Polyphenol supplementation boosts aerobic endurance in athletes

Polyphenol supplementation

boosts aerobic endurance in

athletes: systematic review

Gexin Cao

2†

, Jing Zuo

3†

, Baile Wu

and Ying Wu

Department of Exercise Physiology, School of Sports Science, Beijing Sports University, Beijing, China,

Laboratory of Sports Stress and Adaptation of General Administration of Sport, Beijing Sports University,

Beijing, China,

Department of Anatomy Laboratory, School of Sports Science, Beijing Sports University,

Beijing, China

In recent years, an increasing trend has been observed in the consumption of

speciﬁc polyphenols, such as ﬂavonoids and phenolic acids, derived from green

tea, berries, and other similar sources. These compounds are believed to alleviate

oxidative stress and inﬂammation resulting from exercise, potentially enhancing

athletic performance. This systematic review critically examines the role of

polyphenol supplementation in improving aerobic endurance among athletes

and individuals with regular exercise habits. The review involved a thorough

search of major literature databases, including PubMed, Web of Science,

SCOPUS, SPORTDiscus, and Embase, covering re-search up to the year 2023.

Out of 491 initially identiﬁed articles, 11 met the strict inclusion criteria for this

review. These studies speciﬁcally focused on the incorporation of polyphenols or

polyphenol-containing complexes in their experimental design, assessing their

impact on aerobic endurance. The methodology adhered to the Preferred

Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)

guidelines, and the risk of bias was evaluated using the Cochrane bias risk

assessment tool. While this review suggests that polyphenol supplementation

might enhance certain aspects of aerobic endurance and promote fat oxidation, it

is important to interpret these ﬁndings with caution, considering the limited

number of studies available.

Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/,

identiﬁer CRD42023453321.

KEYWORDS

polyphenols, athletic performance, aerobic endurance exercise, oxidative stress,

systematic review

1 Introduction

Prolonged periods of high-intensity endurance training and competition can lead to

exercise-induced fatigue in athletes (Sánchez Díaz et al., 2022), a decline in muscle function

(Jun-Qing, 2018), and the initiation of oxidative stress (Morgan et al., 2019; Sánchez Díaz

et al., 2022). Ultimately, these factors may impact athletic performance and activity levels. In

recent years, professional sports teams and amateur enthusiasts have widely embraced

natural plant extracts and phytochemicals to enhance their athletic performance, speed up

post-exercise recovery, and maintain their overall physical health (Striegel et al., 2005; Kim

et al., 2011; Darvishi et al., 2013; Knapik et al., 2016). Polyphenols represent a crucial

category of natural botanical extracts, and there is mounting evidence to suggest their

signiﬁcant potential in enhancing athletic performance and aiding recovery (Bai et al., 2022;

OPEN ACCESS

EDITED BY

Tarak Driss,

Université Paris Nanterre, France

REVIEWED BY

Bruce Rogers,

University of Central Florida, United States

Nejmeddine Ouerghi,

Tunis El Manar University, Tunisia

*CORRESPONDENCE

Ying Wu,

[email protected]

†

These authors share ﬁrst authorship

RECEIVED 11 January 2024

ACCEPTED 25 March 2024

PUBLISHED 08 April 2024

CITATION

Cao G, Zuo J, Wu B and Wu Y (2024),

Polyphenol supplementation boosts aerobic

endurance in athletes: systematic review.

Front. Physiol. 15:1369174.

doi: 10.3389/fphys.2024.1369174

access article distributed under the terms of the

Creative Commons Attribution License (CC BY).

The use, distribution or reproduction in other

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author(s) and the copyright owner(s) are

credited and that the original publication in this

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comply with these terms.

Frontiers in Physiology frontiersin.org01

TYPE Systematic Review

PUBLISHED 08 April 2024

DOI 10.3389/fphys.2024.1369174

Liu et al., 2022; López-Torres et al., 2022; Sánchez Díaz et al., 2022;

Roberts et al., 2023; Zare et al., 2023).

Polyphenols are micronutrients present in plants and their

derivatives, such as berries, wine, green tea, and chocolate

(Manach et al., 2004). In addition, they serve as secondary

metabolites in plants that are involved in several critical

processes such as growth, pigmentation, pollination, and defense

against pathogens and environmental changes (Duthie et al., 2003).

Due to their multifunctional effects on various physiological

conditions in organisms, including oxidative stress (Ristow,

2014), chronic diseases (Mandel and Youdim, 2004; Lagouge,

2006), and immunity (Somerville et al., 2016), polyphenols have

emerged as a rapidly growing area of research (Manach et al., 2004).

Polyphenols consist of thousands of compounds, mainly identiﬁed

by one or more hydroxy groups attached to one or more benzene

rings. According to the number of phenolic rings and the connecting

structural elements, four primary categories can be discerned, as

indicated by reference (Bowtell and Kelly, 2019): phenolic acids,

lignans, stilbenes, and ﬂavonoids (Manach et al., 2004). The most

common polyphenolic compounds from different categories and

their main food sources are summarized in Table 1.

In recent years, polyphenols have been frequently associated

with sports and exercise due to their antioxidant properties

(Bojarczuk and Dzitkowska-Zabielska, 2022). The ability of

polyphenols to scavenge free radicals is related to their chemical

structure (Bowtell and Kelly, 2019). Phenolic hydroxyl groups can

provide an electron to free radicals, while the aromatic rings in

polyphenols can stabilize the resulting phenoxyl radicals (Bors et al.,

2001). Polyphenols are metal chelators, which means they can

reduce the formation of free radicals catalyzed by metals (Isabelle

et al., 1994). However, their concentrations in the human body are

relatively low, and plasma phenolic compounds appear to be

unlikely to function as effective direct antioxidants within the

body (Bowtell and Kelly, 2019). There is increasing evidence to

suggest that the antioxidant properties of polyphenols are linked

with the improvement of endogenous antioxidant capacity activated

via the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling

pathway (Somerville et al., 2017; Bowtell and Kelly, 2019; Kitaoka,

2021; Bojarczuk and Dzitkowska-Zabielska, 2022). Nrf2 belongs to

the Cap-N-Collar transcription factor family and has a substantial

function in mitochondrial biogenesis. Nrf2 gene variants associated

with endurance performance were also identiﬁed (Stevenson, 2012;

Kitaoka, 2021). Under static/steady-state conditions, Nrf2 is

continuously degraded through the ubiquitin-proteasome

pathway mediated by Kelch-like ECH-associated protein 1

(Keap1) (Kitaoka, 2021). However, under stress conditions,

Nrf2 translocates into the cell nucleus and binds to the

antioxidant response elements (AREs) of target cell-protective

genes. Studies utilizing Nrf2-deﬁcient mice on a C57BL/

6 background suggest the signiﬁcance of Nrf2 for antioxidant

enzymes in skeletal muscle (Corey et al., 2012; Narasimhan et al.,

2013; Tryon et al., 2016

; Ahn et al., 2018; Kitaoka et al., 2019). There

is evidence suggesting that long-term consumption of polyphenols

can increase the endogenous antioxidant system’s capacity through

the Nrf2 signaling pathway and AREs pathway like the way exercise

adaptation enhances the capacity of the endogenous antioxidant

system (Bowtell and Kelly, 2019).

The addition of polyphenols has the potential to augment the

body’s antioxidant capacity. For instance, male amateur runners,

when consuming grape juice at a dose of 10 mL/kg/day for 2 h before

exercising at 80% VO

2max

intensity until fatigue, showed an increase

in total antioxidant capacity (de Lima Tavares Toscano et al., 2020).

Acute supplementation of 900 mg of cocoa ﬂavanols also increased

the total antioxidant capacity in well-trained male cyclists (Decroix

et al., 2017). In addition, endurance exercise can cause oxidative

damage that may restrict the vasodilation capacity of blood vessels

and result in changes to blood rheology ( Tofas et al., 2019). The

ergogenic effects of polyphenols seem to be related to alterations in

vascular function. For instance, previous research has highlighted

the beneﬁcial effects of pre-supplementation with pomegranate juice

on brachial artery blood ﬂow and vascular diameter before testing

(Roelofs et al., 2017). Similarly, in a long-term study lasting 4 weeks,

daily supplementation of a total of 571 mg of green tea extract rich in

epigallocatechin gallate (EGCG) resulted in a certain degree of

increase in VO

2max

, while maximum cardiac output remained

unaffected by EGCG (Roberts et al., 2015). This suggests that the

enhancement in exercise performance could be attributed to an

increase in the blood oxygen difference between arteries and veins.

In the muscles engaged during exercise, there was a signiﬁcant

improvement in oxygen transport efﬁciency, greatly enhancing

muscle perfusion capacity (Bowtell and Kelly, 2019). Nitric oxide

(NO) functions as a cellular messenger both intracellularly and

extracellularly, and recent studies suggest that polyphenols regulate

speciﬁc cellular mechanisms by promoting endothelial NO

synthesis, which in turn leads to vasodilation and increased

blood ﬂow (Maiorana et al., 2003; Webb et al., 2008). For these

noticeable vascular effects, the most plausible mechanism is likely to

either reducing ROS generation or enhance ROS detoxiﬁcation

capability through the antioxidant system. As the reaction

between superoxide and NO diminishes the production of

TABLE 1 Food sources of the different polyphenol categories and compounds.

