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ORIGINAL CONTRIBUTION
Effect of tart cherry juice (Prunus cerasus) on melatonin levels
and enhanced sleep quality
Glyn Howatson
•
Phillip G. Bell
•
Jamie Tallent
•
Benita Middleton
•
Malachy P. McHugh
•
Jason Ellis
Received: 7 July 2011 / Accepted: 10 October 2011
Ó Springer-Verlag 2011
Abstract
Background Tart Montmorency cherries have been
reported to contain high levels of phytochemicals including
melatonin, a molecule critical in regulating the sleep-wake
cycle in humans.
Purpose The aim of our investigation was to ascertain
whether ingestion of a tart cherry juice concentrate would
increase the urinary melatonin levels in healthy adults and
improve sleep quality.
Methods In a randomised, double-blind, placebo-con-
trolled, crossover design, 20 volunteers consumed either a
placebo or tart cherry juice concentrate for 7 days. Measures
of sleep quality recorded by actigraphy and subjective sleep
questionnaires were completed. Sequential urine samples
over 48 h were collected and urinary 6-sulfatoxymelatonin
(major metabolite of melatonin) determined; cosinor anal-
ysis was used to determine melatonin circadian rhythm
(mesor, acrophase and amplitude). In addition, total urinary
melatonin content was determined over the sampled period.
Trial differences were determined using a repeated measures
ANOVA.
Results Total melatonin content was significantly ele-
vated (P \ 0.05) in the cherry juice group, whilst no dif-
ferences were shown between baseline and placebo trials.
There were significant increases in time in bed, total sleep
time and sleep efficiency total (P \ 0.05) with cherry juice
supplementation. Although there was no difference in
timing of the melatonin circardian rhythm, there was a
trend to a higher mesor and amplitude.
Conclusions These data suggest that consumption of a
tart cherry juice concentrate provides an increase in
exogenous melatonin that is beneficial in improving sleep
duration and quality in healthy men and women and might
be of benefit in managing disturbed sleep.
Keywords Tart cherries Melatonin Sleep Recovery
Introduction
Tart Montmorency cherries (Prunus cerasus), rich in
numerous phytochemicals, provide a range of health benefits
that include reduction in symptoms associated with gout [1],
down-regulation of circulating inflammatory markers [2],
analgesic effects following long-distance running [3],
reduced oxidative stress [4], improved recovery following
damaging exercise [5–7] and recently, improved sleep
quality in late-life insomnia [8]. Mechanistically, it is
thought the phenolic compounds within tart cherries act as
‘free radical’ scavengers that reduce oxidative stress [2]. In
addition, the anti-inflammatory properties [9] of tart cherries
have been reported to be at a level comparable to a number of
non-steroidal anti-inflammatory drugs [10]. In particular, the
anthocyanin content of tart cherries, which compares
G. Howatson (&) P. G. Bell J. Tallent J. Ellis
School of Life Sciences, Northumbria University,
Northumberland Building, Newcastle upon Tyne NE1 8ST, UK
e-mail: glyn.howatson@northumbria.ac.uk
G. Howatson
Centre for Aquatic Research, Department of Zoology,
University of Johannesburg, Johannesburg, South Africa
B. Middleton
Centre for Chronobiology, Faculty of Health and Medical
Sciences, University of Surrey, Guildford, UK
M. P. McHugh
Nicholas Institute of Sports Medicine and Athletic Trauma,
Lenox Hill Hospital, New York, NY, USA
123
Eur J Nutr
DOI 10.1007/s00394-011-0263-7
favourably with other fruits such as sweet cherries [11],
seems to be of most interest, and these are likely to be
responsible for the anti-oxidative and anti-inflammatory
effects.
A number of recent studies have shown that consump-
tion of tart cherry juice can accelerate recovery following
strenuous exercise [5–7], where temporary perturbations in
inflammation and oxidative stress can occur. These
recovery effects have been attributed to the actions of the
antioxidant and anti-inflammatory phytochemicals con-
tained in tart cherries. Pigeon et al. [8] anecdotally reported
claims of improved sleep with cherry juice supplementa-
tion in participants from a previous trial [6]. Interestingly,
in addition to the aforementioned phenolic compounds, tart
cherries contain high concentrations of melatonin [12].
