Methodological Considerations for Investigating Iron Status and Regulation in Exercise and Sport Science Studies

Running Low: A Seasonal Analysis of Micronutrient Deficiencies on External-Load Measures in Elite Female Rugby League Players

Iron and vitamin D are essential for physiological mechanisms underpinning physical capacities characterizing team-sport performance. Yet, the impact of iron deficiency on physical capacities beyond endurance is not clear.

PURPOSE

The purpose of this study was to assess variations in seasonal micronutrient concentrations and how iron deficiency impacts external-load measures in elite female rugby league players.

METHODS

Iron and vitamin D status were measured in 28 players (age 24 [4] y, body mass 76 [11] kg) across 3 time points of the 17-week National Rugby League Women's season. Physical demands were evaluated using external-load measures (eg, total distance, PlayerLoad) for training and competition. Linear mixed-effects models were employed to assess the effect of change in serum ferritin concentration on external-load measures. Effect sizes with 95% CIs were calculated to interpret the magnitude of difference in change in indices and performance outcomes between iron-deficient and iron-sufficient players.

RESULTS

Iron-deficiency prevalence ranged from 26% to 57% across the season, and <22% of players were vitamin D deficient at each time point. Weak to strong positive associations (R2 = .3-.6) were observed between all external-load measures and moderating variables (serum ferritin, week, position, and athlete). However, these associations were largely attributable to the contribution of week and position. Differences in load measures between iron-deficient and iron-sufficient players were mostly trivial to small.

CONCLUSIONS

Iron status of elite female rugby league players had little effect on most workload measures within this cohort. However, longitudinal monitoring is warranted to identify how external-load measures are affected individually in response to fluctuations in serum ferritin.

Iron deficiency, supplementation, and sports performance in female athletes: A systematic review

BACKGROUND

Iron facilitates key biological functions underpinning sports performance, and up to 60% of female athletes experience iron deficiency. However, the effects of iron deficiency on sports performance in female athletes is unclear, as are the degree of benefits of iron supplementation (FeSup). This study characterizes the effects of iron deficiency and FeSup on sports performance in high-level female athletes.

METHODS

Searches of the electronic databases MEDLINE, SPORTDiscus, Web of Science, Scopus, and CINAHL were performed in July 2023. Studies were included that evaluated the effects of iron deficiency or FeSup on sports performance in high-level (maximal oxygen uptake (VO2max) > 45 mL/kg/min, or trained > 5 h/week) iron deficient (ID) (serum ferritin (sFer) < 40 µg/L) female athletes. Studies were assessed using a modified Downs and Black Quality Assessment Checklist.

RESULTS

A total of 23 studies comprising 669 athletes (age range: 13-47 years) across 16 sports were included in the review. Iron deficiency negatively affects endurance performance by 3%-4%. However, endurance performance improved by 2%-20% when ID athletes were treated with 100 mg/day of elemental iron for up to 56 days via oral supplementation, or bi-daily via parenteral administration over 8-10 days. ID non-anemic athletes with low sFer stores may be predisposed to reduced maximal aerobic capacity. However, maximal aerobic capacity improved by 6%-15% following 16 mg/day-100 mg/day of elemental iron for 36-126 days. Isokinetic strength and anaerobic power performance may be impeded (-23% to +4%) among ID athletes, but the effect of FeSup on anaerobic power varied markedly (-5% to +9%) following 100 mg/day of elemental iron over 42-56 days, or 100 mg of elemental iron bi-daily over 8-10 days. The quality of studies was moderate (77%), ranging from low (57%) to high (100%). Moststudies (n = 18) contained group sizes ≤ 20 athletes, thus limiting the likelihood of detecting significant effects (statistical power > 0.80).

CONCLUSION

High-level ID female athletes experience a negative impact on endurance performance, which can be improved by supplementing with ∼100 mg of elemental iron per day or bi-daily. The decrements in other performance parameters characterizing a range of sports coincide with the severity of iron deficiency.

Iron Absorption in Highly Trained Male Runners: Does it Matter When and Where You Eat Your Iron?

PURPOSE

We examined iron absorption and its regulation during two common scenarios experienced by endurance athletes. Our aims were to: (i) compare the effects of preexercise versus postexercise iron intake on iron absorption; and (ii) compare the impact of training at altitude (1800 m) on iron absorption preexercise.

