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Evidence-Based Complementary and Alternative Medicine
Volume 2011, Article ID 932430, 10 pages
doi:10.1093/ecam/nep169
Original Article
Diaphragmatic Breathing Reduces
Exercise-Induced Oxidative Stress
Daniele Martarelli, Mario Cocchioni, Stefania Scuri, and Pierluigi Pompei
Department of Experimental Medicine and Public Health, University of Camerino, Via Madonna delle Carceri, 62032 Camerino,
Macerata, Italy
Correspondence should be addressed to Daniele Martarelli, daniele.martarelli@unicam.it
Received 31 March 2009; Accepted 2 October 2009
Copyright © 2011 Daniele Martarelli et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Diaphragmatic breathing is relaxing and therapeutic, reduces stress, and is a fundamental procedure of Pranayama Yoga, Zen,
transcendental meditation and other meditation practices. Analysis of oxidative stress levels in people who meditate indicated that
meditation correlates with lower oxidative stress levels, lower cortisol levels and higher melatonin levels. It is known that cortisol
inhibits enzymes responsible for the antioxidant activity of cells and that melatonin is a strong antioxidant; therefore, in this study,
we investigated the effects of diaphragmatic breathing on exercise-induced oxidative stress and the putative role of cortisol and
melatonin hormones in this stress pathway. We monitored 16 athletes during an exhaustive training session. After the exercise,
athletes were divided in two equivalent groups of eight subjects. Subjects of the studied group spent 1h relaxing performing
diaphragmatic breathing and concentrating on their breath in a quiet place. The other eight subjects, representing the control
group, spent the same time sitting in an equivalent quite place. Results demonstrate that relaxation induced by diaphragmatic
breathing increases the antioxidant defense status in athletes after exhaustive exercise. These effects correlate with the concomitant
decrease in cortisol and the increase in melatonin. The consequence is a lower level of oxidative stress, which suggests that an
appropriate diaphragmatic breathing could protect athletes from long-term adverse effects of free radicals.
1. Introduction
Stress is defined as a physiological reaction to undesired emo-
tional or physical situations. Initially, stress induces an acute
response (fight or flight) that is mediated by catecholamines.
When stress becomes chronic and lasts for a long time, the
stressed organism reacts with physiological alterations to
adapt to the unfavorable conditions. This ACTH-mediated
reaction affects the immune and neuroendocrine systems,
and it is responsible for several diseases [1]. Numerous
data support the hypothesis that the pathophysiology of
chronic stress can be due, at least partially, to an increase
in oxidative stress [2–4], which may also contributes to
heart disease [5,6], rheumatoid arthritis [7,8], hypertension
[9,10], Alzheimer’s disease [11,12], Parkinson’s disease [13],
atherosclerosis [14] and, finally, aging [15].
Some authors have attributed stress-induced oxidative
stress to an increase in glucocorticoids. In fact, there is
evidence to suggest that glucocorticoids induce oxidative
stress mainly by altering the expression and activity of
antioxidant enzymes, thus impairing the antioxidant defense
of the body [16–19]. High levels of glucocorticoids are
known to decrease blood reduced glutathione (GSH) and
erythrocyte superoxide dismutase (SOD) activity in rats
[20]. Other enzymes are also involved, and NADPH oxidase,
xanthine oxidase and uncoupled endothelial nitric oxide
synthase are important sources of reactive oxygen species
(ROS) in glucocorticoid-induced oxidative stress (see [9]for
a review on this argument).
A number of studies support the fact that meditation,
through the modulation of the neuroendocrine response,
combats stress and its related diseases. In fact, beyond
its psychological and social effects, clinical studies have
documented that meditation improves the immune system
[21] and decreases cardiovascular risk factors such as
hyperlipidemia, hypertension and atherosclerosis [22–30].
A reduction in both glucocorticoids and oxidative stress
has been documented in people who practice meditation
regularly. Hormonal reactions to stressors, in particular
plasma cortisol levels, are lower in people who meditate than
2 Evidence-Based Complementary and Alternative Medicine
in people who do not [31–36], suggesting that it is possible to
modulate the neuroendocrine system through neurological
pathways. Analysis of oxidative stress levels in people who
meditate indicated that transcendental meditation, Zen
meditation and Yoga correlate with lower oxidative stress
levels [37–43].