Polyphenol categories Compounds Food source

Phenolic acids Benzoic Gallic acid–tea

Lignans Enterodiol Seeds, legumes

Stilbenes Resveratrol Grapes

Flavonoids Epicatechin, Catechins Cocoa, Green tea

Quercetin, Gallotannins and more Apples

Mango and more

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peroxynitrite, the reduction in ROS exposure would enhance the

bioavailability of the effective vasodilator NO. Therefore, in certain

sports disciplines, supplementing with polyphenols to improve

endothelial function and vasodilation, hence enhancing

hemodynamics, could potentially improve athletic performance

(Labonté et al., 2013; Bowtell and Kelly, 2019).

Reactive oxygen species (ROS) are generated in skeletal muscles

during both rest and exercise and serve as ubiquitous cellular signals

within the mitochondria of all mammalian cells (Maraldi, 2013;

Kitaoka, 2021). Under normal circumstances, these ROS are

buffered by the cell’s internal antioxidant systems to prevent the

accumulation of oxidative damage. Recently, there has been some

debate regarding exercise-induced oxidative stress, stemming from

the dual role of reactive oxygen species in cellular biology (Powers

et al., 2020). On one hand, excessive levels of ROS are associated with

oxidative stress, leading to cell damage, aging, and various diseases

(Kruk et al., 2019). On the other hand, moderate levels of ROS are

essential for regulating important physiological processes, including

stress responses (such as exercise) that promote synthesis and

metabolic adaptations (Radak et al., 2005; Musci et al., 2019).

The concept of hormesis explains how low to moderate levels of

ROS can promote cellular adaptive responses, improving

functionality (Radak et al., 2005). Hormesis refers to a biphasic

dose-response relationship, where low doses of a potentially harmful

factor (like ROS) stimulate beneﬁcial adaptive responses, enhancing

cell function and survival, while high doses are detrimental. This

concept suggests that exercise-induced ROS production, below a

certain threshold, is necessary for triggering cellular adaptations

leading to performance enhancement, muscle growth, and increased

metabolic efﬁciency (Calabrese and Baldwin, 1999; Mattson, 2008).

Exercise-induced ROS play a key role in muscle adaptation,

promoting mitochondrial biogenesis and antioxidant defenses

(Powers et al., 2010). However, identifying the optimal levels of

ROS that promote health rather than harm remains a challenge.

Current understanding calls for a balanced approach, allowing for a

certain degree of ROS production to stimulate beneﬁcial synthetic

and metabolic pathways, without causing oxidative damage. This

balance is likely highly individualized, inﬂuenced by factors such as

genetics, lifestyle, and the type and intensity of exercise. During

repetitive muscle contractions, ROS are continuously generated in

an intensity-dependent manner by various enzymatic sources, such

as NADPH oxidase (NOX) (Reid, 2016). NOX is currently the only

known enzyme family with the sole function of ROS production

(Maraldi, 2013), and it plays a crucial role in generating superoxide,

one of the key sources of oxidative stress. Polyphenols can reduce the

formation of peroxynitrite by inhibiting NOX (Maraldi, 2013).

Consequently, this enhances endogenous antioxidant capacity

and preserves the bioavailability of nitric oxide (NO) (Zare et al.,

2023). Therefore, the ergogenic effects of polyphenols seem to be

supported by vascular and antioxidative mechanisms.

Due to the beneﬁts and characteristics of polyphenols

mentioned above, research on polyphenols in the ﬁeld of sports

is becoming increasingly popular. Although there is currently a

substantial body of research, most reviews tend to focus on recovery

from exercise-induced muscle damage (EIMD) (Martin-Rincon

et al., 2020; Carey et al., 2021; Huang et al., 2021; Ortega et al.,

2021; Sánchez Díaz et al., 2022) or the effects of speciﬁc types of

polyphenols on exercise (Braakhuis et al., 2020; Corr et al., 2021).

Reviews addressing effects on exercise performance lack

categorization and discussion of effects on different types of

exercise, and effects on endurance or explosive exercise

performance remain unclear (Vafaee et al., 2019; Braakhuis et al.,

2020;

D’Unienville et al., 2021; Bojarczuk and Dzitkowska-

Zabielska, 2022; Sánchez Díaz et al., 2022). The intake of

exogenous polyphenols may upregulate the endogenous

antioxidant defense system, but the effects of different

supplementation methods and dosages require further discussion.

This review summarizes current research on the effects of

polyphenols or polyphenol compounds on endurance exercise

performance and identiﬁes their effects, providing a basis for

their potential application in endurance activities (amateur or

non-amateur).

2 Methods

This systematic review follows the Preferred Reporting Items for

Systematic Reviews and Meta-Analyses 2020 (PRISMA 2020)

guidelines (Page et al., 2021). The study has been assessed and

registered in the International Prospective Register of Systematic

Reviews (PROSPERO) under the registration number

CRD42023453321, as of 30 August 2023.

2.1 Search strategy

The search for relevant studies was conducted in several

databases, including PubMed, Scopus, Web of Science (WOS),

EBSCO-SPORTDiscus, and Embase. The search covered the

period from the inception of the databases to August 2023. The

search strategy employed both subject headings and Boolean

operators, primarily focusing on two main concepts: polyphenols

and exercise performance. As an example, for the PubMed database,

the search equation was as follows: (“Athletic Performance” [Mesh]

OR Athletic Performances OR Performance, Athletic OR

Performances, Athletic OR Sports Performance OR Performance,

Sports OR Performances, Sports OR Sports Performances) AND

(“Polyphenols” [Mesh] or Polyphenol or Provinols).

2.2 Eligibility criteria

The inclusion and exclusion criteria for this systematic review

are well deﬁned according to the PICOS model: Population (P):

healthy athletes and sports enthusiasts Intervention; (I):

Supplementation with polyphenols or polyphenol compounds,

including combinations of several polyphenols, with clear

supplementation doses; Comparison (C): Comparison between

intervention/experimental groups with similar characteristics and

a placebo group; Outcome (O): Studies that include tests of athletic

or sports performance before and after supplementation with

polyphenols or polyphenol compounds, with available test data;

Study (S): Randomized controlled trials with a parallel or crossover

design, published in English. In addition, exclusion criteria were

speciﬁed as follows: (i) Studies with confounding factors other than

polyphenols. (ii) Studies with types of exercise programs that were

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not consistent with the focus of the research. (iii) Supplements

containing non-standardized polyphenol compounds or

supplements with unknown polyphenol content. (iv) Studies with

incomplete or missing subject information, experimental protocols,

or procedures. (v) Studies with no data available for extraction. (vi)

Inaccessible full-text articles by legitimate means. (vii) Studies

conducted in speciﬁc environments not relevant to the research.

2.3 Study selection

The search for relevant published literature was conducted

jointly by two authors in a standardized manner to assess the

eligibility of the literature. Any disagreements that arose during

the screening process were resolved through discussion and

negotiation. During the screening process, all duplicate articles

and non-clinical trial literature were removed. The screening

process included the examination of titles and abstracts of the

literature, including relevant articles that contributed to the

research. Finally, the literature that met the inclusion criteria was

selected for full-text reading and review.

2.4 Data extraction

After applying the eligibility criteria, the following information

was extracted from each included literature: Bibliographic

information (author(s) and year of publication), study design:

(whether the study design was parallel or crossover, information

on blinding of subjects, sample size), population characteristics (age

of participants, gender distribution, height and weight data, if

available), details of polyphenol supplementation: (types of

polyphenol supplements used, dosage of polyphenol supplements,

timing and method of supplementation). (i) Performance measures:

time to complete the trial, time to fatigue during exercise, power

output, distance covered, speed achieved, maximum aerobic velocity

(MAV), Rate of Perceived Exertion (RPE), exercise economy,

training intensity. (ii) Metabolic metrics: maximum oxygen

consumption (VO2max), oxygen consumption (VO2), carbon

dioxide production (VCO2), respiratory rate (RR), heart rate

(HR), energy metabolism parameters such as carbohydrate

oxidation (CHOox) and fat oxidation (FATox), blood glucose

concentration (glucose), blood lactate concentration (lactate),

blood lactate concentration at certain points (B [La]). (iii)

Antioxidant Capacity Metrics: high-density lipoprotein (HDL)

levels, low-density lipoprotein (LDL) levels, total antioxidant

capacity (TAC), aspartate aminotransferase (AST) levels (U/L),

and other relevant markers of antioxidant capacity.

3 Results

3.1 Study selection

A total of 11 trials were included in this systematic review. Of

these 11 trials, seven had male participants and three had mixed-

gender groups. The initial search of Scopus, PubMed, Web of

Science (WOS), SportDiscus, Embase, and Cochrane yielded

491 relevant articles. After removing 104 duplicate articles,

387 remained. After reviewing the titles and abstracts,

300 articles were excluded as they did not meet the inclusion

criteria. A total of 87 studies were reviewed, of which 76 were

subsequently excluded (for reasons outlined in the

ﬂowchart, Figure 1).