METHODS

Male runners (n = 18) completed three exercise trials over a 5-wk period, each preceded by 24 h of standardized low-iron diets. First, athletes completed two 60-min treadmill running trials at 65% V̇O2max at near sea-level (580 m). In a randomized order, preexercise and postexercise test meals labeled with 4 mg of 57Fe or 58Fe were consumed 30 min before or 30 min after exercise. Then, the same exercise trial was performed after living and training at altitude (~1800 m) for 7 d, with the labeled test meal consumed 30 min preexercise. We collected venous blood samples preexercise and postexercise for markers of iron status and regulation, and 14 d later to measure erythrocyte isotope incorporation.

RESULTS

No differences in fractional iron absorption were evident when test meals were consumed preexercise (7.3% [4.4, 12.1]) or postexercise (6.2% [3.1, 12.5]) (n = 18; P = 0.058). Iron absorption preexercise was greater at altitude (18.4% [10.6, 32.0]) than at near sea-level (n = 17; P < 0.001) and hepcidin concentrations at altitude were lower at rest and 3 h postexercise compared with near sea level (P < 0.001).

CONCLUSIONS

In an acute setting, preexercise and postexercise iron absorption is comparable if consumed within 30 min of exercise. Preexercise iron absorption increases 2.6-fold at altitude compared with near sea-level, likely due to the homeostatic response to provide iron for enhanced erythropoiesis and maintain iron stores.

Considerations for the Consumption of Vitamin and Mineral Supplements in Athlete Populations

Vitamins and minerals are of fundamental importance to numerous human functions that are essential to optimise athlete performance. Athletes incur a high turnover of key vitamins and minerals and are therefore dependent on sufficient energy intake to replenish nutrient stores. However, many athletes are poor at servicing their energy replenishment needs, especially female athletes, and although a 'food first approach' to meeting nutrient requirements is the primary goal, it may be important for some athletes to consider a vitamin and/or mineral supplement to meet their daily needs. When working to determine if an athlete requires vitamin or mineral supplements, practitioners should use a robust framework to assess the overall energy requirements, current dietary practices and the biological and clinical status of their athletes. Of note, any supplementation plan should account for the various factors that may impact the efficacy of the approach (e.g. athlete sex, the nutrient recommended dietary intake, supplement dose/timing, co-consumption of other foods and any food-drug interactions). Importantly, there are numerous vitamins and minerals of key importance to athletes, each having specific relevance to certain situations (e.g. iron and B vitamins are significant contributors to haematological adaptation, calcium and vitamin D are important to bone health and folate is important in the female athlete); therefore, the appropriate supplement for a given situation should be carefully considered and consumed with the goal to augment an athlete's diet.

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.

Methodology for studying Relative Energy Deficiency in Sport (REDs): a narrative review by a subgroup of the International Olympic Committee (IOC) consensus on REDs

In the past decade, the study of relationships among nutrition, exercise and the effects on health and athletic performance, has substantially increased. The 2014 introduction of Relative Energy Deficiency in Sport (REDs) prompted sports scientists and clinicians to investigate these relationships in more populations and with more outcomes than had been previously pursued in mostly white, adolescent or young adult, female athletes. Much of the existing physiology and concepts, however, are either based on or extrapolated from limited studies, and the comparison of studies is hindered by the lack of standardised protocols. In this review, we have evaluated and outlined current best practice methodologies to study REDs in an attempt to guide future research.This includes an agreement on the definition of key terms, a summary of study designs with appropriate applications, descriptions of best practices for blood collection and assessment and a description of methods used to assess specific REDs sequelae, stratified as either Preferred, Used and Recommended or Potential Researchers can use the compiled information herein when planning studies to more consistently select the proper tools to investigate their domain of interest. Thus, the goal of this review is to standardise REDs research methods to strengthen future studies and improve REDs prevention, diagnosis and care.

Evaluation of Serum Iron Parameters among Men Performing Regular Physical Activity—A Preliminary Study

Iron deficiency anemia is one of the most common issues in clinical practice. It can be caused by intense physical activity, among other things. The aim of the study was to assess serum iron parameters in a group of men who engage in regular physical activity. The study group was composed of 20 men who regularly perform strength or endurance sports, whereas the control group consisted of 20 men without any sports activity. The red blood cell (RBC) parameters, platelet count (PLT), and white blood cell (WBC) count in venous blood samples were assessed with an automated hematology analyzer. The serum concentration of ferritin was determined through an immunology assay. There were no statistically significant differences between groups comparing RBC parameters and WBC. However, statistical analysis showed dissimilarity in PLT count and serum ferritin concentration comparing control and study groups (p < 0.05). It was shown that lower serum ferritin concentration concerns men with regular physical activity, whereas other blood parameters were not affected in this group.