Melatonin has a strong influence on the sleep-wake cycle in
humans and is associated with sleep-promoting properties
[13]. Physiologically, endogenous melatonin secretion
adjusts according to the light/dark cycle and can directly
influence nocturnal core temperature and hence facilitate
the propensity for sleep [14]. Additionally, a strong posi-
tive relationship between increased melatonin and total
sleep time in healthy, young individuals has been previ-
ously demonstrated [15]. Interestingly, the balance of evi-
dence would suggest that exogenous melatonin in the
treatment of insomnia is equivocal at best; however, there
is a good body of support for melatonin use in managing
circadian rhythm disturbance, such as those seen from
travelling time zones [16].
In a recent study, the efficacy of tart cherry juice con-
sumption on sleep indices in a population with late-life
insomnia was examined [8]. They reported modest
improvements in subjective quality of sleep; however, no
objective measures of sleep, such as actigraphy, were
taken, and the potential mechanisms responsible for the
reported sleep improvements (e.g. melatonin) were
impossible to discern. The authors [8] speculated that
increased dietary melatonin associated with consumption
of tart cherry juice might be responsible for the changes.
However, there is an alternative hypothesis; the anti-
inflammatory properties of tart cherries may have some
influence on the pro-inflammatory cytokines involved in
sleep regulation [17]. Given the potential benefits of tart
cherry juice in delivering exogenous melatonin and
improving sleep quality, we hypothesised that the con-
sumption of a tart cherry juice concentrate in young,
healthy adults would increase urinary 6-sulfatoxymelatonin
and improve indices of sleep quality. Therefore, the aim
of this investigation was to examine the effects of
tart Montmorency cherry juice concentrate on urinary
6-sulfatoxymelatonin and sleep quality using a double-
blind, placebo-controlled, crossover design.
Methods
Participants
Following institutional ethical approval from the School of
Life Sciences Ethics Committee at Northumbria Univer-
sity, UK in accordance with the Helsinki Declaration, 20
healthy men (n = 10) and women (n = 10) volunteered to
participate. The mean (±SD) age, height, body mass and
BMI were 26.6 (±4.6) years, 1.71 (±0.10) m, 72.5 (±15.0)
kg and 24.7 (±3.5) kg m
-2
, respectively. The age range
was restricted to 18–40 years to reduce the potential for
age-related sleep disturbances that have been reported in
older adults [13]. In addition, all volunteers were physi-
cally active and participated in moderate physical exercise
for at least 150 min/week. After being informed of the
experimental procedures, participants were asked to com-
plete a health screening questionnaire to ascertain contra-
indications to participation (prescription medicines, sleep
disturbance, special dietary habits, shift work or underlying
medical pathology), and volunteers then provided written
informed consent.
Experimental overview and study design
Participants were supplemented with a tart cherry juice
concentrate or placebo in a randomised, double-blind,
placebo-controlled, crossover study design, during normal
daily routine. Dependent variables were urinary 6-sul-
phatoxymelatonin (aMT6s), diet recall, objective activity
recorded through actigraphy (variables) and subjective
sleep quality. A schematic of the study design is presented
in Fig. 1. Initially, participants provided sequential urinary
voids across a 48 h period (days 1 and 2) in order to ana-
lyse baseline measures of aMT6s. Over the same 2-day
period, participants were issued with an activity monitor
and completed online daily diet recalls and a sleep diary
immediately following morning awakening. Participants
then continued to complete the questionnaires and diaries
and wear the activity monitors for the remainder of the trial
period.
Following the 48-h baseline period, participants were
randomly assigned to either the tart cherry juice concen-
trate or placebo (starting on day 3) for a period of 7 days;
this was based on loading phases from previous studies
showing efficacy using cherry juice [5–8]. Participants
were instructed to consume two servings of either tart
cherry juice concentrate or fruit-flavoured cordial each day,
for 7 days. In the last 48 h of this supplementation period,
urine was again collected in an identical manner as pre-
viously described for the baseline period. Following a
14-day washout period, participants repeated the baseline
Eur J Nutr
123
and experimental period whilst consuming the other
supplement.
Dietary control
All volunteers completed a dietary recall throughout the
baseline and supplementation periods. Participants were
asked to replicate their diet during the first supplementation
period as closely as possible during the second period in
order to standardise the dietary intake between trials.
Additionally, in order to isolate dietary melatonin as clo-
sely as possible, participants were issued with a list of
foods that are known to contain or influence melatonin and
were subsequently asked to abstain from consuming these
for the duration of the trial. Portions of foods thought to
contain antioxidants were totalled for each day then aver-
aged across the experimental period.