Melatonin could also be involved in the reduction of
oxidative stress because increased levels of this hormone have
been reported after meditation [44–46]. This neurohormone
is considered a strong antioxidant and is used as a treatment
for aging. Melatonin in fact, increases several intracellular
enzymatic antioxidant enzymes, such as SOD and glu-
tathione peroxidase (GSH-Px) [47,48], and induces the
activity of γ-glutamylcysteine synthetase, thereby stimulating
the production of the intracellular antioxidant GSH [49]. A
number of studies have shown that melatonin is significantly
better than the classic antioxidants in resisting free-radical-
based molecular destruction. In these in vivo studies, mela-
tonin was more effective than vitamin E, β-carotene [50–52]
and vitamin C [53–55]. In addition to mental stress, physical
stress also increases the production of ROS. In exhaustive and
prolonged exercise, ROS production is elevated, and changes
in exercise intensity (aerobic-anaerobic) have been associated
with a higher degree of oxidative stress [56–59]. Although it
has been established that a continuous and moderate physical
activity reduces stress, intense and prolonged exercise is
deleterious and needs a proper recovery procedure. The
link between physical and psychological stress is apparent
becausetheyhaveequivalenthormonalresponses.Actually,
both types of stress are characterized by activation of the
neuroendocrine axis, which leads to the production of ACTH
and cortisol. The beneficial or detrimental role of cortisol in
athletes has been debated, as some believe that its catabolic
actions are detrimental to muscle recovery, whereas others
believe that its anti-inflammatory actions are beneficial to
muscle recovery. Plasma cortisol levels increase in response
to intense and prolonged exercise [60,61]. Ponjee et al. [62]
demonstrated that cortisol increased significantly in male
athletes after they ran a marathon. In another study, plasma
ACTH and cortisol were found elevated in highly trained
runners and in sedentary subjects after intense treadmill
exercise [63].
Additionally, melatonin levels are affected by physical
activity. There are some conflicting reports regarding the
effects of exercise on melatonin levels, with some studies
reporting an increase, some a decrease and some reporting
no change in melatonin concentrations after exercise [64–
70]. However, these contradictory results could be due to
light conditions and the timing or intensity of exercise.
Moreover, sex, age and training of the monitored athletes
may contribute to the different results reported in these
studies. It has been speculated that intense sport increases
melatonin secretion due to the necessity of combating the
free radical production that occurs during exercise, and
melatonin could be responsible for amenorrhea in female
athletes as an effect of overtraining [71].
Most, if not all, meditation procedures involve diaphrag-
matic breathing (DB), which is the act of breathing deeply
into the lungs by flexing the diaphragm rather than the rib
cage. DB is relaxing and therapeutic, reduces stress and is
a fundamental procedure of Pranayama Yoga, Zen, transcen-
dental meditation and other meditation practices.
Although exercise-induced ROS production can be pro-
duced via different pathways [56], we speculated that by
combating the exercise-induced increase in cortisol levels
and by stimulating melatonin levels, DB could improve
antioxidant defenses and, therefore, decrease oxidative stress.
We have recently demonstrated that in master athletes, oxida-
tive stress induced by intense exercise reaches dangerous
levels [72]. Therefore, in this study, we investigated the
effects of DB on exercise-induced oxidative stress and the
putative role of cortisol and melatonin hormones in this
stress pathway.
2. Methods
2.1. Subjects and Exercise. Athletes were monitored during
a training session for a 24-h long contest. This type of race
lasts for 24 h, generally starting at 10:00 am and ending at
10:00 am the following day. Bikers ride as many kilometers as
possible on a specific circuit trail in the 24-h period. Athletes
are allowed to stop, to sleep, to rest and to eat as much food
as they want to eat.
The session analyzed in this study was a reproduction of
the first 8 h of the race, which is generally the most intense.
Athletes started to ride at 10:00 am and stopped at 6:00 pm.
They consumed the same food and rested the same time.
Since the parameters measured can differ for each
individual, we performed preliminary analyses to select
subjects with comparable cortisol, melatonin, antioxidant
and oxidative stress values.
