Menstrual phase and ambient temperature do not influence iron regulation in the acute exercise period

Factors Influencing the Hepcidin Response to Exercise: An Individual Participant Data Meta-analysis

BACKGROUND

Hepcidin, the master iron regulatory hormone, has been shown to peak 3-6 h postexercise, and is likely a major contributor to the prevalence of iron deficiency in athletes. Although multiple studies have investigated the hepcidin response to exercise, small sample sizes preclude the generalizability of current research findings.

OBJECTIVE

The aim of this individual participant data meta-analysis was to identify key factors influencing the hepcidin-exercise response.

METHODS

Following a systematic review of the literature, a one-stage meta-analysis with mixed-effects linear regression, using a stepwise approach to select the best-fit model, was employed.

RESULTS

We show that exercise is associated with a 1.5-2.5-fold increase in hepcidin concentrations, with pre-exercise hepcidin concentration accounting for ~ 44% of the variance in 3 h postexercise hepcidin concentration. Although collectively accounting for only a further ~ 3% of the variance, absolute 3 h postexercise hepcidin concentrations appear higher in males with lower cardiorespiratory fitness and higher pre-exercise ferritin levels. On the other hand, a greater magnitude of change between the pre- and 3 h postexercise hepcidin concentration was largely attributable to exercise duration (~ 44% variance) with a much smaller contribution from VO2max, pre-exercise ferritin, sex, and postexercise interleukin-6 (~ 6% combined). Although females tended to have a lower absolute 3 h postexercise hepcidin concentration [1.4 nmol·L-1, (95% CI [- 2.6, - 0.3]), p = 0.02] and 30% less change (95% CI [-54.4, - 5.1]), p = 0.02) than males, with different explanatory variables being significant between sexes, sample size discrepancies and individual study design biases preclude definitive conclusions.

CONCLUSION

Our analysis reveals the complex interplay of characteristics of both athlete and exercise session in the hepcidin response to exercise and highlights the need for further investigation into unaccounted-for mediating factors.

The effects of menstrual cycle phases on immune function and inflammation at rest and after acute exercise: A systematic review and meta-analysis

The immune system plays an important role in mediating exercise responses and adaptations. However, whether fluctuating hormone concentrations across the menstrual cycle may impact these processes remains unknown. The aim of this systematic review with meta-analysis was to compare baseline concentrations as well as exercise-induced changes in immune and inflammatory parameters between menstrual cycle phases. A systematic literature search was conducted according to the PRISMA guidelines using Pubmed/MEDLINE, ISI Web of Science, and SPORTDiscus. Of the 159 studies included in the qualitative synthesis, 110 studies were used for meta-analysis. Due to the designs of the included studies, only the follicular and luteal phase could be compared. The estimated standardized mean differences based on the random-effects model revealed higher numbers of leukocytes (-0.48 [-0.73; -0.23], p < 0.001), monocytes (-0.73 [-1.37; -0.10], p = 0.023), granulocytes (-0.85 [-0.1.48; -0.21], p = 0.009), neutrophils (-0.32 [-0.52; -0.12], p = 0.001), and leptin concentrations (-0.37 [-0.5; -0.23], p = 0.003) in the luteal compared to the follicular phase at rest. Other parameters (adaptive immune cells, cytokines, chemokines, and cell adhesion molecules) showed no systematic baseline differences. Seventeen studies investigated the exercise-induced response of these parameters, providing some indications for a higher pro-inflammatory response in the luteal phase. In conclusion, parameters of innate immunity showed cycle-dependent regulation at rest, while little is known on the exercise responses. Due to a large heterogeneity and a lack of cycle phase standardization among the included studies, future research should focus on comparing at least three distinct hormonal profiles to derive more specific recommendations for exercise prescription.

Serum iron availability, but not iron stores, is lower in naturally menstruating than in oral contraceptive athletes