Supplementation
Prior to starting the experiment, participants were informed
that the trial was to ascertain the influence of two fruit con-
centrates on melatonin levels and sleep quality; however, the
nature of the trial regarding tart cherry juice concentrate was
only revealed when the study had been completed. A serving
of 30 mL of tart Montmorency cherry juice (Prunus cerasus)
concentrate (Cherry Active, Sunbury, UK) was consumed
within 30 min of wakening and 30 min before the evening
meal on each of the 7-day supplementation periods. Each
30 mL serving was estimated to contain the equivalent of
approximately 90–100 tart cherries and was diluted with
approximately 200 mL of water. An independent laboratory
(Atlas Bioscience Inc., Tuscan, AZ) conducted melatonin
analysis of the cherry juice concentrate adapting an estab-
lished HPLC method [18]. The concentration of melato-
nin was 1.42 lgmL
-1
, which equates to a dose of
*42.6 lg/30 mL serving or *85.2 lg day
-1
. Literature
suggests that daily melatonin doses of *0.5–5 mg confer a
positive effect in managing disturbed sleep rhythm [19].
In addition, other active compounds contained within the tart
cherry juice were verified by the aforementioned laboratory
and included anthocyanins such as malvidin, cyanidin, pe-
largonidin, peonidin, delphinidin, petunidin (total anthocy-
anin content = 9.117 mg mL
-1
), vitamin A—as beta-
carotene (22.64 IU mL
-1
) and vitamin C—ascorbic acid
(0.324 mg mL
-1
).
The placebo was a commercially available, economy,
mixed fruit cordial (containing less than 5% fruit) that was
reported to contain no melatonin or anthocyanins and a
trace of vitamin C. Participants were instructed to take the
same dose (30 mL) diluted with *200 mL of water.
Dependent variables
Urine collection and analysis
Sequential urinary voids were collected 48-h periods to
ensure the entire circadian cycle was captured during
each part of the trial to allow for cosinor analysis that
provided measures of acrophase, mesor and amplitude.
Urine was collected in a sterilised measuring cylinder.
Void volume, time and date were recorded, before a
10 mL aliquot of urine was retained, refrigerated and
returned to the laboratory the following morning for
labelling and immediate storage at -80 °C for later anal-
ysis for urinary aMT6s.
Urinary 6-sulphatoxymelatonin, aMT6s
Urinary 6-sulphatoxymelatonin, aMT6s (the major metab-
olite of melatonin) was analysed in duplicate using a
radioimmunoassay [20]. Samples belonging to the same
participant were measured in the same assay run; the intra-
assay coefficient of variation was \8%; the limit of
detection was 0.25 ng mL
-1
. Evaluation of aMT6s profiles
was performed using cosinor analysis, based upon the least
square approximation of the time series using a cosine
function with a period of 24 h [21]. Parameters obtained
Fig. 1 A schematic outlining
the implemented protocol.
Supplementation periods
consisted of two 30-mL
servings per day of either a tart
cherry juice concentrate of
placebo
Eur J Nutr
123
from this analysis included the following: acrophase time:
the time of peak aMT6s concentration or the maximum of
the fitted cosinor function; mesor: the mean aMT6s values
for all samples included in the cosinor anlaysis; and
amplitude: the difference between mesor and peak aMT6
concentrations. Acrophase time was classed as normal if it
occurred between midnight and 06:00 h [22]. ‘Goodness of
fit’ measures were used to determine the validity of the
cosinor-derived indices: (1) the % rhythm or variability
accounted for by the cosine curve: 100% rhythm = all data
points fall on the cosine curve and 0% rhythm = none of
the data points fall on the cosine curve and (2) the likeli-
hood of data points fitting a straight line as opposed to a
cosine curve, expressed as a P value. Data were considered
acceptable if the cosinor fit was significant (P B 0.05) and
the % rhythm C50% [21]. Finally, the total aMT6s
excreted per 24 h was calculated and a mean for each 48-h
collection period determined.