3.2 Characteristics of the studies

3.2.1 Method

Of the 11 trials included in this review, ﬁve used a parallel design

and six used a crossover design (Table 2). In the selected trials,

participants were randomly assigned to either the placebo group or

the experimental group. In nine of these trials, both researchers and

participants were unaware of the treatment allocation, in one trial

researchers were aware of the intervention allocation, and in one

trial participants were aware that they were receiving the

intervention.

3.2.2 Participants

A total of 220 participants were included in the study. Of these,

164 were recreational athletes and 56 were professional athletes.

There was only one study with a mixed sample, including female

participants (5 women and eight men), without a gender

comparison analysis. The age range of the studies included in the

review was approximately 18–48 years.

3.2.3 Intervention

As previously mentioned, among the eleven studies, nine

compared the placebo group with the experimental group, while

two studies conducted comparisons before and after intervention.

Polyphenol-rich concentrated substances such as grape seed extract

(GSE) (Nho and Kim, 2022), decaffeinated green tea extract (dGTE)

(Roberts et al., 2015), New Zealand blackcurrant (NZBC) (Cook

et al., 2015; Willems et al., 2015), organic olive fruit water

phytocomplex (OliP) (Roberts et al., 2023), Montmorency cherry

powder (MC) (Morgan et al., 2019), carob pods (Gaamouri et al.,

2019), Haskap berries (Howatson et al., 2022), Vinitrox

™

combination of speciﬁc proﬁle polyphenols from grape and

apple) (Deley et al., 2017), Cardiose

(Martinez-Noguera et al.,

2019), grape juice (de Lima Tavares Toscano et al., 2020). These

eleven trials used speciﬁc polyphenols and combinations of

polyphenols, and the forms of intake varied, ﬁve trials of

polyphenol supplementation were in capsule form (Cook et al.,

2015; Roberts et al., 2015; Deley et al., 2017; Morgan et al., 2019; Nho

and Kim, 2022), and three trials were in water (Willems et al., 2015;

Gaamouri et al., 2019) or yogurt-soluble form (Howatson et al.,

2022) as the intervention, while other forms of intake included

snacks (de Lima Tavares Toscano et al., 2020) and canned products

(Roberts et al., 2023).

3.3 Results

3.3.1 Sports performance results

Of the eleven studies included in this systematic review, three

measured test completion time (Cook et al., 2015; Morgan et al.,

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2019; Howatson et al., 2022), three assessed exercise to fatigue time

(Deley et al., 2017; de Lima Tavares Toscano et al., 2020; Nho and

Kim, 2022), and three assessed power output-related metrics ( Cook

et al., 2015; Roberts et al., 2015; Martinez-Noguera et al., 2019). One

study reported a speciﬁc metric, τ (time constant) (Roberts et al.,

2023). Three studies measured distance (Roberts et al., 2015;

Gaamouri et al., 2019; de Lima Tavares Toscano et al., 2020).

Two trials assessed speed (Martinez-Noguera et al., 2019;

Howatson et al., 2022). Two studies measured exercise intensity

(Willems et al., 2015; Roberts et al., 2023), two studies provided an

indicator of exercise economy (Cook et al., 2015; Roberts et al.,

2023), and four studies assessed RPE (Roberts et al., 2015; Gaamouri

et al., 2019; Howatson et al., 2022; Roberts et al., 2023). Only one

study used MAV to measure aerobic work capacity ( Gaamouri

et al., 2019).

3.3.2 Metabolic parameters

Of these eleven studies, ten assessed cardiorespiratory function

(Cook et al., 2015; Roberts et al., 2015; Deley et al., 2017; Gaamouri

et al., 2019; Martinez-Noguera et al., 2019; Morgan et al., 2019;

Howatson et al., 2022; Nho and Kim, 2022; Roberts et al., 2023), and

ﬁve assessed energy substances and their oxidation (Cook et al.,

2015; Roberts et al., 2015; Martinez-Noguera et al., 2019; de Lima

Tavares Toscano et al., 2020; Roberts et al., 2023). Five assessed

lactate levels (Cook et al., 2015; Willems et al., 2015; Morgan et al.,

2019; Howatson et al., 2022; Roberts et al., 2023). Only one study

evaluated TOI (Morgan et al., 2019).

3.3.3 Antioxidant parameters

Two of the eleven studies assessed antioxidant parameters, one

assessed CAT, SOD, GSH, GSSG, TBARS (Martinez-Noguera et al.,

2019), and one assessed antioxidant activity, lipid peroxidation (de

Lima Tavares Toscano et al., 2020).

3.4 Risk of bias

The two authors used the Cochrane Collaboration tool from the

Cochrane Handbook for Systematic Reviews of Interventions

(version 5. 1. 0) to assess the risk of bias in the included

FIGURE 1

Selection of studies according to an adapted version of PRISMA 2020 ﬂow diagram.

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TABLE 2 RCT design characteristics for all studies included in this review.

Author Study

design

Characteristics Kind Dose,

timing

Polyphenolic

content

Exercise Physical

performance test

Metabolic

parameters

Anti-

oxidation

parameters

Nho and Kim. (2022)(Nho

and Kim, 2022)

RCT

double-

blind

crossover

I collegiate basketball

players (n = 12) 20. 2 ± 1

GSE 300 mg per day

for 14 days

two bouts of

cycling exercise at

constant

submaximal

workloads

submaximal exercise of

120% of VO

2peak

: time↑

submaximal exercise

of50%, 80%, 120% of

2peak

:HR↔,

VCO

↔,RR↔,Vt↔,

VE↔. RER↔, FMD↑

submaximal exercise

of80%, 120% of

2peak

:VO

↑

Roberts et al. (2015)(Roberts

et al., 2015)

RCT

double-

blind,

parallel

recreationally active males

(n = 14), 21. 4 ± 0. 3

dGTE 571 mg per day

for 4 weeks

400 mg/dEGCG, 91.

21% total catechins

submaximal

assessment and

performance stage

submaximal exercise:

distance covered↑, average

power output↑, RPE↓

submaximal exercise:

↔, VCO

↔, RER↓,

HR↓, SBP↔, DBP↔,

FAT

tot

↑, CHO

tot

↓, TFA

concentration ↔, total

fat acid concentration ↔

Cook et al. (2015)(Cook et al.,

2015)

RCT

double-

blind

crossover

healthy men with a history

of sport participation of

greater than 3 years (n =

14), 38 ± 13

NZBC 300 mg per day

for 7 days

300 mg contains

105 mg anthocyanin

30 min cycling

protocol, 16. 1 km

best effort time-

trial

Submaximal exercise at

45%VO

2max

, 55% VO

2max

65%VO

2max

: power↔,

cycling economy ↔.16.

1 km cycling time-trial:

completion time↓

Submaximal exercise at

45%VO2max, 55%

2max

, 65% VO

2max

↔, VCO

↔,HR↔,

RER↓, Lactose↔,

glucose↔,EE↔,

CHOox↔, FATox↑16.

1 km cycling time-trial:

HR↔, cadence↔

Deley et al. (2017)(Deley et al.,

2017)

RCT

double-

blind,

crossover

healthy physically active

males (n = 48), 31. 0 ± 6. 0

Vinitrox

™

2 capsules of

250 mg

preceding

evening and

1 hour before

the endurance

test

At least 300 mg/day two endurance

tests

endurance test: time to

exhaustion↑, time to reach

maximal perceived

exertion↑

endurance test HR↔,

↔,VE↔,

SBP

max

↔, DBP

max

Gaamouri et al.

(2019)(Gaamouri et al., 2019 )

RCT

double-

blind

parallel

taekwondo athletes (n =

23), 21. 9 ± 1. 2

carob pods 40 g per day for

6 weeks

40 g contains208 mg of

total polyphenol, 14.

4mgofﬂavonoids

yo-yo intermittent

recovery test

level-1

yo-yo intermittent recovery

test: distance↑,

MAV↑, RPE↑

yo-yo intermittent

recovery test: HR↔

Martínez-Noguera et al.

(2019)(Martinez-Noguera

et al., 2019)

RCT

single-

blind

crossover

healthy male amateur

cyclists (n = 15), 33. 3 ± 7.9

Cardiose

500 mg during

and after a

rectangular test

500 mg Rectangular Test.

Repeated Sprints

Test

The best date of Repeated

sprint test: PeakPower↔,

Poweraverage↑, Time to

peakpower↔, Max speed↑,

total energy↑ the average

date of Repeated sprint test:

PeakPower↔,

VT1 VO2↔, VCO2↔,

RER↔,HR↔,

efﬁciency↔,

carbohydrates↔

CAT↔,SOD↔,

GSH↔, GSSG↔,%

GSSG/GSH↔,

TBARS↔

(Continued on following page)

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TABLE 2 (Continued) RCT design characteristics for all studies included in this review.

Author Study

design

Characteristics Kind Dose,

timing

Polyphenolic

content

Exercise Physical

performance test

Metabolic

parameters

Anti-

oxidation

parameters

Poweraverage↔, Time to

peakpower↔Max speed↔,

total energy↔

Willems et al. (2015)(Willems

et al., 2015)

RCT

single-

blind

crossover

trained triathletes

with >3 yrs experience (n =

13) (male = 8, female = 5)

38 ± 8

New Zealand

blackcurrant

6 g per day for

7days

6 g: 138. 6 mg

anthocyanin

Incremental

Cycling Protocols

incremental cycling

1 mmol/L lactate rise:

intensity↑, 4 mmol/L

OBLA: intensity↑

incremental cycling:

DPB↔, SBP↔, MAP↔,

HR↔,SV↔,CO↔,

Plasma lactate↓

de Lima Tavares Toscano et al.

