Hydrogen gas: from clinical medicine to an emerging ergogenic molecule for sports athletes

Abstract

H2 has been clinically demonstrated to provide antioxidant and anti-inflammatory effects, which makes it an attractive agent in exercise medicine. Although exercise provides a multiplicity of benefits including decreased risk of disease, it can also have detrimental effects. For example, chronic high-intensity exercise in elite athletes, or sporadic bouts of exercise (i.e., noxious exercise) in untrained individuals, result in similar pathological factors such as inflammation, oxidation, and cellular damage that arise from and result in disease. Paradoxically, exercise-induced pro-inflammatory cytokines and reactive oxygen species largely mediate the benefits of exercise. Ingestion of conventional antioxidants and anti-inflammatories often impairs exercise-induced training adaptations. Disease and noxious forms of exercise promote redox dysregulation and chronic inflammation, changes that are mitigated by H2 administration. Beneficial exercise and H2 administration promote cytoprotective hormesis, mitochondrial biogenesis, ATP production, increased NAD⁺/NADH ratio, cytoprotective phase II enzymes, heat-shock proteins, sirtuins, etc. We review the biomedical effects of exercise and those of H2, and we propose that hydrogen may act as an exercise mimetic and redox adaptogen, potentiate the benefits from beneficial exercise, and reduce the harm from noxious exercise. However, more research is warranted to elucidate the potential ergogenic and therapeutic effects of H2 in exercise medicine.

Full text

REVIEW
Hydrogen gas: from clinical medicine to an emerging
ergogenic molecule for sports athletes
1
Tyler W. LeBaron, Ismail Laher, Branislav Kura, and Jan Slezak
Abstract: H
2
has been clinically demonstrated to provide antioxidant and anti-inflammatory effects, which makes it an attrac-
tive agent in exercise medicine. Although exercise provides a multiplicity of benefits including decreased risk of disease, it can
also have detrimental effects. For example, chronic high-intensity exercise in elite athletes, or sporadic bouts of exercise (i.e.,
noxious exercise) in untrained individuals, result in similar pathological factors such as inflammation, oxidation, and cellular
damage that arise from and result in disease. Paradoxically, exercise-induced pro-inflammatory cytokines and reactive oxygen
species largely mediate the benefits of exercise. Ingestion of conventional antioxidants and anti-inflammatories often impairs
exercise-induced training adaptations. Disease and noxious forms of exercise promote redox dysregulation and chronic inflam-
mation, changes that are mitigated by H
2
administration. Beneficial exercise and H
2
administration promote cytoprotective
hormesis, mitochondrial biogenesis, ATP production, increased NAD
+
/NADH ratio, cytoprotective phase II enzymes, heat-shock
proteins, sirtuins, etc. We review the biomedical effects of exercise and those of H
2
, and we propose that hydrogen may act as an
exercise mimetic and redox adaptogen, potentiate the benefits from beneficial exercise, and reduce the harm from noxious exercise.
However, more research is warranted to elucidate the potential ergogenic and therapeutic effects of H
2
in exercise medicine.
Key words: reactive oxygen species, antioxidants, molecular hydrogen, free radicals, exercise, inflammation, redox dysregulation,
anti-inflammatory, hormesis, mitochondria.
Résumé : Des données cliniques ont montré que l’H
2
a des effets antioxydants et anti-inflammatoires, ce qui en fait un agent
attrayant en médecine de l’exercice physique. Bien que l’exercice physique offre une multitude de bienfaits, y compris une
diminution du risque de maladie, il peut aussi avoir des effets délétères. Par exemple, les effets de l’exercice physique de haute
intensité de manière prolongée chez les athlètes d’élite, ou de pointes sporadiques d’exercice physique —c’est-à-dire de l’exercice
physique nocif —chez des personnes non entraînées, se résument à des facteurs pathologiques similaires comme l’inflammation,
l’oxydation et des dommages cellulaires, lesquels entraînent des maladies ou en sont le résultat. Paradoxalement, les cytokines
pro-inflammatoires et les dérivés réactifs de l’oxygène produits pendant l’exercice physique contribuent largement à la média-
tion des bienfaits de l’exercice physique. En outre, l’ingestion d’antioxydants et d’anti-inflammatoires classiques nuit souvent
aux modes d’action d’adaptation à l’entraînement mis en jeu pendant l’exercice physique. De fait, la maladie et les formes
nocives d’exercice physique favorisent le dérèglement redox et l’inflammation chronique, changements pourtant atténués par
l’administration d’H
2
. Effectivement, l’exercice physique bénéfique et l’administration d’H
2
favorisent l’hormèse cytoprotec-
trice, la biogenèse mitochondriale, la production d’ATP, l’augmentation du ratio NAD
+
/NADH, les enzymes cytoprotecteurs de
phase II, les protéines de choc thermique, les sirtuines, etc. En résumé, nous offrons une synthèse des effets biomédicaux de
l’exercice physique et de ceux de l’H
2
, et nous proposons que l’hydrogène puisse agir en tant que mimétique de l’exercice
physique et d’adaptogène redox, potentialiser les bienfaits de l’exercice physique bénéfique et atténuer les dommages causés par
l’exercice physique nocif. Il serait cependant justifié de procéder à plus de recherches en vue d’élucider les effets ergogènes et
thérapeutiques de l’H
2
en médecine de l’exercice physique. [Traduit par la Rédaction]
Mots-clés : dérivés réactifs de l’oxygène, antioxydants, hydrogène moléculaire, radicaux libres, exercice physique, inflammation,
dérèglement redox, anti-inflammatoire, hormèse, mitochondrie.
Introduction
Hydrogen gas may have potential as an ergogenic and therapeutic
molecule for sports athletes. The biomedical interest in molecular
hydrogen has grown exponentially since the publication of a pa-
per by Ohsawa et al. (2007). They reported that inhalation of only
2%–4% H
2
gas significantly reduced the cerebral infarct volumes in
a rat model of ischemia–reperfusion injury induced by middle
cerebral artery occlusion. The authors further demonstrated that
dissolved hydrogen in the media of cultured cells, at biologically
feasible concentrations, selectively reduced levels of toxic hy-
Received 1 February 2019. Accepted 27 March 2019.
T.W. LeBaron. Molecular Hydrogen Institute, Utah, USA; Centre of Experimental Medicine, Institute for Heart Research, Slovak Academy of Sciences,
Bratislava, Slovak Republic.
I. Laher. Department of Anesthesiology, Pharmacology and Therapeutics, Faculty of Medicine, The University of British Columbia, 217 - 2176 Health
Sciences Mall, Vancouver, BC V6T 1Z3, Canada.
B. Kura and J. Slezak.* Centre of Experimental Medicine, Institute for Heart Research, Slovak Academy of Sciences, Bratislava, Slovak Republic.
Corresponding author: Tyler W. LeBaron (email: LeBaronT@molecularhydrogeninstitute.com).