Actigraphy
Polysomnography (PSG) offers the most accurate assess-
ment of sleep and sleep quality; however, given the nature
of the study, we utilised actigraphy that has been shown to
be reliable and has good agreement with PSG [23]. Par-
ticipants were issued with actigraphy that was worn on the
wrist of the non-dominant arm (Actiwatch 7, CamnTech,
Cambridge, UK). These were worn for the duration of the
study and removed only for bathing, showering or other
aquatic activities. Participants were asked to activate the
marker function on the watch when getting into bed and
when rising the following morning. Analysis was made on
sleep efficiency (SE), sleep onset latency (SOL), time in
bed (TIB), fragmentation index (FRAGI), total sleep time
(TST) and sleep efficiency total (SET); these variables
were calculated using Actiwatch software (Actiwatch,
CamnTech, Cambridge, UK). The mean values for each
sample period were used for data analysis.
Subjective measures
Online subjective sleep diaries were reported immediately
following awakening each day during both baseline and
trial periods. This commonly used self-reporting method
tool has been to be a reliable (90%) measure [24] and
allowed calculation of the following: SE, SOL, wake after
sleep onset (WASO), napping (NAP), TST and SET [25].
Statistical analyses
Values are reported as mean (±SD), unless otherwise sta-
ted. The cosinor data, total aMT6s and all quantitative
(actigraphy)- and qualitative (questionnaire)-dependent
sleep variables were analysed with a repeated measures
ANOVA (condition, placebo vs. cherry juice 2; time, pre
vs. post). In addition, 95% confidence intervals were also
determined to illustrate the magnitude of change. Finally,
baseline measures were examined for differences using a
paired samples t test. Significance was set at an alpha level
of 0.05.
Results
Baseline measures taken before the placebo and cherry
juice trials were not different for any of the dependent
variables (P [ 0.05). All variables returned an observed
power value ranging from 0.156 to 0.999. Although we
did not quantify all the food consumption using dietary
analysis, participants reported a similar diet across the
trials. In an attempt to quantify this more fully, we
recorded the number of food portions thought to contain
antioxidants (including melatonin) across the supplemen-
tation periods, 22.8 versus 22.4 for the cherry juice and
placebo groups, respectively. A paired samples t test
showed no significant differences between groups
(t = 1.162, P = 0.259).
Urinary 6-sulphatoxymelatonin (aMT6s)
The baseline measures preceding the placebo and cherry
juice supplements were not different (t
= 0.921,
P = 0.369). The repeated measures ANOVA showed a
significant trial effect (F = 23.0, P \ 0.001). A significant
interaction (F = 23.0, P \ 0.001) was also found and
post hoc analysis revealed that the cherry juice trial was
significantly greater than baseline and placebo trials
(P \0.001; 95% CI = 2,828–5,393 ng and 2,519–5,450 ng,
respectively); there was no difference between baseline or
placebo groups (Fig. 2).
Despite the significant increase in total urinary aMT6 s,
the cosinor analysis examining circadian rhythm of aMT6s
showed no differences between trials for any variable
(Table 1). Cosinor analysis relies on a significant ‘fit’ of
the melatonin response; of the 80 sets of data collected,
22.5% (n = 18) were excluded because they did not sig-
nificantly fit according to the cosinor algorithm. Of the
remaining data, there were small non-significant rises in the
amplitude and mesor in the cherry juice trial, whilst the
acrophase remained largely unchanged throughout. A
representative example where urinary voids were collected
for a single participant at similar times of the day between
the placebo and cherry juice trials is presented in Fig. 3;
these data span the circadian changes in aMT6s over
sequential 48-h periods.
Eur J Nutr
123
Sleep indices: subjective questionnaire and actigraphy
There was a 100% completion rate for the sleep ques-
tionnaires. There was no differences across the different
trials for SET, SOL, TST and WASO; however, napping
time did show a significant trial and interaction effect
(F = 5.591, P = 0.029), with significantly less napping
time in the cherry juice trial compared to baseline and
the placebo trials (P B 0.031; 95% CI = 0.7–13.6 and
0.7–11.1 min, respectively), and there were no differences
between baseline measures and the placebo trial (Table 2).
Whilst all participants wore the activity monitor for the
duration of the trials, 17 out of 80 trials (21.3%) were
excluded from analysis due to missing data. There were no
differences in SOL and FRAGI; however, there was a sig-
nificant trial and interaction effect for TIB (F = 7.056,
P = 0.016) where cherry juice significantly increased time
in bed compared to both baseline and placebo trails
(P B 0.017; 95% CI = 4.5–45.2 and 4.7–40.2 min,
respectively). Furthermore, TST showed a trial and inter-
action effect (F = 11.189, P = 0.003), where the cherry
juice trial was significantly greater TST than baseline and
placebo trials (P B 0.003; 95% CI = 15.2–39.7, 14.7–63.6,
respectively). In addition, SET showed significant trial and
interaction effects (F = 5.410, P = 0.031), where the
cherry juice trial was greater than the baseline and placebo
trials (P B 0.017; 95% CI = 2.1–7.5 and 0.5–9.4, respec-
tively). A summary of these data is presented in Table 3.