(2020)(de Lima Tavares

Toscano et al., 2020)

RCT

double-

blind,

crossover

recreational male runners

(n = 14), 39 ± 9

grape juice 10 mL/kg/day

for 7 days and

2 h before test

Total phenolics: 3,106.

6/mg/L

Run to exhaustion

test

time to exhaustion↑

distance ↑

fat↔,cho↔ antioxidant activity

↑ lipid peroxidation

response ↔

Howatson et al.

(2022)(Howatson et al., 2022)

RCT

double-

blind

parallel

male recreational runners

(n = 30), 33 ± 7

Haskap berries 6 g per day for

6 days

anthocyanin content

was ~24. 9 mg/g

5 km treadmill

TT, a submaximal

lactate proﬁle

submaximal test: speed↔,

RPE↔5 KM time trail:

mean speed↑, time↓, RPE↔

LT at submaximal test -

HR↓, absolute VO2↑,

relative VO2↓

LTP at submaximal test

HR↓, absolute VO2↔,

relative VO2↔

5 KM time trail:

lactate↔

Roberts et al. (2023)(Roberts

et al., 2023)

RCT

double-

blind

parallel

recreationally active

participants (n = 29) 42 ± 2

OliP 56 mL per day

for 16 days

28 mL contains 315.

9 mg Phenolic Pro ﬁle

Submaximal and

Performance Test

demanding aerobic session:

exercise intensity ↔,

Economy ↔

Aerobic session: VO

↔,

VCO

↔,VE↔, RER↔,

%of baseline VO

2max

↔,

Kcal/d↔, CHO↔,

FAT↔, PRO↔.onset of

submaximal

exercise: VO

↔

Demanding

Aerobic Session

Onset of submaximal

exercise: τ↓

LT1of submaximal

exercise: VO

↓,%

oVO

2max

of baseline↓,

VCO

↔,VE↔, RER↔,

B[La]↔

LT1 of submaximal

exercise: economy↓, RPE↔

LT2 of submaximal

exercise%VO

2max↔

↔, VCO

↔,VE↔,

RER↔, B [La] ↔

LT2 of submaximal

exercise: economy↔, RPE↓

Morgan et al. (2019)(Morgan

et al., 2019)

RCT

double-

trained male cyclists (n =

8), 19. 7 ± 1. 6

MC 462. 8 mg per

day for 7 days

462. 8mg contains

257 mg anthocyanin

10-min steady-

state cycling at ~

15 km time-trial:

completion time ↓

steady stage exercise:

baseline TOI↑, RER↔,

(Continued on following page)

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Cao et al. 10.3389/fphys.2024.1369174

randomized controlled trials (RCTs). The assessment criteria

included: (i) Sequence generation (selection bias). (ii)

Concealment of allocation (selection bias). (iii) Blinding of

participants and staff (performance bias). (iv) Blinding of

outcome assessors (detection bias). (v) Incomplete outcome data

(attrition bias). (vi) Selective reporting (reporting bias). (vii) Other

biases. Each criterion was rated at three levels: low risk, unclear risk,

and high risk, to assess the risk of bias in each study (Figures 2, 3).

3.5 Synthesis of results

3.5.1 Physical performance test

Table 2 shows that three trials assessed exercise time, and all

reported a signiﬁcant reduction in exercise completion time (Cook

et al., 2015; Morgan et al., 2019; Howatson et al., 2022). When

assessing aerobic endurance capacity using the time to fatigue

indicator, three trials showed that the experimental groups had

signiﬁcantly longer fatigue times than the placebo groups (Deley

et al., 2017; de Lima Tavares Toscano et al., 2020; Nho and Kim,

2022). Another time-related measure, time to peak power output,

was measured in two trials, with one showing a signiﬁcant increase

(Deley et al., 2017), and the other showing no signiﬁcant difference

(Martinez-Noguera et al., 2019). Endurance running distance was

assessed in three trials, two of which showed a signiﬁcant positive

effect of the intervention compared to placebo (Roberts et al., 2015;

de Lima Tavares Toscano et al., 2020). In addition, one study showed

a signiﬁcant improvement compared to the pre-supplementation

baseline (Gaamouri et al., 2019). Of the three trials that assessed

power output indicators, one trial showed signiﬁcantly higher results

than the placebo group (Roberts et al., 2015), and one trial showed

no signiﬁcant difference (Cook et al., 2015). In the last of the three

trials, there was no signiﬁcant difference in peak power compared

with the placebo group in the best date and the average date, despite

signiﬁcantly higher mean power in the experimental group of the

best date, not the average date. This study also assessed total energy

produced, with a signiﬁcant increase in total energy produced

during the best date of the repeated sprint compared to the

placebo, although the overall average data during the competition

showed no signiﬁcant difference (Martinez-Noguera et al., 2019).

Two studies assessed exercise intensity, with one study showing no

signiﬁcant difference compared to pre-supplementation (Roberts

et al., 2023), and the other showed a signi ﬁcant improvement

compared with the control group (Willems et al., 2015). In the

two studies that evaluated the economy, one study showed no

signiﬁcant change compared with the placebo group (Cook et al.,

2015). In another study, improvements were observed at the

demanding aerobic session and the ﬁrst lactate turning point

compared with pre-supplementation levels, but there was no

signiﬁcant difference at the second lactate turning point (Roberts

et al., 2023). Four studies used RPE as an effective measure of aerobic

endurance capacity. The result of one paper was a signiﬁcant

decrease in RPE in the polyphenol supplement group compared

to the control group (Roberts et al., 2015). One study showed no

signiﬁcant difference at the ﬁrst lactate turning point compared to

pre-supplementation levels, but a signiﬁcant decrease at the second

lactate turning point (Roberts et al., 2023). Another study also

showed a signiﬁcant increase compared to pre-supplementation

TABLE 2 (Continued) RCT design characteristics for all studies included in this review.

Author Study

design

Characteristics Kind Dose,

timing

Polyphenolic

content

Exercise Physical

performance test

Metabolic

parameters

Anti-

oxidation

parameters

blind

parallel

65% VO2peak,15-

km Time Trial on

two occasions

mean SS exercise TOI

↔, mean VO2↔,

Lactate↑ 15 km time-

trial: RER↔, TOI ↔,

mean VO2↔, Lactate↔

- content not speciﬁed: ↔ no signiﬁcant difference; ↑ signiﬁcantly higher than placebo group; ↓ signiﬁcantly lower than placebo group; abbreviations: RCT, randomised controlled trials; HR, heart rate; RR, respiratory rate; Vt, tidal volume; VE, minute ventilation;

VO2max, maximal oxygen uptake; VO2, volume of oxygen; VCO2, volume of carbon dioxide; RER, respiratory exchange ratio; FMD, ﬂow-mediated dilatation; CHOtot, total carbohydrate oxidation; FATtot, total fat oxidation; EE, energy expenditure; SBP, systolic

blood pressure; DBP, diastolic blood pressure; TFA, total fatty acid; CHOox, carbohydrate oxidation; FATox, fat oxidation; τ, time constant; RPE: rate of perceived exertion; B [La], blood lactate concentration; CHO, carbohydrate; PRO, protein; TOI, tissue oxygenation

index; MAV, maximal aerobic velocity; OBLA, onset of blood plasma lactate accumulation; MAP, mean arterial pressure; SV, stroke volume; CO, cardiac output; TPR, total peripheral resistance; CAT, catalase; SOD, superoxide dismutase; GSH, reduced glutathione;

GSSG, glutathione peroxidase; % GSSG/GSH, % glutathione peroxide/reduced glutathione; TBARS, thiobarbituric acid reactive substances.

Frontiers in Physiology frontiersin.org08

Cao et al. 10.3389/fphys.2024.1369174

(Gaamouri et al., 2019). In the last of these three studies, there was

no signiﬁcant change in RPE during exercise testing compared with

the placebo group (Howatson et al., 2022). Speed is a valuable

indicator of exercise performance. In one study, there was no

signiﬁcant difference in subjects’ speed during submaximal

testing compared to placebo, but there was a signiﬁcant

improvement in the 5K time trial (Howatson et al., 2022). In

another study using this speed indicator, the best performance

for maximal speed was signiﬁcantly improved compared to the

placebo, but the average data for maximal speed showed no

signiﬁcant difference (Martinez-Noguera et al., 2019). One study

used the time constant as an indicator and showed signiﬁcant

differences at the beginning of exercise after the intervention

(Roberts et al., 2023). Only one study assessed MAV and showed

a signiﬁcant improvement compared with pre-supplementation

(Gaamouri et al., 2019). In trials involving female athletes, no sex

differences were analyzed for any of the physical performance

variables (Deley et al., 2017).