*Jan Slezak served as a Guest Editor; peer review and editorial decisions regarding this manuscript were handled by Tatiana Ravingerova.
1
This paper is part of a Special Issue of selected papers from the 5th European Section Meeting of the International Academy of Cardiovascular Sciences held
in Smolenice, Slovakia, on 23–26 May 2018.
Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from RightsLink.
797
Can. J. Physiol. Pharmacol. 97: 797–807 (2019) dx.doi.org/10.1139/cjpp-2019-0067 Published at www.nrcresearchpress.com/cjpp on 10 April 2019.

droxyl radicals (
•
OH), but did not decrease other physiologically
important reactive oxygen species (ROS) (e.g., superoxide, nitric
oxide, hydrogen peroxide) (Ohsawa et al. 2007). This is a critical
benefit for athletes because ROS play an active role not only in
injury and overtraining, but also in mediating the benefits of
exercise-induced training adaptations (Merry and Ristow 2016).
Although the research on molecular hydrogen is still in its in-
fancy, with only ≈1200 scientific publications on the subject, these
preclinical and clinical studies suggest that H
2
may have thera-
peutic potential, with no toxicity, in over 170 different human and
animal disease models (Ichihara et al. 2015;LeBaron et al. 2019).
Erratic and prolonged intense exercise may be considered a
potentially useful disease model due to the accompanying oxida-
tive stress, inflammation, muscle damage, and abnormal metab-
olites, which may strengthen the applications for H
2
in exercise
and sports performance. Not only does conventional antioxidant
supplementation fail to prevent these exercise-induced patholog-
ical changes, it may also negate exercise benefits. In contrast, we
hypothesize that, just as H
2
mitigates those pathological factors in
diseases, it may similarly attenuate those same factors when in-
duced by exercise, and may actually promote beneficial exercise
adaptations. Thus, we propose that due to these potential bene-
fits, combined with the current exercise studies on H
2
, hydrogen
is uniquely qualified as an ergogenic and therapeutic molecule for
exercise performance and sports medicine.
Exercise benefits
Exercise provides many benefits, including decreased risk of
diabetes, cardiovascular disease, cancer, and even premature
mortality (Levinger et al. 2015). On the molecular level, exercise
provides benefits by modulating signal transduction and via alter-
ing DNA acetylation and methylation patterns, which in turn
influences gene expression. Consequently, exercise increases en-
dogenous antioxidant levels (e.g., glutathione (GSH), superoxide
dismutase (SOD), catalase (CAT), etc.), neurotropic factors (e.g.,
brain-derived neurotropic factor), circulating adiponectin levels,
enhances the expression of glucose transporter type 4 transport-
ers, induces mitochondrial biogenesis, promotes DNA repair
mechanisms, and provides a host of other physiological benefits
(Tang et al. 2005;Gomez-Pinilla et al. 2011;Gomes et al. 2012).
Although the benefits of exercise are well documented, the exact
underlying molecular mechanisms of how exercise affords these
therapeutic effects have remained unclear. Recent research suggests
that the exercise-induced increase of endogenously produced reac-
tive molecules may be a primary mediator for these beneficial
effects (Gomes et al. 2012). This appears to be at odds with an
earlier proposed model of aging and disease known as the “Free
Radical Theory of Aging”. This theory of aging was proposed in the
1950s by Denham Harman, and was largely based on the strong
correlations between oxidative stress and diseases (Harman 2009).
Indeed, some have suggested that oxidative stress plays a caus-
ative role in the pathogenesis of virtually every disease (Liochev
2013).
Oxidative stress
Oxidative stress exists when the number of oxidants and reac-
tive molecules overcomes the body’s endogenous enzymatic and
nonenzymatic antioxidant self-defense systems (Bentley et al.
2015). Reactive molecules include ROS and reactive nitrogen spe-
cies. ROS is a category that includes radicals and nonradical chem-
ical species. Free radicals are chemical species that contain an
unpaired electron; for example, hydroxyl radicals (
•
OH), superox-
ide anion radicals (
•
O
2−
), alkoxyl radicals (R-O
•
), peroxyl radicals
(R-OO
•
), carbon radicals (R-C
•
), and various reactive nitrogen spe-
cies (e.g., nitric oxide, NO
•
), and thiyl radicals (RS
•
). Nonradical
reactive molecules include hydrogen peroxide (H
2
O
2
), singlet
oxygen (
1
O
2
), and various reactive nitrogen species (e.g., peroxyni-
trite (ONOO
−
), nitrogen dioxide (NO
2
), dinitrogen trioxide (N
2
O
3
))
(Palmieri and Sblendorio 2006;Jones 2008). Most ROS are pro-
duced in the electron transport chain of the mitochondria, pri-
marily at complex 1, and not 3, as was commonly believed (Liu
et al. 2002). Other sites of ROS generation include NADPH oxidase,
nitric oxide synthase, xanthine oxidase, cytochrome p450, alde-
hyde oxidase, and heme proteins, etc. (Halliwell and Gutteridge
2015). The increased metabolism and the exercise-induced activa-
tion of these systems result in a significant increase in ROS pro-
duction.
ROS regulation
Importantly, these reactive molecules can either have noxious
or beneficial effects, depending on their (i) identity, (ii) concentra-
tion, (iii) location, and (iv) duration. For example, under normal
metabolic conditions, superoxide radicals are constantly being
formed by single-electron reduction of molecular oxygen in the
electron transport chain of the mitochondria, in nuclear and
plasma membranes via NADPH oxidases, in the endoplasmic re-
ticulum for protein folding, and in macrophages (Finkel 2011).
Superoxide production is increased during immune responses, as
it is essential for killing pathogens, and increasing levels of in-
flammatory cytokines, and for the formation of NOD-like receptor
prin domain-containing 3 inflammasome (Finkel 2011). Similarly,
superoxide formation is increased during bouts of exercise due to
the increased oxygen intake. Exercise-induced superoxide acts as an
important signalling molecule that activates various transcription
factors, resulting in improved exercise capacity (Gomes et al. 2012).
The concentration of superoxide is regulated within a narrow
range by controlling its production and its clearance (Halliwell
and Gutteridge 2015). Superoxide can be dismutated by the body’s
antioxidant enzyme SOD to form H
2
O
2
. The produced H
2
O
2
,as
another important signalling molecule, can further regulate gene
expression and induce favourable cellular changes before being
converted to water and O
2
by CAT (Jones 2008). If the concentra-
tion of superoxide or H
2
O
2
exceeds regulatory systems, then oxi-
dative stress occurs. The higher levels may also result in an
increased production of toxic hydroxyl radicals (
•
OH) via the Haber–
Weiss and Fenton reactions (eqs. 1 and 2). Ferrous iron and super-
oxide can then be regenerated (eq. 3) and participate in eqs. 1 and 2,
respectively, which further propagates the production of hy-
droxyl radicals (Halliwell and Gutteridge 2015).