We selected 16 amateur male cyclists, aged 44.4 ±2
years (±SD). Their mean height and weight were 175.4 ±
7.5 cm and 68.8 ±5.7 kg, respectively, (Ta bl e 1 ). Subjects
were informed of the purpose of the study, and all of them
gave their informed consent prior to their inclusion. This
study has been performed in accordance with the ethical
standards laid down in the 1964 declaration of Helsinki.
None of the subjects had taken medication or supple-
ments within the past 30 days that might alter the study
outcome, and none of them had a history of medical
or surgical events that could affect the study outcome,
including cardiovascular disease or metabolic, renal, hepatic
or musculoskeletal disorders.
2.2. Experimental Procedure. After exercising, athletes took
a shower and drank water to rehydrate. They were then
divided in two equivalent groups of eight subjects (Tab l e 1).
Subjects of the studied group were previously trained to relax
by performing DB and concentrating on their breath. These
athletes spent 1 h (6:30–7:30 pm) relaxing performing DB
in a quiet place. The other eight subjects, representing the
control group, spent the same time sitting in an equivalent
quite place. The only activity allowed was reading magazines.
Lighting levels were monitored throughout the experiment
and did not exceed 15 lux, a level well below that known to
influence melatonin secretion [73,74].
Evidence-Based Complementary and Alternative Medicine 3
Tab l e 1: Characteristics of the sample studied.
Athletes DB group Control group All athletes
Age
(years)
Height
(cm)
Weight
(kg)
Kilometers
covered
Age
(years)
Height
(cm)
Weight
(kg)
Kilometers
covered
Age
(years)
Height
(cm)
Weight
(kg)
Kilometers
covered
Mean 44.50 175.25 68.63 130.13 44.38 175.50 69.13 128.63 44.44 175.38 68.88 129.38
SD 2.32 6.94 4.52 5.01 2.12 8.34 6.31 5.60 2.16 7.52 5.66 5.19
After the resting and DB periods, athletes consumed the
same food and retired for sleeping at 10:00 pm. At 11:00 pm,
all of them were sleeping.
We referred to the DB applied here as a relaxation
technique. Instead of training the athletes with some form
of meditation, we preferred DB because it is easy to
learn and to perform and because it does not require any
moral conviction that could generate psychologically adverse
reactions. However, DB associated with a focused mind (in
this case, awareness on the breath as specified in the methods
section) can be considered a form of meditation such as
focused meditation or others [75].
2.3. Oxidative Stress Determination. Oxidative stress was
measured by performing the d reactive oxygen metabolites
(d-ROMs) test [76,77], which determines the plasma ROMs
produced by ROS. The d-ROMs test is based on the concept
that plasmahydroperoxides react with the transition metal
ions liberated from the proteins in the acidic medium
and are converted to alkoxy and peroxy radicals. These
newly formed radicals are able to oxidize N,N-diethyl-para-
phenylendiamine to the corresponding radical cation, and its
concentration can be determined through spectrophotomet-
ric procedures (absorption at 505 nm). The d-ROMs test is
expressed in U CARR (Carratelli units), where 1 U CARR =
0.08 mg H2O2dl−1. Values higher than 300 U CARR indicate
oxidative stress. ROMs were determined before starting the
exercise (9:30 am), at the end of the exercise (6:00 pm),
immediately after the DB periods (7:30 pm), at 2:00 am, and
24 h after the exercise (10:00 am of the following day).
2.4. Biological Antioxidant Potential Determination. The
antioxidant defense status was assessed by determining the
biological antioxidant potential (BAP test), which depends
on the plasma levels of antioxidants. The BAP test is
based on the ability of a coloured solution, containing a
source of ferric (Fe3+) ions adequately bound to a special
chromogenic substrate, to lose colour when Fe3+ ions
are reduced to ferrous ions (Fe2+),whichoccurswhena
reducing/antioxidant system is added. The ferric chloride
reagent (50 μL) is transferred into a cuvette containing
the thiocyanate derivative reagent. The resulting colored
solution is gently mixed by inversion and its absorbance is
measured at 550 nm. Then, 10 μL of plasma is added to the
same cuvette, the solution is gently mixed, incubated in a
thermostatic block for 5 min at 37◦C, and its absorbance
at 550 nm is remeasured [78,79]. The BAP test results
are expressed in μmoL Fe2+/liter of sample. Values higher
than 2200 μmolLFe2+ /liter are considered a normal BAP. d-
ROMs and BAP tests were performed using apposite kits and
dedicated instrumentation Free Radical Analytical System 4
(FRAS4, Health & Diagnostics Limited Co., Parma, Italy).