3.5.2 Metabolic parameters

When HR was assessed in eight trials, two of them showed a

signiﬁcant decrease compared with the placebo group (Roberts et al.,

2015; Howatson et al., 2022). Of the remaining six trials, one did not

show a signiﬁcant difference compared with pre-supplementation

values (Gaamouri et al., 2019). The results of the other trials showed

no signiﬁcant change compared with the placebo group (Cook et al.,

2015; Willems et al., 2015; Deley et al., 2017; Martinez-Noguera

et al., 2019; Nho and Kim, 2022). In addition, when VO

was

assessed in eight trials, one trial showed a signiﬁcant increase

compared with the placebo group (Nho and Kim, 2022). In the

remaining ﬁve trials, there was no signiﬁcant change in VO

during

the exercise test compared with placebo (Cook et al., 2015; Roberts

et al., 2015; Deley et al., 2017; Martinez-Noguera et al., 2019; Morgan

et al., 2019). In one study, VO

did not show a signiﬁcant difference

compared to pre-supplementation during high-intensity aerobic

exercise, submaximal exercise onset, and the LT2 of submaximal

exercise. However, there was a signiﬁcant decrease in VO

LT1 during submaximal exercise (Roberts et al., 2023). Another

study showed a signiﬁcant increase in absolute VO

at the LT point

of the submaximal test, a signiﬁcant decrease in relative VO

and no

signiﬁcant change at the LTP point of the submaximal test. Relative

has no signiﬁcant difference during the whole exercise

(Howatson et al., 2022). Of the ﬁve trials that evaluated VCO

FIGURE 2

Risk of bias graph: Review of authors’ judgment on each risk of bias item from Cochrane Handbook for Systematic Reviewers (version 5. 1. 0)

presented as percentages across all included studies.

FIGURE 3

Risk of bias summary: Review of authors’ judgment on each risk

of bias item from Cochrane Handbook for Systematic Reviewers

(version 5. 1. 0).

Frontiers in Physiology frontiersin.org09

Cao et al. 10.3389/fphys.2024.1369174

four showed no signiﬁcant difference compared to placebo (Cook

et al., 2015; Roberts et al., 2015; Martinez-Noguera et al., 2019; Nho

and Kim, 2022), and only one trial showed no signiﬁcant change in

VCO

over the entire study period compared to pre-

supplementation (Roberts et al., 2023). When assessing RER

measurements about VO

and VCO

in ﬁve trials, two trials

showed a signiﬁcant decrease compared to the placebo group

(Cook et al., 2015; Roberts et al., 2015), while three trials showed

no signi ﬁcant change compared to the placebo group (Martinez-

Noguera et al., 2019; Morgan et al., 2019; Nho and Kim, 2022). Of

note, one study showed no signiﬁcant difference in RER compared

with pre-supplementation (Roberts et al., 2023). Of the three studies

that evaluated indicators of pulmonary ventilation, two found no

signiﬁcant difference in VE compared with the placebo group (Deley

et al., 2017; Nho and Kim, 2022). One study also found no signi ﬁcant

difference compared to before supplementation, and this study also

assessed VE/VO

and VE/VCO

and found no signiﬁcant

differences (Roberts et al., 2023). Another measure related to

RER was examined in one article, RR, which showed no

signiﬁcant difference compared to the control group (Nho and

Kim, 2022). Three trials evaluated systolic and diastolic blood

pressure as effective measures of aerobic performance and

showed no signiﬁcant differences compared to placebo (Roberts

et al., 2015; Deley et al., 2017). Another study evaluated three

indicators of cardiovascular function, SV, CO, and MAP except

DPB and SBP, but found no signiﬁcant differences compared with

placebo (Willems et al., 2015). Lactate levels were assessed in ﬁve

trials, two of which showed no signiﬁcant difference compared with

placebo (Cook et al., 2015; Howatson et al., 2022), and one showed a

signiﬁcant decrease compared to placebo (Willems et al., 2015).

However, one of these had a unique ﬁnding in that lactate levels

increased signiﬁcantly during the steady-state (SS) phase of exercise,

but showed no signiﬁcant difference during a 15 km time trial

(Morgan et al., 2019). In the latter study, blood lactate

concentrations at both the ﬁrst and second lactate thresholds w

showed no signiﬁcant difference than before supplementation

(Roberts et al., 2023). Another marker related to lactate, blood

glucose, was only assessed in one study and showed no

signiﬁcant difference compared to the placebo group (Cook et al.,

2015). Energy substrates and their oxidative metabolism related to

aerobic endurance performance were also assessed. Four trials

assessed fat and their oxidation, while ﬁve trials assessed

carbohydrates and their oxidation. Of the four trials that

measured fat-related indices, two trials showed a signiﬁcant

increase in fat oxidation compared with the placebo group (Cook

et al., 2015; Roberts et al., 2015), one trial showed no signiﬁcant

change compared with placebo (de Lima Tavares Toscano et al.,

2020), and another trial showed no signiﬁcant difference compared

with before supplementation (Roberts et al., 2023). However, in one

study, despite a signiﬁcant increase in fat oxidation compared with

the placebo group, there was no signiﬁcant difference in TFA

concentration (Roberts et al., 2015

). In another study, fat

oxidation during high-intensity aerobic exercise did not show a

signiﬁcant change compared to pre-supplementation, and similarly,

carbohydrates and proteins did not change signiﬁcantly compared

to pre-supplementation, resulting in no signiﬁcant difference in

heat-generated (Roberts et al., 2023). With regard to carbohydrates,

one study showed a signiﬁcant decrease in carbohydrate oxidation

compared to placebo (Roberts et al., 2015), whereas the other four

studies showed no signiﬁcant differences (Cook et al., 2015;

Martinez-Noguera et al., 2019; de Lima Tavares Toscano et al.,

2020; Roberts et al., 2023). Only one trial evaluated TOIs and one

trial evaluated FMD. However, in this study, baseline TOI was

signiﬁcantly increased compared to placebo, but there was no

signiﬁcant difference during steady-state (SS) exercise or the 15-

km time trial (Morgan et al., 2019). However, there was a signiﬁcant

increase in FMD compared to the control group (Nho and

Kim, 2022).

3.5.3 Antioxidant parameters

Of the 11 trials, only two assessed antioxidant capacity or

antioxidant markers. One study evaluated CAT, SOD, GSH,

TBARS, and % GSSG/GSH, but found no signiﬁcant differences

compared to the placebo group (Martinez-Noguera et al., 2019). In

another study, assessment of antioxidant capacity before and after

supplementation showed a signiﬁcant improvement in antioxidant

activity, but there was no signiﬁcant difference in lipid peroxidation

response. This study also assessed TAC and MDA levels in relation

to antioxidant capacity but found no signiﬁcant differences

compared with placebo (de Lima Tavares Toscano et al., 2020).

4 Discussion

The systematic review of 11 studies in this article demonstrates

notable enhancements in several indicators of aerobic endurance

exercise performance through polyphenol supplementation. These

improvements encompass mean speed, power output, and distance

covered. Notably, the most discernible enhancements were

witnessed in the time taken to complete the exercise test and the

time to fatigue, both of which exhibited substantial improvements

when compared to the placebo group or the pre-supplementation

status. Furthermore, there was a marked increase in fat oxidation.

However, the results from these 11 trials also suggest limited effects

of polyphenol supplements on cardiovascular function, pulmonary

ventilation, gas exchange, and carbohydrate oxidation. Additionally,

one of the two trials assessing antioxidant status demonstrated a

signiﬁcant improvement with polyphenol supplementation (de

Lima Tavares Toscano et al., 2020).

This review is consistent with the ﬁndings of previous literature

that polyphenol supplementation can improve aerobic endurance

performance (Braakhuis and Hopkins, 2015; Somerville et al., 2017).

Previously, there have been some systematic reviews and meta-

analyses of the effects of polyphenols on exercise performance.

However, they have certain limitations: some of the literature

they included did not specify the polyphenol content of the

intervention, and there is currently no review that categorizes the

exercise protocols studied. Different forms of exercise have very

different emphases. Aerobic endurance is crucial for endurance

sports, whereas anaerobic explosive exercise emphasizes

anaerobic explosiveness and strength-related metrics. This review

focuses primarily on the effects of polyphenols on aerobic endurance

performance in endurance sports.

This systematic review encompassed both professional athletes

and sports enthusiasts (non-athletes). The focus among professional

athletes was primarily on endurance sports, including marathon

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Cao et al. 10.3389/fphys.2024.1369174

runners, cyclists, and triathletes. Additionally, athletes from sports

such as basketball and taekwondo, which demand signiﬁcant aerobic

endurance during their activities, were included. Prolonged or high-

intensity exercise can trigger oxidative and inﬂammatory responses

in the body (He et al., 2016; Metsios et al., 2020; Powers et al., 2020).

Sports like marathons, triathlons, and cycling time trials typically

entail extended periods of competition. Conversely, basketball,

characterized by rapid transitions and tactical demands,

necessitates players to sustain prolonged periods of movement on

the court. Thus, aerobic endurance holds particular signiﬁcance in

these sports. However, these prolonged and high-intensity athletic

activities can induce oxidative damage to the body, ultimately

impacting athletic performance. This raises the question of

whether supplementation with polyphenols, a common

exogenous antioxidant, can enhance the aerobic endurance

performance of athletes or amateur sports enthusiasts.