(1) Fe3⫹⫹•O2¡Fe2⫹⫹O2
(2) Fe2⫹⫹H2O2¡Fe3⫹⫹OH⫺⫹•OH
(3) Fe3⫹⫹H2O2¡Fe2⫹⫹•O2⫺⫹2H⫹
Due to their high reactivity, hydroxyl radicals (
•
OH) react with essen-
tially any biomolecule at a diffusion-controlled rate (≈10
10
·M
−1
·s
−1
),
which makes them so damaging. Therefore, the regulation of the
signalling molecules superoxide and hydrogen peroxide is essen-
tial to reduce the production of hydroxyl radicals.
The nitric oxide radical (NO
•
) is also an essential signalling mol-
ecule, and is needed for endothelial function (e.g., vasodilation),
gene expression, and cell proliferation (Nathan and Xie 1994), and
is produced near its targets (Clements et al. 2014). However, simi-
lar to superoxide, when its concentration is too high, such as from
hyperactivation of inducible nitric oxide synthase, then excess NO
•
can combine nearly instantly with superoxide to form pernicious
peroxynitrite molecules (Brown and Neher 2010). Peroxynitrite is
a stronger oxidant than either nitric oxide or superoxide, and
besides being able to oxidize proteins, lipids, and DNA, is also a
non-Fenton source of toxic hydroxyl radicals (Pacher et al. 2007).
These 2 oxidants (i.e., ONOO
−
and
•
OH) have no known physiolog-
798 Can. J. Physiol. Pharmacol. Vol. 97, 2019
Published by NRC Research Press

ical benefit, and easily oxidize cellular biomolecules leading to
disease, injury, and impaired athletic performance.
Disproportionate levels of ROS generation either from disease
or from vigorous exercise can rapidly deplete the body’s antioxi-
dant system (e.g., SOD, GSH, vitamin C, etc.) leading to oxidative
stress and its subsequent toxic consequences (Finkel 2011). The
location of ROS formation is also critical in determining whether
they will have a beneficial or a noxious effect. Deliberate super-
oxide production via NO
x
systems or within the mitochondria
often occurs near redox-sensitive transcription factors and phos-
phatases (D’Autréaux and Toledano 2007). For example, there are
specifically located aquaporins through which the produced H
2
O
2
can transverse, permitting interaction with various biomolecules
(e.g., phosphatases for growth factor signalling (Juarez et al. 2008))
before being converted to water and oxygen by glutathione per-
oxidase or CAT (Finkel 2011). The colocalization of the oxidant-
producing system with the intended target affords specificity of
the oxidant, thus ensuring a higher probability for beneficial ef-
fects (D’Autréaux and Toledano 2007;Dickinson and Chang 2011).
Redox dysregulation
Reactive molecules have both deleterious disease-causing ef-
fects, and essential and therapeutic disease-preventing effects
(Levinger et al. 2015). This paradoxical nature of oxidant signalling
may be considered a form of hormesis, in which low doses of
potentially harmful stress result in cytoprotective cellular adap-
tations. Thus, the 2 opposing effects of oxidants on health are not
simply paradoxical, but are homeostatically interconnected and
interdependent. Redox homeostasis is required for normal cellu-
lar and bodily function. The key issue is not the presence or ab-
sence of oxidants and antioxidants in inducing detrimental
consequences, but the harmful disturbance to the delicate ho-
meostasis between oxidation and reduction (Gomes et al. 2012).
This disturbance or dyshomeostasis is referred to as redox dys-
regulation.
Paradoxically, it is possible to have too much and too little
oxidation at the same time within the same cell. For example,
aging is associated with excessive oxidation in the cytosol, but a
loss of oxidizing potential in the endoplasmic reticulum, which is
essential for the proper folding of proteins (Feleciano and Kirstein
2016). In contrast to focusing exclusively on free radicals as being
responsible for aging and disease, redox dysregulation appears to
be a more accurate proposition.
ROS-mediated exercise benefits
Exercise naturally elicits the hormesis effect due to the tran-
sient spikes in ROS production, and thus improves optimal redox
homeostasis and mitigates against redox dysregulation (Ristow
and Zarse 2010). This helps explain why many of the benefits of
exercise are thought to be mediated by exercise-induced ROS pro-
duction, which activates a plethora of transcription factors and
modulates various signal transduction pathways (Finkel 2011). Ex-
ercise greatly increases oxygen demand and thus also subsequent
ROS production. It has been estimated that 0.2%–2% of the O
2
we
breathe is converted into various ROS (Balaban et al. 2005). ROS is
also produced under other types of hypoxia–ischemia type condi-
tions and in sarcomeres of exercising muscles (Powers et al. 2011).
Parabolic nature of exercise
Similar to disease remediation, wound healing, and injury re-
covery, the relationship between exercise-induced ROS benefits
and exercise-induced ROS damage follows a parabolic type func-
tion as shown in Fig. 1. An increasing level of ROS facilitates injury
healing and beneficial exercise adaptations, but excessive ROS has
the opposite effect. This cytotoxic effect can occur with prolonged
high-intensity exercise (Fisher-Wellman and Bloomer 2009;Merry
and Ristow 2016). Elite athletes frequently exercise chronically at
these high intensities, which consequently increases ROS produc-
tion leading to cytotoxic injuries and a decrease in endogenous
antioxidant status (Fisher-Wellman and Bloomer 2009). The
chronic assault of ROS can result in potentially detrimental cellu-
lar adaptations for the athlete. For example, during exercise,
mediation of vasodilation switches from NO
•
to mitochondrial-
derived H
2
O
2
(Durand and Gutterman 2014). Excessive ROS pro-
duction and subsequent cellular damage also occurs in the
elderly (due to loss of endogenous antioxidant levels) (Evans
2000), and in “weekend warriors”, where their body has not made
necessary adaptations to cope with the stresses of erratic and (or)
overly intense exercise bouts (Davies et al. 1982;Evans 2000;Urso
and Clarkson 2003).
Antioxidant supplementation
Exercise-induced excessive ROS production provides a rationale
for the ingestion of exogenous antioxidant supplements by many
athletes. However, several clinical trials on antioxidant supple-
mentation report that their use is not only ineffective, but can, in
fact, be deleterious. Several studies suggest that antioxidants can
negate training benefits, such as vascularization and mitochon-
drial biogenesis (Merry and Ristow 2016). Studies of human ath-
letes are equivocal, showing that antioxidant supplementation
can have ergogenic, ergolytic, or neutral effects on exercise per-
formance (Fisher-Wellman and Bloomer 2009). However, the re-
sults in those studies showing potential ergogenic effects of
antioxidant supplementation (Lafay et al. 2009;Braakhuis et al.
2013) are obfuscated by their potential nonradical scavenging ac-
tions (e.g., effectors of signal transduction). For example, the poly-
phenolic compounds in tea, grapes, and other plants often have
pharmacological effects in cells. They do not act simply as radical
scavengers, but exist in the cell as important sensors and effectors
of key redox-regulated pathways (Finkel 2011).