Since the BAP test must be performed at least 3 h after
food was last consumed, the BAP was determined before
breakfast at 8:00 am, during the night at 2:00 am, and 24 h
post-exercise (8:00 am).
2.5. Saliva Collection. The subjects abstained from alcoholic
and caffeinated beverages from the beginning of the training
session and were only allowed to drink water. Subjects
washed their mouths with distilled water before salivary
samples were obtained using the B¨
uhlmann saliva collection
device (B¨
uhlmann Laboratories AG, Switzerland). Imme-
diately after collection, the saliva samples were frozen and
stored at –80◦C until they were assayed for cortisol and
melatonin concentrations.
2.6. Cortisol Assay. Salivary cortisol was determined before
the exercise began (10:00 am), at the end of the exercise
(6:00 pm), immediately after the DB period (7:30 pm), at
2:00 am, and 24 h after the exercise (10:00 am of the next day)
using a commercially available EIA kit (Cortisol Express,
Cayman Chemical Ann Arbor, MI, USA). Absorbance values
were determined at 415 nm using a plate reader. Samples
were assayed in triplicate.
2.7. Melatonin Assay. Salivary nocturnal melatonin was
determined at 2:00 am using the B¨
uhlmann Direct Saliva
Melatonin Elisa (B¨
uhlmann Laboratories AG, Switzerland).
This assay is based on a melatonin biotin conjugate antibody,
streptavidin conjugated to horseradish peroxidase and a
tetramethyl benzidine (TMB) substrate. The product of the
substrate was measured spectrophotometrically at 450 nm.
The assay sensitivity range was 1–60.6 pg ml−1.
2.8. Statistical Analysis. The characteristics of the studied
sample and the effects of DB were analyzed by two-way
ANOVA with repeated measurements. A two-sided t-test
(post-hoc comparisons) and the non parametric Wilcoxon-
Mann-Whitney test were used for the comparison of
numerical data across groups for each time point. A P-
value <.05 was considered statistically significant. Statistics
were compiled using Microsoft Excel and Winstat software.
Changes in melatonin levels were analyzed by the two-sided
t-test and the non-parametric Wilcoxon-Mann-Whitney
test.
4 Evidence-Based Complementary and Alternative Medicine
500
450
400
350
300
250
200
150
100
50
0
Control group
DB group
Pre-exercise
(9:30 am)
End exercise
(6:00 pm)
∗∗
∗∗
Post-
relaxation
(7:30 pm)
Night
(2:00 am)
24 h post-
exercise
(9:30 am)
ROMs levels (U CARR)
Figure 1: ROMs levels were determined at different times, before
and after exercise. Athletes were divided in two equivalent groups
of eight subjects. Subjects of the studied group spent 1 h (6:30–
7:30 pm) relaxing performing DB and concentrating on their breath
in a quiet place. The other eight subjects, representing the control
group, spent the same time sitting in an equivalent quite place.
Values shown are mean ±SD. ∗∗P<.01 DB versus control group.
3. Results
3.1. Characteristics of the Studied Sample. Subjects were
divided into two similar groups, as shown in Tabl e 1 .There
were no statistical differences for age, height, weight, or km
covered between the groups [F(1,62) =0.023; P>.5].
3.2. Oxidative Stress Changes. As expected, the exercise
induced a strong oxidative stress in athletes (Figure 1).
The ROMs levels were significantly increased after exer-
cise compared to pre-exercise levels. All athletes had an
elevation in ROMs in response to the training exercise,
reaching particularly high levels of oxidative stress. The
overall ANOVA revealed a significant DB effect [F(1,78) =
11.184; P<.01] and time effect [F(4,75) =130.481; P<.01].