4.1 Beneﬁts and mechanisms of polyphenols

on aerobic performance

Blackcurrants are a fruit rich in polyphenolic compounds that

we use every day. In addition to small amounts of ﬂavanols and

ﬂavonols, they also contain anthocyanins and various glycosides

(Cook et al., 2015). Cyanidin is a type of ﬂavonoid with certain anti-

inﬂammatory (Zhu et al., 2013) and antioxidant (De la Cruz et al.,

2013) properties. Besides blackcurrants, several food sources are rich

in cyanidin, main fruits such as grapes, Montmorency cherries, and

others (Bowtell and Kelly, 2019). Several trials included in this

review used cyanidin-rich polyphenolic compounds as

interventions. These included blackcurrant extract capsules (Cook

et al., 2015; Willems et al., 2015), Montmorency cherry capsules

(Morgan et al., 2019), Haskap berries (Howatson et al., 2022), grape

and apple extract capsules (Deley et al., 2017) and grape juice (de

Lima Tavares Toscano et al., 2020). Previous research consistently

indicates that anthocyanins and polyphenol-rich foods have a

positive impact on oxidative stress, inﬂammation, and muscle

recovery indices (Howatson et al., 2010; Bell et al., 2014; Bell

et al., 2015; Bowtell and Kelly, 2019). However, in previous

reviews or meta-analyses, there has been a relative scarcity of

data or analysis concerning exercise performance (Kimble et al.,

2023). Looking at the combined literature, we ﬁnd that

supplementation with these cyanidin-rich polyphenols has shown

improvements in several exercise performance-related indicators. In

de Lima et al. (de Lima Tavares Toscano et al., 2020), athletes ran for

an average of 59.2 ± 27.8 min and covered an average distance of

12.6 ± 6.3 km after consuming a placebo drink until exhaustion.

However, after ingesting purple grape juice, they exhibited

signiﬁcantly better performance, running on average 9.2 min

longer than the placebo group, representing an 18.7%

improvement, and covering an additional 1.9 km compared to

the placebo group. Similarly, in Nho et al. (Nho and Kim, 2022),

the time to exhaustion during exercise was 128.9 ± 53.0 s in the

placebo group and signiﬁcantly increased to 134.4 ± 58.4 s in the

green tea extract group. Gaelle Deley et al. found a noteworthy

increase in exercise-to-fatigue time (+9.7% ± 6.0%) in the Vinitrox

™

group compared to the placebo group in the endurance test (Deley

et al., 2017). In Morgan et al. (Morgan et al., 2019), a randomized

controlled trial showed that time trial (TT) completion time based

on Montmorency cherries (1,506 ± 86 s) was 4.6% ± 2.9% faster than

that based on the placebo (PL) (1,580 ± 102 s), indicating that

polyphenol supplementation could reduce race completion time.

Additionally, Cook et al. (Cook et al., 2015) found that

supplementing with New Zealand blackcurrant, compared with

the placebo group, reduced the 16.1 km running time from

1722 ± 131 s in the control group to 1,678 ± 108 s in the

supplement group, resulting in a 2.4% performance

improvement. Furthermore, Howatson et al. (Howatson et al.,

2022) found that the Haskap group, supplemented with Haskap

berries, improved their 5 KM time trial performance by

approximately 21 s compared to the placebo group, equivalent to

an increase in average running speed of 0.25 km/h, representing a

performance improvement of more than 2%. In 2015, Roberts et al.

(Roberts et al., 2015) recruited 14 men to participate in a

randomized controlled trial by randomly assigning either a

supplement capsule containing dGTE or a placebo for 4 weeks,

followed by a 40-min performance trial at weeks 0, 2, and 4. The use

of dGTE led to a gradual increase in distance covered, from 20.23 ±

0.54 km in week 0–21.77 ± 0.49 km in week 2, and ﬁnally, to 22.43 ±

0.40 km in week 4, showing a signiﬁcant increase of 10.9%. Similarly,

a signiﬁcant increase in average power output was observed. The

average power output increased by 17.9% from week 0 (162.06 ±

10.08W) to week 2 (191.08 ± 10.85W), and from week 0 to week 4

(198.91 ± 8.61W) increased by 22.7%. This suggests that

supplementation with polyphenols, primarily cyanidin-rich

compounds, beneﬁts both recreational and professional athletes

in terms of aerobic endurance performance, despite variations in

supplement form and dosage. The mechanism behind the

improvement in exercise performance with cyanidin

supplementation is related to the improvement in endothelial

function. The mechanism by which supplementing anthocyanins

improves exercise performance is related to the enhancement of

endothelial function. NO is an efﬁ cient vasodilator capable of

mediating and regulating vascular function and blood ﬂow

during exercise (Ferguson et al., 2013; Lee et al., 2015). By

increasing the production of endothelium-derived vasodilator

NO, supplementation of anthocyanins can mediate endothelium-

dependent vasodilation induced in the thoracic aorta of rats

(Nakamura et al., 2002). Another non-glycosylated anthocyanin

in blackcurrants, delphinidin, can also increase endothelial NO

production to vasodilate blood vessels by elevating intracellular

concentration in endothelial cells. This increase in NO,

along with a reduction in NO free radical breakdown, contributes

to enhanced peripheral blood ﬂow (Martin et al., 2010).

Recruiting 12 elite athletes, Nho et al. (Nho and Kim, 2022)

conducted a study to compare the effects of GSE and placebo on

endothelial function during 14 days of progressive cycling. Brachial

endothelial function was assessed using Flow-Mediated Dilation

(FMD). The results indicated that GSE led to an increase in brachial

artery diameter induced by FMD (14.4% ± 5.2% vs. 17.6% ± 4.5%).

The study demonstrated that long-term supplementation of GSE

improved endurance performance, possibly attributed to the

vasodilation of active skeletal muscle mediated by enhanced

endothelial functio. (Howatson et al., 2022). Haskap berries

containing cyanidin-3-O-glucoside (C3G) have been shown to

increase mitochondrial biogenesis, improve muscle function, and

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Cao et al. 10.3389/fphys.2024.1369174

enhance exercise performance in rodents (Matsukawa et al., 2017;

Saclier et al., 2020). In the literature we examined, a study on Haskap

berries supplementation caught our attention. The research involved

30 male recreational runners in a double-blind, placebo-controlled,

independent group design. The participants were randomly assigned

to either the Haskap berries intervention or an isocaloric placebo

control to investigate the impact of Haskap berries on parameters

related to endurance running performance. The study observed

slight changes in heart rate and VO

2max

at submaximum

intensity. Notably, during the VO

2peak

test, the Haskap group

showed a 20-s extension in exercise-to-fatigue time, representing

a meaningful improvement in the context of human running

performance (Deley et al., 2017). During intense exercise,

upregulation of antioxidant genes and protein expression

mediated by Nrf2 through C3G helps maintain muscle function.

Therefore, Haskap berries may potentially enhance performance by

modulating endothelial function pathways through C3G mediation

(Xu et al., 2004; Edwards et al., 2015). It is therefore speculated that

the improvement in vascular endothelial function leads to increased

utilization at low intensities. This may explain changes in

associated fatigue times and TT race performance. Future

research should reﬁne this concept more systematically and strive

to comprehensively investigate various aspects of the proposed

mechanism to gain a more enriched understanding of the impact

of dietary anthocyanins on exercise performance. Attempting to

elucidate a singular mechanism through simpliﬁed approaches may

not be practical.

4.2 Effects of polyphenols on energy

metabolism during aerobic exercise

In this review, we found that consuming polyphenols may have

an impact on fat metabolism. In Cook et al. (Cook et al., 2015) well-

trained endurance athletes who supplemented with blackcurrant

extract capsules for 1 week showed a signiﬁcant difference in the

outcome measure FATox between the experimental group (0. 44 ± 0.

12) and the placebo group (0. 37 ± 0. 15). This suggests that

supplementation with blackcurrant extract capsules may enhance

whole-body fat oxidation during moderate-intensity exercise. The

appearance of lactate may have been inﬂuenced by the effect of

anthocyanins on substrate oxidation, potentially leading to an

increased contribution of fat oxidation at relatively low intensities

(Willems et al., 2015). Tsuda et al. (Tsuda et al., 2005) in 2005 found

that glycoside-treated adipocytes upregulated genes related to fat

metabolism and signaling. Similarly, Benn et al. (Benn et al., 2014)

found that long-term intake of blackcurrant extract increased energy

metabolism-related genes and mRNA levels in C57BL/6J mice.

Therefore, the increase in fat oxidation may result from the

combined effects of multiple pathways including the upregulation

of genes related to fat oxidation, transportation of fatty acids to

mitochondria, enhanced availability of nitric oxide, and increased

peripheral blood ﬂow. Similar ﬁndings were replicated in another

study involving green tea extract. Roberts et al. (Roberts et al., 2015)

enrolled fourteen recreationally active males and randomly

administered either green tea extract or a placebo. The results

revealed a noteworthy increase in the total fat oxidation rate

within the dGTE group, rising from 0.241 ± 0.025 g/min to

0.301 ± 0.009 g/min, marking a substantial increase of 24.9%.