Several well-designed human studies show that daily antioxidant
supplementation (e.g., alpha tocopherol) can impair exercise perfor-
mance (Sharman et al. 1971;Olesen et al. 2014). An 8-week study
found that vitamin C blunted the exercise-induced increase in max-
imal oxygen consumption (V
˙O
2
max) by 50% (Gomez-Cabrera et al.
2008). Another study showed V
˙O
2
max improved only in the placebo
group (Morrison et al. 2015), and biochemical analysis of muscle
biopsy revealed that the exercise-induced upregulation in GSH
and PGC-1␣, a marker of mitochondrial biogenesis, was abolished
by antioxidant ingestion (Morrison et al. 2015). Similarly, an 11-
Fig. 1. Hypothetical relation between increasing levels of reactive
oxygen species (ROS) production and various health benefits.
Horizontal axis follows ROS production from sedentary to elite
athletes and (or) various disease conditions (e.g., ischemia–reperfusion).
LeBaron et al. 799
Published by NRC Research Press

week study with 54 subjects found that compared with placebo,
ingestion of 1000 mg of vitamin C and 235 mg of vitamin E during
training blunted the endurance-training-induced increases of im-
portant biomolecules, such as cytochrome c oxidase (COX4), per-
oxisome proliferator-activated receptor gamma coactivator 1-alpha
(PGC-1␣), cell division control protein 42, and mitogen-activated
protein kinase 1 (Paulsen et al. 2014). These data are in agreement
with another study showing that several antioxidant enzymes (i.e.,
SOD1, SOD2, glutathione peroxidase (GPx1), and CAT), and mitochon-
drial biogenesis (i.e., PGC-1␣), were only increased in untreated athletes,
i.e., in the absence of antioxidant supplementation (Ristow et al. 2009).
Similar negative effects have been reported by others (Wray et al. 2009;
Gliemann et al. 2013,2014).
Inflammation and injury
Chronic exercise also increases levels of inflammation by up-
regulating various pro-inflammatory mediators (Pedersen et al.
2007). Many of these increases are also associated with disease
conditions in which excessive levels of inflammation further dam-
age tissue and delay healing (Hotamisligil 2006). Similar to the
effects of acute and chronic physical activity on oxidative stress,
regular exercise reduces systemic inflammation, whereas chronic
high-intensity exercise training increases inflammation (Gleeson
2007). Athletes engaged in chronic and prolonged exercise train-
ing at high intensities can exhibit exercise-induced immunode-
pression, thus also increasing their risk for infection (Gleeson
et al. 2004).
The biphasic relationship between the beneficial and noxious
effects of myokines (cytokines secreted from skeletal muscle) fol-
lows a similar paradoxical pattern, as does exercise-induced ROS
generation (Handschin and Spiegelman 2008) (see Fig. 1). For ex-
ample, the myokines interleukin (IL)-6, IL-1, IL-8, IL-15, etc., se-
creted from exercising muscle fibers mediate some of the benefits
of exercise (Pedersen et al. 2007). These myokines not only medi-
ate the benefits (e.g., increased expression of p38-AMPK, ERK1/2,
PGC-1␣) to the exercising muscles themselves, but they also pro-
vide systemic beneficial effects on nonskeletal muscle tissue (e.g.,
improved glucose homeostasis) (Handschin and Spiegelman 2008).
However, prolonged elevation of these pro-inflammatory mediators
(i.e., cytokines, tumor necrosis factor-␣, chemokines, etc.) increases
the risk of diseases such as cancer, diabetes, neurodegeneration,
sarcopenia, and others (Hotamisligil 2006), as well as injury and im-
paired athletic performance (Handschin and Spiegelman 2008).
Chronic ingestion of anti-inflammatory agents is prevalent
among both those with debilitating diseases, and with athletes
trying to train or compete with various injuries. Estimated daily
use of nonsteroidal anti-inflammatories in the general population
is around 4%, and in elite athletes as high as 35% (Paoloni et al.
2009). However, in addition to the potential toxic side effects of
prolonged use of steroidal and nonsteroidal anti-inflammatory
agents, there is also evidence suggesting that their chronic use
may also blunt exercise training benefits similar to antioxidants
(Schoenfeld 2012;Urso 2013).
Effects of molecular hydrogen
In contrast to these conventional antioxidants and anti-
inflammatories, the physicochemical properties and biomedical
studies of molecular hydrogen suggest that H
2
may be useful in
mitigating the effects of excessive ROS and inflammation (Ohta
2015;Slezák et al. 2016;Nogueira et al. 2018), without abolishing
the desired exercise training adaptations and benefits. This is be-
cause H
2
is a stable molecule incapable of reacting with important
reactive signalling molecules under biological conditions without
a catalyst. It hasbeen proposed that, although H
2
cannot neutralize
important ROS, it can selectively scavenge cytotoxic hydroxyl rad-
icals, and to a lesser extent peroxynitrite (Ohsawa et al. 2007),
which is exactly what is most needed for athletes. Although the
2
nd
-order reaction rate constant between hydroxyl radicals and H
2
(4.2 × 10
7
·M
−1
·s
−1
) is about 3 orders of magnitude lower than that
between other more abundant nucleophilic cellular components,
it is clear that H
2
reduces the markers (e.g., 3=-p-(aminophenyl)
fluorescein, 3=-p-(hydroxyphenyl) fluorescein) for these oxidants
(Ohta 2015). Molecular hydrogen has become an attractive agent
in the biomedical field by acting as a gaseous-signalling modula-
tor that effectively decreases oxidative stress and inflammation
(Dixon et al. 2013). Molecular hydrogen has been shown to have
therapeutic potential in over 170 different animal and human
disease models, and in essentially every organ of the human body.
Several animal studies have shown that H
2
is effective at increas-
ing resilience and mitigating the negative effects of acute and
chronic stress such as inflammation, elevated ROS, and anxiety
and depressive-like behaviours (Nagata et al. 2009;Slezak et al.
2015;Zhang et al. 2016;Gao et al. 2017).
Erratic or prolonged intense exercise may be considered a
model for disease due to the many parallels and common patho-
logical factors (i.e., ROS, inflammation, metabolic changes, etc.)
between them. For example, in a rat study comparing early aerobic
exercise with and without H
2
administration as preconditioning to
protect against myocardial injury induced by acute myocardial
infarction, it was demonstrated that H
2
was as effective as, and
sometimes more effective than, early aerobic exercise, and the
greatest benefit was often the combination (e.g., infarct size,
troponin 1, SOD, CAT, GSH, total antioxidant status, malondialde-
hyde (MDA), creatine kinase, and mitochondrial protein translo-
case of outer membrane 20, translocase of inner membrane 23)
(Feng et al. 2018). Therefore, H
2
may be beneficial for elite and
nonelite athletes because (i) administration of H
2
elicits many of
the same benefits provided by exercise, thus acting as an “exercise
mimetic”, and (ii) just as H
2
restores redox homeostasis, prevents
pathological changes, and mitigates excessive inflammation aris-
ing from and induced by disease, it may similarly have those
protective and therapeutic effects against noxious forms of exer-
cise (Ostojic 2014;Nogueira et al. 2018). Table 1 summarizes some
of the biomolecular changes present in disease, beneficial or nox-
ious forms of exercise, and by H
2
administration. The changes in
disease conditions are pathological in nature, and do not repre-
sent any specific disease, but represent common findings of dis-
eases in general (Hotamisligil 2006). The reader is referred to
several reviews on diseases for more details on these detrimental
changes (Hotamisligil 2006;Gleeson 2007;Pedersen et al. 2007).