Discussion
The aim of this investigation was to ascertain whether the
supplementation of tart Montmorency cherry juice con-
centrate would (1) increase the urinary aMT6s content
and (2) improve the objective and subjective sleep indices
of young, healthy individuals. We hypothesised that
urinary aMT6s would rise and that sleep parameters
would improve as a consequence. This is the first inves-
tigation to demonstrate that dietary tart cherry juice
concentrate increases urinary melatonin levels and pro-
vides improved sleep time and quality in a healthy adult
population.
The sleep diary information showed that napping time
decreased with the administration of cherry juice, whereas
the actigraphy showed an increase in TIB, TST and SET, a
global measure of sleep quality. Notwithstanding the rel-
atively low baseline SET observed from the actigraphy in
these apparently good sleepers, the cherry juice nonetheless
showed a 5–6% increase in SET, which likely to be
influenced by the significant increase in TST. In addition,
given that napping decreased and total time in bed also
increased during the cherry juice trial, this is perhaps
unsurprising. What is also interesting to note is that there
Fig. 2 Mean (±SEE) urinary melatonin (aMT6) secretion for the
group following baseline placebo (control), placebo, baseline cherry
juice (control) and cherry juice trials.Asterisk denotes that cherry
juice supplementation resulted in significantly greater aMT6s than
baseline and placebo trials (P B 0.05)
Table 1 Mean (±SD) cosinor analysis based on melatonin circadian rhythm for all experimental conditions
Baseline placebo Placebo Baseline cherry juice Cherry juice
Mesor (ng 9 h
-1
) 17.98 (6.04) 19.17 (7.37) 18.64 (9.76) 21.59 (6.85)
Amplitude (lg 9 h
-1
) 27.39 (15.78) 27.54 (8.37) 27.05 (10.72) 28.57 (15.01)
Acrophase (time) 4.03 (1.03) 3.55 (1.22) 4.05 (1.40) 4.01 (1.01)
Of the possible 80 data sets, 18 did not significantly fit the cosinor curve and were excluded from the analysis
Fig. 3 A representative example of a single subject’s circadian
rhythm for urinary melatonin (aMT6s) during the placebo and cherry
juice trials over sequential 48-h periods
Eur J Nutr
123
were non-significant trends towards decreased SOL, which
is also likely to have influenced the SET.
Only one study has investigated tart Montmorency
cherry juice and sleep parameters (a fresh pressed cherry
juice blended with apple juice, as opposed to a pure cherry
juice concentrate) [8]. They found that elderly individuals,
with moderate/severe insomnia, reported improved sleep
quality, and it was hypothesised that this was due to the
increased exogenous melatonin content afforded by the
cherry juice. Unfortunately, they did not measure melato-
nin; however, data from our investigation lend additional
evidence that improved sleep quality is mediated by the
increase in dietary melatonin contained within the cher-
ries. Interestingly, a recent addition to the literature [26]
examined the increase in melatonin content from dietary
intake of Jert Valley cherries (seven varieties, none of
which were Montmorency tart cherries). They showed that
in a very small population of middle-aged and elderly
volunteers, there was an increase in urinary melatonin and
some modest improvements in sleep parameters. This
investigation [26] based its observations on the first
morning void only, whereas all urinary voids were captured
for a 48-h period during each part of the current trial. This
approach, whilst still having limitations, allows for cosinor
analysis and tracking of the circadian rhythm and provides
a more comprehensive picture of the dietary effects of
cherries on melatonin metabolism across the course of the
day. This is especially important when one considers that
the half-life of melatonin is relatively short and it is pos-
sible to miss fluctuations in melatonin throughout the day.