The beneﬁts of green tea extract on the human body are

primarily associated with the catechin polyphenols, a signiﬁcant

proportion of which is EGCG (Randell et al., 2014), EGCG

upregulates cell signaling not only through antioxidant protective

mechanisms but also via the mediation of PGC1α (Hodgson et al.,

2013), SIRT1 and the mAPK pathway (Vincent et al., 2013; Kim

et al., 2014). Over a longer period (>4 weeks), moderate doses of

EGCG may promote the upregulation of genes associated with fat

metabolism during exercise, thereby enhancing whole-body fat

oxidation. Some studies also suggest that EGCG may improve

glucose tolerance, insulin sensitivity, and adiponectin levels,

further supporting this notion (Potenza et al., 2007; Venables

et al., 2008). In contrast, Martinez et al. (Martinez-Noguera et al.,

2019) in 2019 showed that acute supplementation with hesperidin

increased activation of the intracellular signaling pathway AMPK,

induced changes in PGC1α activity, and promoted the use of fat as

an energy substrate. Increased FATox implies a degree of glycogen

sparing during moderate-intensity exercise. Howatson et al.

(Howatson et al., 2022) found that HR and VO

were lower at a

certain exercise intensity (lactate threshold). As fat oxidation

consumes more oxygen than carbohydrate oxidation, fat may not

be the preferred energy substrate under these circumstances.

Similarly, at moderate intensity (50% VO

2max

), subjects’ FATox

increased from 0. 241 ± 0. 025 to 0. 301 ± 0. 009 g-min-1 after

supplementation with green tea extract, an improvement of

approximately 24. 9%. However, the magnitude of the increase

was more signiﬁcant than in the previous study. The subjects in

this study were recreationally active, so it has been suggested that the

combined effect of exercise training and polyphenol

supplementation may be more appropriate for untrained

individuals (Randell et al., 2014). In the studies considered, grape

seed extract exhibited no signiﬁcant impact on the performance of

primary basketball players (Nho and Kim, 2022). However, among

non-endurance sports athletes, supplementation with carob

demonstrated a signiﬁcant improvement in maximal aerobic

velocity (MAV) and performance in the yoyo test compared to

baseline for professional taekwondo athletes. Gaamouri et al.

(Gaamouri et al., 2019) recruited 23 taekwondo athletes for their

experiment. Prior to the study intervention, there were no signiﬁcant

differences between the groups. After the intervention, the carob

supplement group showed signiﬁcant improvements of 92.43% in

distance and 12.18% in MAV, whereas the placebo group only

exhibited improvements of 40.37% and 4.95%, respectively. This

result indicates that polyphenol supplementation can effectively

enhance the athletic performance of professional athletes.

Carbohydrates and fats are the most important substrates for

energy metabolism during exercise. However, the proportion of

energy contribution from these substrates varies with different

exercise durations and intensities. During low to moderate-

intensity exercise (up to 60% of VO

2max

), the absolute value of

fat oxidation increases (Dandanell et al., 2017). As exercise intensity

further increases, the absolute rate of fat oxidation decreases, and

carbohydrates become the primary energy substrate (Dandanell

et al., 2017). In the process of exercise, the ability to oxidize fats

at a high rate is considered an advantage for endurance-trained

athletes. Muscle glycogen stores are relatively small; therefore,

theoretically, any intervention that enhances skeletal muscle fat

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Cao et al. 10.3389/fphys.2024.1369174

oxidation capacity could lead to glycogen sparing and thereby

enhance endurance (Randell et al., 2014). Endurance exercise

training leads to skeletal muscle adaptations that favor fat

metabolism (Tunstall et al., 2002). Trained individuals exhibit

higher absolute fat oxidation rates compared to untrained

populations (Nordby et al., 2010). However, the increase in fat

oxidation following polyphenol intervention is relatively smaller in

trained individuals compared to untrained ones, explaining the

more signi ﬁcant impact of polyphenols on exercise performance

in untrained individuals or those engaged in non-endurance

activities. In recent years, the topic of olive-derived supplements

has gained popularity. In Roberts et al. (Roberts et al., 2023)in 2023,

an olive-derived supplement rich in hydroxytyrosol, an important

polyphenol, may support endogenous antioxidant mechanisms

related to mitochondrial respiratory capacity, such as

upregulation of PGC-1α (Feng et al., 2011; Wood Dos Santos

et al., 2018), This study showed no difference in VO

2max

performance during 75% moderate-intensity exercise, which may

be related to regular aerobic exercise habits. Further research is

needed to reﬁne the types of polyphenols, dosages, and exercise

protocols for different populations.

4.3 Supplementation time and

supplemental dose

This review suggests that prolonged use of speciﬁcpolyphenol

supplements may promote whole-body fat oxidation during moderate-

intensity exercise, which may beneﬁt aerobic endurance performance in

both professional athletes and sports enthusiasts. This may have

implications for how people utilize energy substrates and plan their

dietary strategies. In terms of supplementation strategies, only three out

of the 11 trials included acute supplementation before exercise. Acute

polyphenol supplementa tion was found to i mprove exercise

performance compared to continuous supplementation, although the

effect was not statistically signiﬁcant. In Martinez et al. (Martinez-

Noguera et al., 2019), acute ingestion of 500 mg of 2S-hesperidin

(Cardiose

) was administered to investigate its impact on athletic

performance. The best data from repeated sprint trials showed

signiﬁcant differences between Cardiose

and placebo in mean

power (+2.27%), maximum speed (+3.23%), and total energy

(+2.64%). While acute polyphenol supplementation improved

performance in repeated sprint tests, the average performance did

not differ signiﬁcantly from the placebo group. Similarly, in a

separate study, Deley et al. (Deley et al., 2017) explored the effects

of acute intake of grape and apple polyphenols on endurance exercise

capacity. Volunteers were randomly assigned to either take 500 mg of

polyphenols or a placebo the night before and 1 h before the test. The

mean duration of the maximum endurance test signiﬁcantly increased

in the polyphenol group compared to the placebo group (+9.7% ±

6.0%). The maximal perceived exertion was reached later with

polyphenols (+12.8% ± 6.8%). Another study (de Lima Tavares

Toscano et al., 2020) investigated the effects of a single dose of

grape juice on runners’ physical performance. In a running test up

to exhaustion (80% VO

2peak

) after consuming a placebo drink, athletes

ran for an average of 59.2 ± 27.8 min and covered an average of 12.6 ±

6.3 km. During the course after ingestion of purple grape juice, they

demonstrated signiﬁcantly enhanced performance, running for an

average of 9.2 min longer, representing an 18.7% improvement, and

a 1.9-km increase in distance compared to the placebo group. Among

the studies on acute supplementation included, this one exhibited the

most substantial improvement in athletic performance. However, in

terms of endurance exercise distance, long-term polyphenol intake

yielded a greater enhancement in athletic performance. Gaamouri et al.

(Gaamouri et al., 2019) designed a 6-week double-blind randomized

parallel fully controlled training study with pre- and post-

measurements. Analysis of aerobic activity for 6 weeks before and

after carob supplementation showed that the total distance covered

increased from 847.2 ± 473.9 m to 1,494.9 ± 619.2 m, representing an

increase of 92.43%. Regarding average power output, there was no

signiﬁcant change in average power output in Martinez et al. (Martinez-

Noguera et al., 2019) results which is acute polyphenols

supplementation. On the other hand, Roberts et al. (Roberts et al.,

2015) found in his 2015 study that supplementation of green tea extract

capsules for 4 weeks resulted in a notable increase in average power

output with dGTE by 17.9%, or 29.02 ± 5.53W from week 0 (162.06 ±

10.08W) to week 2 (191.08 ± 10.85W), and by 22.7%, or 36.85 ± 3.20W

from week 0 to week 4 (198.91 ± 8.61W). Metabolic parameters also

showed no signiﬁcant differences in these two trials. This may be due to

the small sample size, as only two articles existed. Because the

bioavailability of phenolic compounds in different supplements has

not been well established, the availability of supplements cannot be

determined before starting an exercise program. Caution should be

takenwhencomparingstudiesinvolving different types of polyphenols,

as their bioavailability may vary and subsequent interactions with other

nutrients taken at the same time may inﬂuence the results of the

comparison (Myburgh, 2014).

In this review, the average intake of polyphenols was 229. 04 mg/

day, which is equivalent to about 66 g of dark chocolate, 83 mg of

green tea, and 99 mg of mixed berries (blackcurrants, strawberries,

and blackberries). In these 11 trials, speciﬁc individuals and

combinations of polyphenols were used as interventions, and the

forms of intake varied. Five trials used capsules (Cook et al., 2015;

Roberts et al., 2015; Deley et al., 2017; Morgan et al., 2019; Nho and

Kim, 2022), three trials used water-soluble forms (Gaamouri et al.,

2019) or yoghurt (Howatson et al., 2022) as interventions, and there

was also oral consumption through snacks or canned forms (de

Lima Tavares Toscano et al., 2020; Roberts et al., 2023). Of these,

only one study supplemented carob pods in a water-soluble form,

and the participants in this study increased their endurance running

distance by 92. 43%, which was a signiﬁcantly greater improvement

compared to other supplementation methods (Gaamouri et al.,

2019). However, this supplementation method was only

mentioned in one study in the literature, making it difﬁcult to

draw qualitative conclusions. Further research is needed to address

the complex issue of the relative effects of different forms of

polyphenol intake on athletic performance. Analysis of the

performance indicators in the 11 studies showed that long-term

polyphenol supplementation can signiﬁcantly improve endurance

exercise performance. The most signiﬁcant indicator was a 92. 43%

increase in endurance running distance and this trial had the longest

duration of polyphenol supplementation of all 11 trials, lasting

6 weeks (Gaamouri et al., 2019). In contrast, another study found

that acute polyphenol supplementation resulted in an increase in

endurance running distance of approximately 18. 7% (de Lima

Tavares Toscano et al., 2020). This suggests that long-term

Frontiers in Physiology frontiersin.org13

Cao et al. 10.3389/fphys.2024.1369174

polyphenol supplementation may have a more pronounced effect

than acute supplementation.