For exercise, the changes are either negative or positive, which
would depend on the frequency, intensity, duration, and recov-
ery. For example, it is not uncommon for athletes to push them-
selves to extreme levels of chronic prolonged intense training, or
for even untrained individuals to complete a marathon or other
physically demanding events (e.g., weekend basketball). These
chronic or erratic intense activities can directly damage muscle
tissue, resulting in cell death and decreased mitochondrial func-
tion or number, and (or) other pathological changes. However,
regular optimal exercise induces beneficial changes to these bio-
markers (i.e., increases or decreases) compared with the biomark-
ers of sedentary individuals, and thus provides protection against
their pathological changes in maintaining and improving optimal
homeostatic levels (Gleeson et al. 2004).
The arrows in Table 1 that represent the changes by H
2
admin-
istration indicate the respective attenuation of the pathologically
induced changes compared with control. These changes of H
2
administration were gathered from data involving humans and
animals (Dixon et al. 2013;LeBaron et al. 2019;Nicolson et al. 2016),
and are not directly quantified or compared with respect to each
other or exercise. Thus, caution should be used when interpreting
the table. However, the improved homeostasis and cellular viabil-
ity from H
2
administration has been reported in different animal
species (e.g., rodent, dog, horse, pig, etc.) and in many different
800 Can. J. Physiol. Pharmacol. Vol. 97, 2019
Published by NRC Research Press

animal disease models, as well as in clinical human studies (Zhai
et al. 2014;Ichihara et al. 2015).
H
2
acts as a hormetic effector to improve redox
status
Intriguingly, hydrogen does not always reduce markers of oxi-
dation, but it appears that it only reduces excessive levels. The fact
that H
2
does not scavenge ROS, and only decreases excessive levels
of ROS, makes it a safe and effective medical gas for use in clinical
management and also to preserve the benefits and reduce the
harm of sporadic or chronic intense exercise. Not only does H
2
reduce excessive ROS production, but it may also have beneficial
mild pro-oxidant properties, by exerting hormetic benefits simi-
lar to those produced by exercise. Some studies show that the
therapeutic and neuroprotective benefits of H
2
are also correlated
with slightly increased levels of MDA, a marker of lipid peroxida-
tion (Eckermann et al. 2011), even in the sham group (Matchett
et al. 2009). We reported similar changes in rats, where H
2
pre-
vented irradiation-induced increases in tumor necrosis factor-␣
and MDA. But when H
2
was administered alone, tumor necrosis
factor-␣initially increased above control, and then decreased and
remained below both the irradiated group and the nonirradiated
control, whereas MDA tended to initially decrease then increase
(Kura et al. 2019); thus, demonstrating that, although H
2
primarily
reduces MDA, sometimes its therapeutic effects are associated
with transiently increased levels of MDA. Similarly, some of the
benefits of H
2
in plants are also mediated by increases in ROS
production (Xie et al. 2014). Furthermore, pretreatment of
SH-SY5Y cells with H
2
protected them from subsequent oxidative
stress induced by H
2
O
2
(Murakami et al. 2017). In this case, H
2
acted as a mitohormetic effector by transiently increasing mito-
chondrial superoxide production, followed by an upregulation of
Nrf2 transcription and induction of other cytoprotective phase II
proteins (Murakami et al. 2017;Kura et al. 2018). We recently
demonstrated that short-term inhalation of H
2
mildly increased
urinary 8-hydroxy-2=-deoxyguanine (8-OHdG) in patients with
Parkinson’s disease by 16% (p= 0.02) (Hirayama et al. 2018). This is
significantly less than the several hundred percent increase seen
in various diseases, and comparable with a mild bout of exercise
training (Hirayama et al. 2018). In contrast, a 4-week open label
cross-over study in patients with rheumatoid arthritis, found that
ingestion of hydrogen-rich water (HRW) significantly decreased
8-OHdG by 14.3% (p< 0.01), and remained below baseline for an
additional 4 weeks during the washout period (Ishibashi et al.
2012). This illustrates the emerging pattern that H
2
has dual ef-
fects depending on the situation. In addition to the ROS-induced
hormesis, H
2
has paradoxically been reported to provide thera-
peutic effects via transiently activating the NF-␬B/Bcl-xL pathway
in the early phase (Zhuang et al. 2013), which may also be a form
of hormesis (Hirayama et al. 2018). Lastly, it has been reported that
H
2
can induce heat-shock response (Nishiwaki et al. 2018) and the
mitochondrial unfolded protein response (Sobue et al. 2017).
These may also be considered forms of hormesis that are also
induced by exercise.
These 2 opposing effects of hydrogen (e.g., increased and de-
creased ROS production) are not mutually exclusive. Depending
on the challenge, timing, and need, hydrogen treatment appears
to perform either function to help maintain optimal redox ho-
meostasis. Hydrogen seems to act as a redox adaptogen at main-
taining redox homeostasis either by acting hormetically and (or)
via modulating redox-sensitive processes.
Methods of H
2
administration
There are several methods for hydrogen gas administration in-
cluding inhalation of H
2
gas (Hayashida et al. 2008), tube feeding
of H
2
-rich solution (Li et al. 2013), intravenous injection of H
2
-rich
saline (Cui et al. 2014), H
2
-rich dialysis solution for hemodialysis
(Nakayama et al. 2010), hyperbaric H
2
chamber (Dole et al. 1975),
bathing in H
2
-rich water (Kato et al. 2012), increasing H
2
produc-
tion by intestinal bacteria (Chen et al. 2013), topical application
(Ostojic et al. 2014), oral ingestion of hydrogen-producing tablets
(LeBaron et al. 2019;Ostojic et al. 2018), and simply drinking HRW
(Nakao et al. 2010). Regardless of the mode of administration, the
cellular bioavailability of molecular hydrogen is extremely high
due to its unique physicochemical properties. Its small size, low
mass, neutral charge and nonpolar nature, coupled with its high
rate of diffusion, allow it to easily penetrate cellular biomem-
branes and diffuse into the mitochondria and nucleus (Nicolson
et al. 2016;Ohta 2015).
