Echinacea-Based Dietary Supplement Does Not Increase Maximal Aerobic Capacity in Endurance-Trained Men and Women

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.

Interleukin-13 drives metabolic conditioning of muscle to endurance exercise

Repeated bouts of exercise condition muscle mitochondria to meet increased energy demand-an adaptive response associated with improved metabolic fitness. We found that the type 2 cytokine interleukin-13 (IL-13) is induced in exercising muscle, where it orchestrates metabolic reprogramming that preserves glycogen in favor of fatty acid oxidation and mitochondrial respiration. Exercise training-mediated mitochondrial biogenesis, running endurance, and beneficial glycemic effects were lost in Il13^-/- mice. By contrast, enhanced muscle IL-13 signaling was sufficient to increase running distance, glucose tolerance, and mitochondrial activity similar to the effects of exercise training. In muscle, IL-13 acts through both its receptor IL-13Rα1 and the transcription factor Stat3. The genetic ablation of either of these downstream effectors reduced running capacity in mice. Thus, coordinated immunological and physiological responses mediate exercise-elicited metabolic adaptations that maximize muscle fuel economy.

Six weeks of oral Echinacea purpurea supplementation does not enhance the production of serum erythropoietin or erythropoietic status in recreationally active males with above-average aerobic fitness

The purpose of this study was to investigate the effect of 6 weeks of oral Echinacea purpurea supplementation on serum erythropoietin (EPO) and erythropoietic status. Twenty-four males (mean ± SE; age = 25.2 ± 1.4 years, height = 178.1 ± 1.4 cm, body mass = 78.1 ± 1.6 kg, body fat = 12.7 ± 0.9%, maximal oxygen uptake = 52.9 ± 0.9 mL·kg^-1·min^-1) were randomly grouped using a matched-pair, double-blind design and self-administered 8000 mg·day^-1 of either E. purpurea (n = 12) or placebo (n = 12) for 42 consecutive days. Blood samples were collected prior to supplementation (day 0) and every 2 weeks during the supplementation period (days 14, 28, and 42) and were analyzed for EPO, red blood cell count, hemoglobin concentration, hematocrit, mean corpuscular volume, and mean corpuscular hemoglobin concentration. Separate 2 × 4 (group × time) factorial ANOVA with repeated measures on time were used to determine statistical differences with significance set at p ≤ 0.05. There were no significant interaction, group, or time effects observed for EPO or erythropoietic status markers for any of the measurement points (p ≤ 0.05). The present study indicated that 6 weeks of oral E. purpurea supplementation in recreationally active males with above average aerobic fitness did not enhance EPO or erythropoietic status. These findings are in contrast with previous reports of E. purpurea supplementation in untrained participants with average fitness levels, but consistent with observations in trained endurance athletes.

Echinacea Supplementation: Does it Really Improve Aerobic Fitness?

PURPOSE

Echinacea is an herbal supplement used by endurance athletes for its performance boosting properties. It is thought that Echinacea improves the blood's oxygen carrying capacity by increasing production of erythropoietin (EPO), a glycoprotein that regulates red blood cell formation. Subsequently, these changes would lead to an overall improvement in maximal oxygen uptake (VO2max) and running economy (RE), two markers of aerobic fitness. The purpose of this review is to briefly discuss the physiological variables associated with distance running performance and how these variables are influenced by Echinacea supplementation.

METHODS

To determine Echinacea's ergogenic potential, human studies that used Echinacea in conjunction to analyzing the blood's oxygen carrying capacity and/or aerobic fitness were assessed.

RESULTS

Taken together, the majority of the published literature does not support the claim that Echinacea is a beneficial ergogenic aid. With the exception of one study, several independent groups have reported Echinacea supplementation does not increase EPO production, blood markers of oxygen transport, VO2max or RE in healthy untrained or trained subjects.

CONCLUSION

To date, the published literature does not support the use of Echinacea as an ergogenic aid to improve aerobic fitness in healthy untrained or trained subjects.