This study measured serum markers of iron status in naturally menstruating and oral contraceptive (OC) athletes during the main hormonal milieus of these two profiles to identify potential differences confounding the diagnosis of iron deficiency in female athletes. Resting blood samples were collected from 36 naturally menstruating athletes during the early-follicular phase (EFP), mid- late-follicular phase (MLFP) and mid-luteal phase (MLP) of the menstrual cycle. Simultaneously, blood samples were collected from 24 OC athletes during the withdrawal and active-pill phase of the OC cycle. Serum iron, ferritin, transferrin, transferrin saturation (TSAT), C-reactive protein (CRP), interleukin-6 and sex hormones were analyzed. Naturally menstruating athletes showed lower levels of TSAT, iron and transferrin than OC athletes when comparing the bleeding phase of both profiles (p<0.05) as well as when comparing all analyzed phases of the menstrual cycle to the active pill phase of the OC cycle (p<0.05). Interestingly, only lower transferrin was found during MLFP and MLP compared to the withdrawal phase of the OC cycle (p>0.05), with all other iron markers showing no differences (p>0.05). Intracycle variations were also found within both types of cycle, presenting reduced TSAT and iron during menstrual bleeding phases (p<0.05). In conclusion, in OC athletes, serum iron availability, but not serum ferritin, seems higher than in naturally menstruating ones. However, such differences are lost when comparing the MLFP and MLP of the menstrual cycle with the withdrawal phase of the OC cycle. This should be considered in the assessment of iron status in female athletes.Highlights Naturally menstruating athletes present lower TSAT, iron and transferrin in all analyzed phases of the menstrual cycle compared to OC athletes during their active pill phase. However, both the mid-late follicular and mid-luteal phases of the menstrual cycle do not differ from the withdrawal phase of the oral contraceptive cycle.Intracycle variations are found for TSAT and iron in both naturally menstruating and oral contraceptive athletes, which are mainly driven by a reduction in TSAT and iron during menstrual bleeding phases.As serum iron availability changes significantly as a function of the athlete's hormonal status, it should be considered in the assessment of the athlete's iron status as well as standardise the phase of the menstrual cycle in which to assess iron markers to avoid misdiagnosis or misleading results.In contrast, the assessment of iron stores through serum ferritin is substantially stable and the athlete's hormonal status does not seem to be of relevance for this purpose.

Effect of wearing medical protective masks on treadmill running performance in the postpandemic era: a randomised trial

BACKGROUND

In the postpandemic era, wearing protective masks in public places will still be an important means of blocking popular viruses in the future. The purpose of this study was to explore whether sports performance was affected by mask wearing and exercise duration during 15-min treadmill running at a speed of 75% maximal aerobic speed.

METHODS

Thirty-six males were randomly divided into mask and nonmask groups. The kinematic and kinetic data were obtained at four time points (RN_0-1 min, RN_5-6 min, RN_9-10 min, and RN_14-15 min) during running. Two-way mixed ANOVA was applied to examine the effects between groups and times with Bonferroni post hoc comparison and independent samples t-test.

RESULTS

The results showed that there was no difference between mask and nonmask group during running (p > 0.05). As running time increased, hip joint ROM, hip joint flexion/extension max, and ankle joint plantarflexion max angles increased; knee joint flexion min and ankle joint dorsiflexion max angles decreased; average peak vertical ground reaction forces (PVGRF) increased after 9 min-running (p < 0.05).

CONCLUSIONS

Wearing a medical protective mask does not affect the joint angle and touchdown PVGRF of lower extremities during treadmill running while affected by running time and changed after 9 min-treadmill running. Future studies will examine the effects of wearing masks during the pandemic on muscle activation and blood biochemical values during exercise.

TRIAL REGISTRATION NO

ChiCTR2000040535 (date of registration on December 1, 2020). Prospectively registered in the Chinese Clinical Trial Registry.

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.

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.

Do E2 and P4 contribute to the explained variance in core temperature response for trained women during exertional heat stress when metabolic rates are very high?

Purpose

Women remain underrepresented in the exercise thermoregulation literature despite their participation in leisure-time and occupational physical activity in heat-stressful environments continuing to increase. Here, we determined the relative contribution of the primary ovarian hormones (estrogen [E₂] and progesterone [P₄]) alongside other morphological (e.g., body mass), physiological (e.g., sweat rates), functional (e.g., aerobic fitness) and environmental (e.g., vapor pressure) factors in explaining the individual variation in core temperature responses for trained women working at very high metabolic rates, specifically peak core temperature (T_peak) and work output (mean power output).

Methods

Thirty-six trained women (32 ± 9 year, 53 ± 9 ml·kg⁻¹·min⁻¹), distinguished by intra-participant (early follicular and mid-luteal phases) or inter-participant (ovulatory vs. anovulatory vs. oral contraceptive pill user) differences in their endogenous E₂ and P₄ concentrations, completed a self-paced 30-min cycling work trial in warm–dry (2.2 ± 0.2 kPa, 34.1 ± 0.2 °C, 41.4 ± 3.4% RH) and/or warm–humid (3.4 ± 0.1 kPa, 30.2 ± 1.2 °C, 79.8 ± 3.7% RH) conditions that yielded 115 separate trials. Stepwise linear regression was used to explain the variance of the dependent variables.

Results

Models were able to account for 60% of the variance in T_peak (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{R }$$\end{document}R¯²: 41% core temperature at the start of work trial, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{R }$$\end{document}R¯²: 15% power output, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{R }$$\end{document}R¯²: 4% [E₂]) and 44% of the variance in mean power output (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{R }$$\end{document}R¯²: 35% peak aerobic power, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{R }$$\end{document}R¯²: 9% perceived exertion).

Conclusion

E₂ contributes a small amount toward the core temperature response in trained women, whereby starting core temperature and peak aerobic power explain the greatest variance in T_peak and work output, respectively.