Hydrogen can be dissolved in water up to 0.8 mM (1.6 mg·L
−1
)at
standard ambient temperature and pressure. A concentration of
1.6 mg·L
−1
may not seem significant, but because H
2
is the lightest
and smallest molecule, it should be compared using moles rather
than mass. Ingestion of1LofH
2
-saturated water provides more
Table 1. Biological markers in disease, by exercise (negative and positive), and by H
2
treatment.
Biological markers Disease
Exercise
H
2
Negative Positive
Antioxidant status: BAP, SOD, GSH, CAT, GPx, GST, Nrf2, HO-1 ↓↓ ↑ ↑
Vascular function: eNOS, DDAH2 ↓↓ ↑ ↑
Brain effects: CREB, BDNF ↓↓ ↑ ↑
Mitochondrial function: ATP, membrane potential, complexes 1–5, PGC1-␣↓↓ ↑ ↑
Miscellaneous effects: GLUT4, TST, SIRT3, AMPK, NAD
+
/NADH ↓↓ ↑ ↑
Inflammatory response: TNF-␣, ILs1–20, NFATC1, COX-2, NF-␬B, NLRP3 ↑↑ ↓ ↓
Oxidative stress: MDA, d-ROM, CRP, 8OHdG, 4HNE, TBARS, NTY ↑↑ ↓ ↓
Tissue damage: Caspase-3,-8,-9,-12, AST, ALT, BUN, Cr, LDH ↑↑ ↓ ↓
Vascular: nNOS, iNOS ↑↑ ↓ ↓
Note: When interpreting the above data, note that the effects of H
2
treatment were gathered from data involving humans and
animals and are not directly quantified or compared with respect to each other or exercise. BAP, biological antioxidant potential; SOD,
superoxide dismutase; GSH, glutathione; CAT, catalase; GPx, glutathione peroxidase; GST, glutathione-S-transferase; Nrf2, nuclear
factor erythroid 2–related factor 2; HO-1, heme oxygenase-1; eNOS, endothelial nitric oxide synthase; DDAH2, dimethylarginine
dimethylaminohydrolase; CREB, cAMP response element binding protein; BDNF, brain-derived neurotropic factor; PGC1-␣, peroxi-
some proliferator-activated receptor-␥coactivator-1␣; GLUT4, glucose transporter type 4; TST, testosterone; SIRT3, sirtuin 3; AMPK,
AMP-activated protein kinase; TNF-␣, tumor necrosis factor-␣; ILs1–20, interleukins 1–20; NFATC1, Nuclear Factor Of Activated T-Cells
1; COX-2, cyclooxygenase-2; NF-␬B, nuclear factor kappa light chain enhancer of activated B cells; NLRP3, NOD-like receptor prin
domain-containing 3; MDA, malondialdehyde; d-ROM, diacron reactive oxygen metabolite; CRP, C-reactive protein; 8OHdG,
8-hydroxy-2=-deoxyguanine; 4HNE, 4-hydroxynonenal; TBARS, thiobarbituric acid reactive substances; NTY, nitrotyrosine; AST, aspar-
tate aminotransferase; ALT, alanine aminotransferase; BUN, blood urea nitrogen; Cr, creatinine; LDH, lactate dehydrogenase; nNOS,
neural nitric oxide synthase; iNOS, inducible nitric oxide synthase.
LeBaron et al. 801
Published by NRC Research Press

“therapeutic moles” than would ingestion of a 100 mg dose of
vitamin C (0.79 millimoles H
2
vs. 0.57 millimoles vitamin C). Al-
though, the amount of H
2
ingested from inhalation of H
2
gas can
be many times higher than from ingestion of HRW, drinking
HRW is often as effective as, and in some cases more effective
than, inhalation (Ito et al. 2012;Ohno et al. 2012). This is likely
attributed to hydrogen’s activity as a signal modulator (Ichihara
et al. 2015). HRW can be prepared by bubbling H
2
gas into water
under pressure, electrolysis of water (2H
2
O¡2H
2
+O
2
), and also
by reaction with metallic magnesium (Mg + 2H
2
O¡H
2
+ Mg(OH)
2
)
or other metals. Several products from ready-to-drink beverages
in aluminum pouches and cans and electrolytic devices to H
2
-
producing tablets and inhalation machines, are readily available
to consumers. However, not all products may produce or contain
concentrations of H
2
equivalent to or with the stability of those
used in human studies.
Human studies with H
2
administration
There are a limited number of clinical human studies to con-
firm the promising effects observed in laboratory animals. How-
ever, the approximately 60 studies in humans published so far
strengthen hydrogen’s potential as a feasible therapeutic agent.
These clinical studies have demonstrated beneficial effects in a
wide range of diseases including metabolic syndrome (Nakao et al.
2010), diabetes (Kajiyama et al. 2008), hyperlipidemia (Song et al.
2013), Parkinson’s disease (Yoritaka et al. 2013), cognitive impair-
ments (Nishimaki et al. 2018), rheumatoid arthritis (Ishibashi et al.
2012), chronic hepatitis B (Xia et al. 2013), vascular function (Sakai
et al. 2014), exercise performance (Ostojic´ et al. 2011), and others
(Ichihara et al. 2015). Currently, inhalation of hydrogen gas is
being clinically investigated in post-cardiac arrest patients in a
large 360-patient multicentered study with promising prelimi-
nary results (Ono et al. 2017). Animal studies suggest that H
2
inha-
lation may be more effective than conventional hypothermia at
mitigating the ischemia–reperfusion injury following cardiac re-
suscitation (Katsumata et al. 2017).
Table 2 summarizes the known studies on hydrogen admin-
istration and exercise in humans and animals, illustrating
hydrogen’s potential benefit in exercise medicine and sports per-
formance. In a double-blinded placebo-controlled cross-over trial
of 10 elite soccer players (20.9 ± 1.3 years), subjects ingested 1.5 L of
HRW (≈1 mM) prior to exercise (Aoki et al. 2012). Athletes under-
took ergometer cycling at 75% of V
˙O
2
max for 30 min, followed by
performing 100 repetitions of maximal isokinetic knee extensions
to evaluate peak torque and muscle activity as indicators of fa-
tigue. Peak torque was significantly decreased by 20%–25% after
40–60 contractions in the placebo group, but was not statistically
reduced in the HRW group, suggesting that H
2
attenuated the
exercise-induced decline of muscle function. Additionally, HRW
reduced the increase in blood lactate levels that occurred post-
cycling (reduction of ⬃1 mM, p< 0.05). Lactate production, although
not directly responsible for acidosis or fatigue, is correlated with
both events as it represents a shift from ATP derived from aerobic
respiration (in the mitochondrial electron transport chain) to
substrate-level phosphorylation (in glycolytic anaerobic metabo-
lism). The ability of the athletes to maintain a similar exercise
output with reduced lactate levels may suggest improved mito-
chondrial function, increased rates of NADH/NAD
+
recycling, or
lactate metabolism. The decreased lactate levels were also re-
ported in a clinical study in patients with mitochondrial myopa-
thies (Ito et al. 2011). Of interest is that the slightly elevated levels
of oxidative markers post-exercise in the elite soccer players were
not attenuated, and were even mildly elevated by HRW (no signif-
icant changes in diacron reactive oxygen metabolites (d-ROMs) or
biological antioxidant potential (BAP)), suggesting that, unlike the
case of conventional antioxidant use, hydrogen should not abol-
ish, put perhaps increase, beneficial training adaptations. The
authors concluded that replacement of regular water with HRW
as a hydration strategy may prevent the adverse effects associated
with heavy exercise (Aoki et al. 2012).
