be doubtful. To observe the effects of endurance exercise on RBCs and explain the underlying reason, we designed this study by observing RBCs parameters and iron metabolism in 8-weeks training rats and effects of iron supplement or protein supplement on RBCs. Results showed that erythrocyte counts, hematocrit, mean corpuscular volume and hemoglobin content decreased while RBC distribution width increased in exercised rats at later stage during 8 weeks training. But the contents of serum iron and ferritin decreased only at 1-week and 2-week and returned to normal at 4-week and 8-week. Same as iron content, apparent iron absorption rate was declined at early stage but restored to normal level at 8-week, as well as serum adrenaline, cortisol and insulin levels. Instead, the contents of total protein and albumin in serum were decreased at later stage during 8-weeks training. Furthermore, we observed that protein supplement ameliorated RBCs parameters in rats exposed to 8 weeks swimming exercise, but iron supplement had no effects on RBCs, though it obviously increased iron content of serum and the liver. Based on these results, we drew a conclusion that transient changes of iron metabolism, which may be induced by stress hormone changes, was not the reason for RBCs decrease in endurance exercises but hemoglobin reduction, induced by defects in protein supplement, impeded development of RBCs.

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.

Iron Supplementation during Three Consecutive Days of Endurance Training Augmented Hepcidin Levels

Iron supplementation contributes an effort to improving iron status among athletes, but it does not always prevent iron deficiency. In the present study, we explored the effect of three consecutive days of endurance training (twice daily) on the hepcidin-25 (hepcidin) level. The effect of iron supplementation during this period was also determined. Fourteen male endurance athletes were enrolled and randomly assigned to either an iron-treated condition (Fe condition, n = 7) or a placebo condition (Control condition; CON, n = 7). They engaged in two 75-min sessions of treadmill running at 75% of maximal oxygen uptake on three consecutive days (days 1-3). The Fe condition took 12 mg of iron twice daily (24 mg/day), and the CON condition did not. On day 1, both conditions exhibited significant increases in serum hepcidin and plasma interleukin-6 levels after exercise (p < 0.05). In the CON condition, the hepcidin level did not change significantly throughout the training period. However, in the Fe condition, the serum hepcidin level on day 4 was significantly higher than that of the CON condition (p < 0.05). In conclusion, the hepcidin level was significantly elevated following three consecutive days of endurance training when moderate doses of iron were taken.