It is important to note that existing research suggests that high doses

of antioxidant supplementation appear to have a detrimental effect on

endurance performance (Paulsen et al., 2014). High doses of antioxidant

supplements can shut down those cell signaling pathways sensitive to

redox changes, thereby reducing the synthesis of new musc le

mitochondria and the production of endogenous antioxidants (Kang

et al., 2009; Hawley et al., 2011; Feng et al., 2013). Crucially, the health

beneﬁts and performance enhancements brought about by endurance

training seem to be somewhat related to this cellular adaptation (Coffey

and Hawley, 2007; Ristow and Zarse, 2010). The results showed that

supplementation with high doses of antioxidants reduced the increase

in cytochrome c oxidase subunit IV(COX4) induced by endurance

training in the vastus lateralis muscle (Paulsen et al., 2014). While

antioxidant supplementation does not affect the short-term

improvement in endurance performance, it may negate the

beneﬁcial long-term adaptive effects of endurance training on cells.

This suggests that individuals who frequently engage in endurance

training should be cautious about using high doses of antioxidants. In

contrast, in this study, long-term supplementation with polyphenols

had more pronounced effects than acute or short-term ones. This may

be related to the dose of polyphenols included in the 11 studies and the

different bioavailability of polyphenols compared to other antioxidants

(Di Lorenzo et al., 2021), necessitating future research to explore

whether high-dose polyphenol supplementation affects those

signaling pathways related to improvements in endurance performance.

4.4 The potential of polyphenols

It should be noted that due to their complex structures and higher

molecular weights, polyphenols are not completely absorbed in the

gastrointestinal tract. Instead, they are primarily biotransformed into

low molecular weight, biologically active phenolic metabolites in the

large intestine through the action of the gut microbiota (Hill et al.,

2014; Ma and Chen, 2020). These low molecular weight metabolites

produce antimicrobial substances, regulate the host immune system,

and inhibit the production of bacterial toxins. They also have a certain

preventive effect on some chronic diseases (Cerdá et al., 2005; Espín

et al., 2013; Markowiak and Śliżewska, 2017). Furthermore,

polyphenols can modify the composition of the gut microbiota,

promoting the growth of beneﬁcial microbes, such as lactobacilli

and biﬁdobacteria, which are two major probiotics beneﬁcial for

human health (Wang et al., 2022). In interaction, the gut

microbiota also metabolizes polyphenols, producing biologically

active metabolites, such as short-chain fatty acids, which further

impact the host’shealth(Wang et al., 2022). The bioactivity of

polyphenols and their metabolites in the body is likely mediated

through these metabolites. These metabolites are generated in the

body, and recent studies have conﬁrmed that these molecules may

have antioxidant and anti-inﬂammatory properties (Di Lorenzo et al.,

2021). The bioavailability of polyphenols in the small intestine is low,

mainly due to their interactions with food matrices, liver-mediated

metabolic processes (both primary and secondary metabolism), and

metabolic processes in the gut and microbiota (Di Lorenzo et al.,

2021). However, the activity demonstrated by these compounds

through their metabolites in the organism suggests that long-term

intake of polyphenols can stabilize and alter the composition of the gut

microbiota, thus promoting more beneﬁcial health effects. The

aforementioned supplementation with polyphenols can improve

the utilization rate of fats as an energy substrate, and polyphenols

are also positively correlated with anti-lipogenesis. Polyphenols have

been shown to effectively activate the browning of adipose tissue,

reducing obesity and lipid accumulation by inducing the browning of

beige fat cells (Hu et al., 2020). Daily intake of beverages rich in

catechins can increase the density of brown adipose tissue in healthy

young women, supporting polyphenols’ role in brown fat genesis

(Nirengi et al., 2016). In mice on a high-energy diet, ferulic acid

accelerated thermogenesis and mitochondrial synthesis in brown

adipose tissue and inguinal white adipose tissue (Han et al., 2018).

Brown adipose tissue consumes energy more efﬁciently, contributing

to weight management and improved body fat distribution, which is

very important for maintaining good athletic performance and

endurance. In recent years, polyphenols have attracted attention

for their neuroprotective effects, showing potential effectiveness in

reversing neurodegenerative pathology and age-related cognitive

decline. Animal studies have shown that blueberries can improve

spatial memory deﬁcits in rats, (−)-epigallocatechin enhanced the

retention of spatial memory in mice, curcumin could break down

plaques and restore neurites in Alzheimer’s disease models, and

resveratrol reduced Aβ aggregation in rat hippocampal cells by

activating speciﬁc protein kinases (Casadesus et al., 2004; Dasgupta

and Milbrandt, 2007; Garcia-Alloza et al., 2007; Praag et al., 2007).

However, the direct link between polyphenols and improvements in

neural health has not been clearly established.

4.5 Limitations

This review has some limitations that should be considered. Firstly,

a meta-analysis could not be performed due to the heterogeneity in

study design, populations, training status/types, and supplementation

methods. Secondly, some studies used VO

2max

as a recognized

performance indicator, but some subjects may have reached

2peak

during testing due to their training habits and routines,

leading to inherent measurement errors that could potentially affect

the data (McArdle et al., 2006). Additionally, we did not classify the

participants, which to some extent affected the comparison of the

impact of polyphenols on exercise performance. Each of the 11 articles

included in this review had varying durations of intervention and small

sample sizes, making it difﬁcult to effectively conduct a qualitative

analysis of polyphenol supplementation. In addition, in the articles by

Martínez et al. (Martinez-Noguera et al., 2019)andWillemsetal.

(Willems et al., 2015) the participants were aware of the allocation

scheme or were made aware of it, which may have biased the results.

Furthermore, in Willems’sarticle(Willems et al., 2015), there was a

lack of complete reporting of the performance scores of each

participating subject, which could also introduce bias in the results.

There are several important considerations for future research. Firstly,

more emphasis should be placed on investigating the bioavailability of

polyphenols, as this may help to determine the optimal dosage and

supplementation methods for different types of exercise, and thus have

beneﬁcial effects on athletic performance. Secondly, considering

participant categorization and specialization is important. Further

investigations can ascertain the potential applications of

Frontiers in Physiology frontiersin.org14

Cao et al. 10.3389/fphys.2024.1369174

polyphenols and their energetic effects on various categories of

participants and specialized athletes. In addition, few studies have

included comprehensive dietary controls. As the sources of polyphenol

intake are diverse, efforts should be made to quantify the intake of

polyphenols in participants’ diets using placebo-controlled designs, as

individuals with low intakes may show more positive responses to

dietary interventions. This will help to better explain the

research ﬁndings.

5 Conclusion

In summary, the results of the 11 studies indicate that ﬂavonoid-

rich compounds, providing a total of 208 mg of polyphenols and

14.4 mg of ﬂavonoids per 40 g in a water-soluble form,

demonstrated the most noticeable improvement in exercise

performance during a 6-week supplementation period (Gaamouri

et al., 2019). Supplementation with polyphenols or polyphenol

complexes may improve aerobic endurance performance and

promote fat oxidation in the human body. However, there is not

enough research to conﬁrm the effects of polyphenols or polyphenol

complexes on other outcomes (cardiovascular, antioxidant, gender)

to draw deﬁnitive conclusions. Further research is needed to clarify

the potential beneﬁts of polyphenols or polyphenol complexes on

other indicators (dosage, timing, controversies).

Data availability statement

The original contributions presented in the study are included in

the article/Supplementary material, further inquiries can be directed

to the corresponding author.

Author contributions

GC: Conceptualization, Data curation, Investigation,

Writing–original draft. JZ: Data curation, Investigation,

Writing–original draft. BW: Writing–review and editing. YW:

Conceptualization, Funding acquisition, Project administration,

Supervision, Writing–review and editing.

Funding

The author(s) declare ﬁnancial support was received for the

research, authorship, and/or publication of this article. This work

was supported by the Fundamental Research Funds for the Central

Universities (2023GCZX005).

Conﬂict of interest

The authors declare that the research was conducted in the

absence of any commercial or ﬁnancial relationships that could be

construed as a potential conﬂict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors

and do not necessarily represent those of their afﬁliated

organizations, or those of the publisher, the editors and the

reviewers. Any product that may be evaluated in this article, or

claim that may be made by its manufacturer, is not guaranteed or

endorsed by the publisher.

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