In another double-blinded randomized cross-over design,
18 athletes consumed 1 L·day
−1
of HRW; there were decreased maxi-
mal rates of perceived exertion and reduced lactate production at
the critical running speed (8.1 miles·hour
−1
; 1 mile = 1.609 344 km)
during maximal exercise, without increases in serum antioxidant
capacity (Ostojic´ et al. 2011;Ostojic 2014). Another double-blinded
placebo-controlled cross-over study with 9 subjects reported that
bathing in HRW for 20 min significantly decreased delayed onset
muscle soreness after downhill running (p< 0.033), without sig-
nificantly reducing the markers of oxidation (i.e., MDA, d-ROMs)
(Kawamura et al. 2016).
The lack of difference in oxidative markers were also seen in a
study of 5 thoroughbred horses undergoing maximum levels of
treadmill exercises to exhaustion (Tsubone et al. 2013). Compared
with the placebo group, the pre-exercise oxygen metabolites
(d-ROMs) tended to be lower in the HRW group, but then signifi-
cantly increased immediately post-exercise (p< 0.001 vs. p< 0.05).
The BAP increased similarly in both groups. However, after
30 min, the BAP/d-ROMs ratio was still elevated in the placebo
group (p< 0.05), but normalized in the HRW group (Tsubone et al.
2013). This earlier recovery of the BAP/d-ROMs ratio in the HRW
group suggests less radical damage and faster recovery after an
intense exercise session. However, a similar follow-up study with
13 thoroughbred horses (Yamazaki et al. 2015) reported that, al-
though H
2
similarly did not reduce d-ROMs, it did significantly
reduce 8-OHdG immediately after, and 1, 3, and 24 h post-exercise
(p< 0.01, p= 0.0196, p< 0.01, and p< 0.01, respectively). This
marker, 8-OHdG, was significantly increased above baseline post-
exercise, and remained elevated throughout the 24 h in the pla-
cebo group; whereas in the H
2
group, it did not significantly
change from its baseline level (Yamazaki et al. 2015).
It is important to note that these studies used trained athletes
(or horses), whose bodies and cells may have already adapted to
combat the exercise-induced ROS production. Several double-
blinded human studies involving untrained subjects show that H
2
supplementation increased antioxidant enzymes (e.g., GSH, SOD,
etc.) and decreased markers of oxidation. For example, ingestion
of HRW for 4 weeks in 16 young healthy men resulted in a 25%
increase in GSH (p< 0.003) and a 11% increase in SOD (p< 0.007)
along with an accompanying decrease in MDA levels compared
with placebo (−25.8% vs. 11.7%; p< 0.001) (Trivic et al. 2017). How-
ever, in another double-blinded, placebo-controlled, cross-over
study with 26 healthy subjects (13 females, 13 males; mean age
34.4 ± 9.9), ingestion of HRW for 4 weeks did improve mood,
reduce anxiety, and decrease sympathetic nerve activation, but it
did not significantly reduce levels of oxidative stress. However,
the levels were all within a normal healthy range (Mizuno et al.
2017). In contrast, in an 8-week study of patients with metabolic
syndrome, ingestion of HRW caused a 39% increase in SOD
(p< 0.05) and a 43% decrease in thiobarbituric acid reactive sub-
stances (Nakao et al. 2010). Comparable increases in endogenous an-
tioxidants from regular exercise have been reported in some studies
(Ortenblad et al. 1997), while other studies show no increased antioxi-
dant levels from exercise training (Tiidus et al. 1996).
H
2
may also be helpful in improving the rate of recovery in soft
tissue injuries. In a study of 36 professional athletes, hydrogen
treatment was effective in sports-related soft tissue injury by increas-
ing the rate of return-to-normal range of motion for the injured limb
(Ostojic et al. 2014). Additional randomized, placebo-controlled,
cross-over studies suggest that H
2
decreases the rate of perceived
exertion and lowers heart rate during submaximal exercise in young
healthy adults (n= 19) (LeBaron et al. 2019), as well as improves
V
˙O
2
max in mid-age overweight women (n= 12) (Ostojic et al. 2018),
and reduces exercise-induced psychometric fatigue (n= 159) (Mikami
et al. 2019). More research on the acute and chronic effects of molec-
802 Can. J. Physiol. Pharmacol. Vol. 97, 2019
Published by NRC Research Press

ular hydrogen administration and its varying methods of delivery in
exercise medicine and sports performance is needed to determine its
true efficacy, and from which types of exercises and in which popu-
lations the most benefit would occur.
Safety
One important advantage of hydrogen is its lack of toxicity,
giving it a high safety profile. Hydrogen has been used since the
1940s to prevent decompression sickness in deep-sea diving (Case
and Haldane 1941;Dougherty 1976). No toxic effects were observed
even at 98.87% H
2
and 1.13% O
2
at 19.1 atm (Friess et al. 1978).
Additionally, hydrogen gas is naturally found in our blood and
breath due to normal fermentation of nondigestible carbohy-
drates from intestinal bacteria (Strocchi and Levitt 1992). This
bacterially produced hydrogen gas has also been shown to be
therapeutic (Kajiya et al. 2009). Even though the amount of gas is
often more than what is ingested from drinking HRW, ingestion
of HRW is still effective, and at least in some cases more effective
(Ito et al. 2012). Perhaps hydrogen is mildly toxic as suggested by
its hormetic actions. Thus, the toxic effects are potent enough to
induce hormesis, yet mild enough to be obscured and essentially
be converted to beneficial effects. This hypothesis would also ex-
plain why constant exposure to molecular hydrogen provides no
biological effects (Ito et al. 2012).
Summary of hydrogen’s potential benefits
We suggest that hydrogen can benefit athletic performance
because it can (i) rapidly reach subcellular compartments via
Table 2. Selected studies on hydrogen administration on sports exercise.