After completing the training exercise, there was a significant
amount of variability between the ROMs levels of individual
athletes, suggesting that each athlete has an individual
response to oxidative stress. However, post-hoc comparisons
confirmed that the mean level of ROMs in athletes of the
DB group was significantly lower than the control-group
athletes both at 2:00 am (P<.01 DB versus control group)
and 24 h post-exercise (P<.01 DB versus control group).
For the DB group, the increase in ROMs levels post-exercise
compared to pre-exercise levels was 161.7% at 6:00 pm,
150.9% at 7:30 pm, 141.6% at 2:00 am and 126.8% 24h post-
exercise. For the control group, the increase in ROMs levels
post-exercise compared to pre-exercise levels was 160.9% at
6:00 pm, 157.1% at 7:30 pm, 159.9% at 2:00 am and 154%
24 h post-exercise.
3.3. Biological Antioxidant Potential Changes. Figure 2 shows
the BAP which significantly increased in both groups.
3000
2500
2000
1500
1000
500
0
Control group
DB group
Pre-exercise
(8:00 am)
Night
(2:00 am)
∗∗
∗
24 h post-exercise
(8:00 am)
BAPlevels(µmoL Fe2+ /liter)
Figure 2: BAP levels were determined at different times, before
and after exercise. Athletes were divided in two equivalent groups
of eight subjects. Subjects of the studied group spent 1 h relaxing
performing DB and concentrating on their breath in a quiet place.
The other eight subjects, representing the control group, spent the
same time sitting in an equivalent quite place. Since this test must
be performed several hours after food ingestion, BAP levels were
determined pre-exercise at 8:00 am before breakfast, at 2:00 am, and
at 8:00 am 24 h post-exercise. Values shown are mean ±SD. ∗P<.05
DB versus control group. ∗∗P<.01 DB versus control group.
Again, a significant variation among the subjects was
observed, but athletes of the DB group presented BAP levels
significantly higher than the control group [F(1,46) =21.001;
P<.01]. This difference was more evident at 2:00 am (P
<.01 DB versus control group, post-hoc comparisons) than
24 h post-exercise (P<.05 DB versus control group, post-
hoc comparisons), where BAP began to return to basal levels.
With respect to the pre-exercise values, for the DB group, the
increase in BAP levels was 129.1% at 2:00 am and 111.1% at
24 h post-exercise.
For the control group, the increase was 114.2% at 2:00 am
and 106.2% at 24 h post-exercise with respect to the pre-
exercise values. ANOVA also revealed a significant time effect
[F(2,45) =91.587; P<.01].
3.4. Changes in Cortisol Levels. ANOVA revealed a significant
DB effect [F(1,78) =4.028; P<.05]. As shown in Figure 3,
significant differences between the groups were observed
only at 7:30 pm, after the DB (P<.05 DB versus control
group, post-hoc comparisons). At 2:00 am and 24 h post-
exercise, cortisol levels were lower in athletes of the DB
group, but differences were not statistically significant. In
athletes of the DB group, the decrease in cortisol levels
(07:30 p.m.) temporarily precedes the decrease in ROMs
levels (2:00 am). It was not possible to determine the effects
of exercise on cortisol levels, as hormone concentrations were
determined at different times during its circadian rhythm.
With respect to the pre-exercise values, for the DB group,
cortisol values were 82.2% by 06:00 pm, 61.1% by 7:30 pm,
Evidence-Based Complementary and Alternative Medicine 5
Salivary cortisol (ng/mL)
12
10
8
6
4
2
0
Control group
DB group
Pre-exercise
(9:30 am)
End exercise
(6:00 pm)
∗
Post-
relaxation
(7:30 pm)
Night
(2:00 am)
24 h post-
exercise
(9:30 am)
Figure 3: Salivary cortisol levels were determined at different times,
before and after exercise. Athletes were divided in two equivalent
groups of eight subjects. Subjects of the studied group spent 1 h
(6:30–7:30 pm) relaxing performing DB and concentrating on their
breath in a quiet place. The other eight subjects, representing the
control group, spent the same time sitting in an equivalent quite
place. Values shown are mean ±SD. ∗P<.05 DB versus control
group.