Heat acclimation does not attenuate hepcidin elevation after a single session of endurance exercise under hot condition

Purpose

We sought to determine the effects of heat acclimation on endurance exercise-induced hepcidin elevation under hot conditions.

Methods

Fifteen healthy men were divided into two groups: endurance training under hot conditions (HOT, 35 °C, n = 8) and endurance training under cool conditions (CON, 18 °C, n = 7). All subjects completed 10 days of endurance training (8 sessions in total), consisting of 60 min of continuous exercise at 50% of maximal oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2\max }$$\end{document}V˙O2max) under their assigned environment condition. Subjects completed a heat stress exercise test (HST, 60 min exercise at 60% \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2\max }$$\end{document}V˙O2max) to evaluate the exercise-induced thermoregulatory and hepcidin responses under hot conditions (35 °C) before (pre-HST) and after (post-HST) the training period.

Results

Core temperature during exercise in the post-HST decreased significantly in the HOT group compared to pre-HST (P = 0.004), but not in the CON group. The HOT and CON groups showed augmented exercise-induced plasma interleukin-6 (IL-6) elevation in the pre-HST (P = 0.002). Both groups had significantly attenuated increases in exercise-induced IL-6 in the post-HST; however, the reduction of exercise-induced IL-6 elevation was not different significantly between both groups. Serum hepcidin concentrations increased significantly in the pre-HST and post-HST in both groups (P = 0.001), no significant difference was observed between both groups during each test or over the study period.

Conclusion

10 days of endurance training period under hot conditions improved thermoregulation, whereas exercise-induced hepcidin elevation under hot conditions was not attenuated following the training.

Measurement error of self-paced exercise performance in athletic women is not affected by ovulatory status or ambient environment

Measurement error(s) of exercise tests for women are severely lacking in the literature. The purpose of this investigation was to 1) determine whether ovulatory status or ambient environment were moderating variables when completing a 30-min self-paced work trial and 2) provide test-retest norms specific to athletic women. A retrospective analysis of three heat stress studies was completed using 33 female participants (31 ± 9 yr, 54 ± 10 mL·min^-1·kg^-1) that yielded 130 separate trials. Participants were classified as ovulatory (n = 19), anovulatory (n = 4), and oral contraceptive pill users (n = 10). Participants completed trials ∼2 wk apart in their (quasi-) early follicular and midluteal phases in two of moderate (1.3 ± 0.1 kPa, 20.5 ± 0.5°C, 18 trials), warm-dry (2.2 ± 0.2 kPa, 34.1 ± 0.2°C, 46 trials), or warm-humid (3.4 ± 0.1 kPa, 30.2 ± 1.1°C, 66 trials) environments. We quantified reliability using limits of agreement, intraclass correlation coefficient (ICC), standard error of measurement (SEM), and coefficient of variation (CV). Test-retest reliability was high, clinically valid (ICC = 0.90, P < 0.01), and acceptable with a mean CV of 4.7%, SEM of 3.8 kJ (2.1 W), and reliable bias of -2.1 kJ (-1.2 W). The various ovulatory status and contrasting ambient conditions had no appreciable effect on reliability. These results indicate that athletic women can perform 30-min self-paced work trials ∼2 wk apart with an acceptable and low variability irrespective of their hormonal status or heat-stressful environments.NEW & NOTEWORTHY This study highlights that aerobically trained women perform 30-min self-paced work trials ∼2 wk apart with acceptably low variability and their hormonal/ovulatory status and the introduction of greater ambient heat and humidity do not moderate this measurement error.

Sex differences in the physiological responses to exercise-induced dehydration: consequences and mechanisms

Physiological strain during exercise is increased by mild dehydration (∼1%-3% body mass loss). This response may be sex-dependent, but there are no direct comparative data in this regard. This review aimed to develop a framework for future research by exploring the potential impact of sex on thermoregulatory and cardiac strain associated with exercise-induced dehydration. Sex-based comparisons were achieved by comparing trends from studies that implemented similar experimental protocols but recruited males and females separately. This revealed a higher core temperature (T_c) in response to exercise-induced dehydration in both sexes; however, it seemingly occurred at a lower percent body mass loss in females. Although less clear, similar trends existed for cardiac strain. The average female may have a lower body water volume per body mass compared with males, and therefore the same percent body mass loss between the sexes may represent a larger portion of total body water in females potentially posing a greater physiological strain. In addition, the rate at which T_c increases at exercise onset might be faster in females and induce a greater thermoregulatory challenge earlier into exercise. The T_c response at exercise onset is associated with lower sweating rates in females, which is commonly attributed to sex differences in metabolic heat production. However, a reduced sweat gland sensitivity to stimuli, lower fluid output per sweat gland, and sex hormones promoting fluid retention in females may also contribute. In conclusion, the limited evidence suggests that sex-based differences exist in thermoregulatory and cardiac strain associated with exercise-induced dehydration, and this warrants future investigations.