Reference Type
Model
(quality*) Design
Sample
size, nPrimary outcome
Mikami et al. 2019 Aerobic, mental fatigue Humans (2) RT, DB, PC 159 Improved endurance via V
˙O
2
, and reduced
psychometric fatigue
LeBaron et al. 2019 Aerobic endurance (V
˙O
2
) Humans (3) RT, DB, PC, CO 19 Decreased exercising heart rate during
submaximal intensity
Ostojic et al. 2018 Aerobic endurance (V
˙O
2
) Humans (3) RT, DB, PC, CO 12 Improved V
˙O
2
max, increased exercise time, and
more work done
Kawamura et al. 2018 Neutrophil dynamics and
function
Humans (3) RT, DB, PC, CO 9 No statistically significant differences were
observed in function or IL-6
Shin et al. 2018 Run-induced oxidative
stress
Humans (2) RT, DB, PC, CO 15 Reduced oxidative markers (8-OHdG, MDA) and
faster return to baseline
Sha et al. 2018 Microbiome, ROS
inflammation
Humans (2) RT, DB, PC 20 Improved microbiome; decreased MDA, IL-1, IL-6,
and TNF-␣; increased SOD and TAC
Aoki et al. 2012 Muscle fatigue Humans (3) RT, DB, PC, CO 10 Reduced lactate and fatigue; no changes in d-ROMs
or BAP
Ostojic´ et al. 2011 Running performance Humans (3) RT, DB PC, CO 18 Decreased perceived exertion and lactate levels; no
change in TAC
Ostojic and Stojanovic
2014
Safety in athletes Humans (3) RT, DB, PC 52 No adverse effects from 14 days of oral ingestion of
2 L HRW per day
Ponte et al. 2017 Prolonged repetitive
sprints
Humans (2) RT, PC, SB, CO 8 Maintained peak-power output during repetitive
sprints to exhaustion
Sun and Sun 2017 Two hours of intense
swimming exercise
Humans (2) RT, PC 60 Significantly improved SOD and TAC; decreased
superoxide levels
Ostojic et al. 2014 Musculotendinous injury
in athletes
Humans (2) RT, SB 36 Decreased plasma viscosity; faster recovery from
soft tissue injury
Kawamura et al. 2016 Muscle soreness Humans (2) RT, DB, PC, CO 9 Reduced delayed onset muscle soreness; no change
in d-ROMs or BAP
Shibayama et al. 2017 Redox status in intense
exercise
Humans (2) RT, SB, PC, CO 8 Significantly suppressed the exercise-induced
reduction in BAP/d-ROMs ratio
Koyama et al. 2008 DNA damage from
exercise
Humans (1) RT, DB, PC —Suppressed urinary excretion of exercise-induced
increases of 8-OHdG
Drid et al. 2016 Judo post exercise
recovery
Humans (1) RT, DB, PC, CO 5 Decreased blood lactate and a trend for reduced
post-exercise heart rate
Drid et al. 2013 Intense judo training Humans (1) RT, SB, PC 12 Significantly reduced lactate elevation induced
after 1 h of intense judo training
Tsubone et al. 2013 Oxidative stress in
maximal exercise
Horses (2) RT, PC 5 Attenuated oxidative stress induced from maximal
exercise
Yamazaki et al. 2015 Oxidative stress in
maximal exercise
Horses (2) RT, PC 13 Significantly reduced oxidative stress immediately,
3 h, and 24 h after exercise
Wang et al. 2015 Eccentric exercise Mice (1) RT, PC 40 Significantly increased sirtuin-3 and MnSOD;
decreased NLRP3 and Il-1␤
Ara et al. 2018 Forced swim test fatigue
and stress
Mice (2) RT, PC 21 Decreased lactate, BUN, TNF-␣, IL-6, IL-17, and IL-1␤;
increased GPx
Nogueira et al. 2018 Run-induced oxidative
stress
Mice (2) RT, PC 60 Increased SOD, decreased TBARS, mildly blunted
inflammation (i.e., TNF-␣, IL-6)
Note: RT, randomized trial; DB, double-blinded; PC, placebo-controlled; CO, cross-over; SB, single-blinded. 8OHdG, 8-hydroxy-2=-deoxyguanine; BAP, biological
antioxidant potential; BUN, blood urea nitrogen; d-ROM, diacron reactive oxygen metabolite; GPx, glutathione peroxidase; HRW, hydrogen-rich water; IL, interleukin;
MDA, malondialdehyde; NLRP3, NOD-like receptor prin domain-containing 3; SOD, superoxide dismutase; TAC, total antioxidant capacity; TBARS, thiobarbituric acid
reactive substances; TNF-␣, tumor necrosis factor-␣;V
˙O
2
, oxygen consumption; V
˙O
2
max, maximal oxygen consumption.
*Quality Rating 1–3, where 1 is of the lowest quality either because it was not controlled and (or) because the details are not open to the public (e.g., non-English
language), and 3 is of the highest reliability performed in hydrogen research.
LeBaron et al. 803
Published by NRC Research Press

passive diffusion and protect DNA, RNA, proteins, cell mem-
branes, and mitochondria from damage (Ohta 2015); (ii) selectively
decrease only the most cytotoxic radicals without eliminating
beneficial signalling (Ohsawa et al. 2007); (iii) maintain redox ho-
meostasis by decreasing the oxidant load via signal modulation
(e.g., downregulation of the NADPH oxidase system) (Sato et al.
2008); (iv) activate the Nrf2 pathway with subsequent upregula-
tion of endogenous antioxidants (e.g., GSH, CAT, GPx, and induc-
tion of heme oxygenase-1) (Zhai et al. 2014); and (v) decrease
excessive levels of pro-inflammatory mediators (e.g., cytokines,
COX2, NFAT, etc.) Additionally, in some cases, molecular hydrogen
also increases oxidant production (e.g., superoxide) (Murakami et al.
2017), and so potentially provides hormetic benefits similar to those
due to exercise. Lastly, hydrogen also increases sirtuin 3 expres-
sion (Wang et al. 2015), maintains mitochondrial membrane po-
tential (Cui et al. 2014), increases ATP production (Dohi et al. 2014),
and has other benefits as shown in Table 1, all of which can pro-
vide an ergogenic and cytoprotective benefit for elite and nonelite
athletes.
Conclusion
Exercise is associated with many effects that are either noxious
or beneficial, depending on its intensity, duration, and frequency.
In either case, these effects are at least partly mediated by
exercise-induced increases in ROS and inflammation that activate
various transcription factors, leading to their phenotypic expres-
sion. Similar to prolonged high-intensity exercise, various disease
conditions are also associated with excessive ROS and inflamma-
tion. Molecular hydrogen attenuates many of these pathological
disease conditions in animal and human studies, suggesting that
it may similarly mitigate the toxic effects of chronic, high-intensity
exercise training in elite athletes, or sporadic, high-intensity exer-
cise bouts in untrained individuals. Hydrogen may play an impor-
tant role as an exercise mimetic and redox adaptogen to regulate
the exercise-induced production of inflammation, and protect
against harmful cellular stress. These biomedical properties of
hydrogen and the human studies on exercise performance sug-
gest that it has ergogenic potential worthy of further explora-
tion. However, additional human studies with different doses,
durations, and methods of administration are required before
stronger recommendations or conclusions can be made.
Acknowledgement
This study was supported by grants APVV-15-0376, VEGA 2/0021/15,
and ITMS 26230120009.
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