47.7% by 02:00 am and 74.7% 24 h post-exercise. For the
control group, with respect to the pre-exercise values, values
were 83.4% by 06:00 pm, 79.1% by 7:30 pm, 54.6% by
02:00 am and 86.9% 24 h post-exercise respect to the pre-
exercise values. ANOVA also revealed a significant time effect
[F(4,75) =17.459; P<.01].
3.5. Changes in Melatonin Levels. Figure 4 shows the differ-
ences in nocturnal melatonin levels between the two groups
of athletes. Melatonin levels were significantly higher in
athletes of the DB group (P<.05 DB versus control group).
These data are congruent with the lower ROMs levels, with
the higher BAP levels and with the lower cortisol levels at
7:30 pm.
4. Discussion
This study demonstrates that DB reduces the oxidative stress
induced by exhaustive exercise. To our knowledge, this is the
first study which explores the effect of DB on the stress caused
by exhaustive physical activity.
It is known that cortisol inhibits enzymes responsible
for the antioxidant activity of cells and that melatonin is a
strong antioxidant. After the training exercise, athletes who
underwent DB presented higher levels of BAP, which are
congruous with the reduced levels of cortisol and ROMs and
with the increased levels of nocturnal melatonin. As in our
previous study [72], after exercise, we found an increase in
BAP levels in both of the groups analyzed. However, the
elevated levels of plasma antioxidant markers after exercise
can be explained considering three processes: (i) the suspen-
sion of exercise decreases oxidant production, so antioxidant
∗
Night (2:00 am)
35
30
25
20
15
10
5
0
Salivary melatonin (pg/mL)
Control group
DB group
Figure 4: Salivary nocturnal melatonin levels variation after
exercise. Values shown are mean ±SD. ∗P<.05 DB versus control
group.
defense can return to normal levels; (ii) up-regulation of
antioxidants and (iii) the mobilization of antioxidants from
tissues to blood [80]. Beyond these mechanisms, these results
also suggest that cortisol and melatonin levels could affect
the modulation of antioxidant defenses and are relevant in
determining the final level of oxidative stress. The decrease
of ROS concentrations in subjects performing DB could be
attributed to the reduced neuroendocrine response induced
by relaxation.
The rationale is as follows (Figure 5):
(i) intense exercise increases cortisol production;
(ii) a high plasmatic level of cortisol decreases body
antioxidant defenses;
(iii) a high plasmatic level of cortisol correlates with a
high level of oxidative stress;
(iv) DB reduces the production of cortisol;
(v) DB increases melatonin levels;
(vi) melatonin is a strong antioxidant;
(vii) DB increases the BAP and
(viii) DB reduces oxidative stress.
If these results are confirmed in other intense physical
activity programs, relaxation could be considered an effective
practice to significantly contrast the free radical-mediated
oxidative damage induced by intense exercise. Therefore,
similar to the way that antioxidant supplementation has
been integrated into athletic training programs, DB or other
meditation techniques should be integrated into many sports
as a method to improve performance and to accelerate recov-
ery. However, wider health implications can be accounted
for the use of DB, as it can find applications in several
pathologies. For example, the oxidative stress that occurs
in the hyperventilation syndrome can be cured by learning
6 Evidence-Based Complementary and Alternative Medicine
Exercise Diaphragmatic
breathing
Cortisol
Cortisol
Melatonin Melatonin
Antioxidant
enzymes
Free radicals
(oxidative
stress)
Antioxidant
enzymes
Free radicals
(oxidative
stress)
?
Figure 5: Modulation of oxidative stress by exercise and DB.
DB. Hyperventilation, in fact, induces hyperoxia which is
known to be related with oxidative stress [81,82]. The
hyperventilation syndrome affects 15% of the population
and occurs when breathing rates elevate to 21–23 bpm as
a result of constricted non-DB. DB can treat hyperoxia
and its consequences acting by two synergic ways: restoring
the normal breath rhythm and reducing oxidative stress
mainly through the increase in melatonin production which
is known for its ability to reduce oxidative stress induced
by exposure to hyperbaric hyperoxia [83]. Moreover, Orme-
Johnson observed greatly reduced pathology levels in regular
meditation practitioners [84,85]. A 5 years statistic of
approximately 2000 regular participants demonstrated that
Transcendental Meditation reduced benign and malignant
tumors, heart disease, infectious diseases, mental disorders
and diseases of the nervous system. Mourya et al. evidenced
that slow-breathing exercises may influence autonomic func-
tions reducing blood pressure in patients with essential
hypertension [86]. Finally, there are also evidences that
procedures which involve the control of the breathing can
positively affect type 2 Diabetes [87], depression, pain [88],
high glucose level and high cholesterol [89].
Our results contribute to explain these effects as oxidative
stress may also play a role in the development of these
pathologies [2–15]. The role of melatonin must also be
emphasized. Beyond its antioxidant properties, melatonin
is involved in the regulation of the circadian sleep-wake
rhythm and in the modulation of hormones and the
immune system. Due to its wide medical implications, the
increase in melatonin levels induced by DB suggests that this
breath procedure deserves to be included in public health
improvement programs.
In this work, we explored the acute effects of DB, but
these outcomes should also be investigated for longer peri-
ods, for which we would expect a more intense and beneficial
response. For example, it is likely that expert practitioners
who frequently utilize of DB could obtain a more significant
reduction in oxidative stress and, perhaps, an improvement
in exercise performance. Moreover, relaxation could also
be improved by adding another relaxation method to the
formula, for example music. In fact, Khalfa et al. [90]
demonstrated that relaxing music facilitates recovery from a
psychologically stressful task, decreasing the salivary cortisol.
Our results must also be discussed in light of the fact
that cortisol has an ACTH-dependent circadian rhythm with
peak levels in the early morning and a nadir at night.
Athletes start to ride at 10:00 am and stop at 6:00 pm. The
DB session started at 6:30 pm and stopped at 7:30 pm. It
is probable that these results would be different if the time
of physical activity and the DB session were changed. The
same is true for melatonin. In fact, significant differences
have been reported in melatonin secretion when exercises
were performed at different times and under different light
conditions [64–70]. We collected the saliva at 2:00 am, when
a peak in melatonin must be expected. DB increased the
levels of melatonin in athletes, and this correlates with lower
oxidative stress (ROMs), with lower cortisol levels and with
the higher antioxidant status (BAP) in these athletes.
The mechanism by which relaxation might induce an
increase in melatonin levels is uncertain, and whether the
melatonin increase is simply due to the cortisol decrease
remains to be elucidated. Different mechanisms could be
involved. Tooley et al. [46] speculated that meditation-
reduced hepatic blood flow [91] could raise the plasma
levels of melatonin. Alternatively, since meditation increases
plasma levels of noradrenaline [92] and urine levels of the
metabolite 5HIAA [93], a possible direct action on the pineal
gland could be hypothesized, as melatonin is synthesized in
the pineal by serotonin under a noradrenaline stimulus [94].
More likely, we suspect that the increase in melatonin levels
determined in our experiment can be mainly attributed to
the reduced cortisol levels. Actually, a relationship between
cortisol and melatonin rhythms has been observed [95],
indicating that melatonin onset typically occurs during low
cortisol secretion. In addition, Monteleone et al. [96]found
that exercise-induced increases in plasma cortisol preceded
Evidence-Based Complementary and Alternative Medicine 7
the lower night-time melatonin secretion, thus suggest-
ing a connection between the metabolisms of these two
hormones.
More studies are needed to clarify the link between
cortisol and melatonin; however, due to the complexity
of the pathways involved in maintaining homeostasis and
in initiating the stress response, it is plausible that the
relationship between the two hormones could be mediated
by several mechanisms.
Overall, these data demonstrate that relaxation induced
by DB increases the antioxidant defense status in athletes
after exhaustive exercise. These effects correlate with the con-
comitant decrease in cortisol, which is known to negatively
affect antioxidant defenses, and the increase in melatonin,
a strong antioxidant. The consequence is a lower level of
oxidative stress, which suggests that an appropriate recovery
could protect athletes from long-term adverse effects of free
radicals.
Funding
Department of Experimental Medicine and Public Health,
University of Camerino, Macerata, Italy.
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