Further, there is no indication in the aforementioned
studies [8, 25] of an experimental control or record of
dietary intake, which makes interpretation of the data
problematic. Although we were not able to quantify the
exact nutritional content for each subject, food intake was
estimated. Participants replicated diet as closely as possible
from trial to trial. This was based on number of portions
thought to contain antioxidants—there were no differences
between trials. Support for the efficacy of this approach can
be seen by the fact that aMT6s and sleep parameters were
unchanged in baseline and placebo trials, whereas aMT6s
was significantly elevated in the cherry juice trial. Given the
dietary control used in the current investigation, coupled
with the significant changes melatonin, we can add support
to research showing cherries [26], and specifically in this
case, Montmorency cherries improve sleep parameters in
healthy individuals, which is likely due to the increase in
dietary melatonin. These data support previous work
showing improved sleep in healthy younger adults with
exogenous melatonin supplementation [14]; but addition-
ally, it provides a potential alternative to traditional mela-
tonin supplementation in the form of a functional food.
Table 2 Subjective sleep questionnaire variables for all conditions; values are mean (±SD)
Baseline placebo Placebo Baseline cherry juice Cherry juice
SE (%) 89.3 (7.3) 91.7 (4.0) 90.0 (6.2) 91.1 (4.9)
SOL (mins) 40.3 (31.6) 39.5 (23.2) 39.8 (25.6) 34.2 (20.5)
WASO (mins) 36.0 (33.0) 19.2 (31.2) 28.8 (30.6) 27.6 (28.2)
Naps (mins) 9.0 (15.1) 7.8 (10.7) 8.6 (13.2) 1.9 (3.5)*
TST (mins) 447 (60) 476 (31) 452 (49) 475 (30)
SET (%) 88.1 (6.8) 90.4 (4.4) 89.4 (5.8) 90.7 (4.9)
SE sleep efficiency, SOL sleep onset latency, WASO wake after sleep onset, total SET sleep efficiency total, TST total sleep time
* Denotes significantly different from all other conditions (P B 0.05)
Table 3 Actigraphy variables for all conditions; values are mean (± SD)
Baseline placebo Placebo Baseline cherry juice Cherry juice
SE (%) 82.8 (15.7) 84.1 (5.8) 83.9 (7.8) 86.8 (3.6)
SOL (mins) 28.9 (21.3) 30.5 (34.8) 29.1 (26.8) 21.4 (11.1)
Time in bed (mins) 491.8 (36.7) 492.2 (40.6) 490.0 (32.9) 514.7 (17.0)*
FRAGI (AU) 36.8 (8.2) 35.2 (9.3) 35.8 (8.9) 34.2 (7.6)
TST (mins) 392 (28) 380 (49) 385 (30) 419 (22)*
SET (%) 77.5 (5.9) 77.4 (8.5) 76.8 (6.9) 82.3 (3.6)*
Of the possible 80 data sets, 17 were excluded due to technical issues
SE sleep efficiency, SOL sleep onset latency, FRAGI fragmentation index, total SET sleep efficiency total, TST total sleep time
* Denotes significantly different from all other conditions (P B 0.05)
Eur J Nutr
123
The secretion of melatonin is influenced by light/dark
cycles and ultimately is instrumental in the sleep/wake
cycle [13]. From a physiological perspective, given that
endogenous melatonin influences core temperature and
facilitates sleep [14], it makes the expectation tenable that
increased exogenous melatonin will further facilitate
changes in core temperature and hence be responsible for
the improvements in sleep quality. Further work examining
the potential physiological outcomes (such as core tem-
perature and EEG in polysomnographic paradigms) from
exogenous melatonin, specifically from functional foods,
would be useful additions to the literature. In an attempt to
elucidate the relationship between the change in SET and
the change in melatonin, we conducted a Pearson’s corre-
lation coefficient analysis and found that there was a
modest relationship (r = 0.416, P [ 0.05), indicating that
other factors may influence the variables associated with
sleep quality. Importantly, a limitation with our data is that
*21% of the actigraphy data were missing, which may
have influenced this correlation and also the non-significant
trends in other actigraphy-dependent variables. Further-
more, 50% of our sample was women, and it is conceivable
that they were in different stages of the menstrual cycle,
which may also influence core temperature and hence the
propensity for sleep disturbance [27]. Future research
might wish to consider this issue in future experiments.
Melatonin is not the only candidate mechanism, given
that sleep regulation is also influenced by pro-inflammatory
cytokines [17]. Tart cherries have been shown to contain
numerous phenolic compounds that have anti-inflammatory
and antioxidant properties that can increase antioxidant
capacity [5, 26]. Furthermore, cherry juice has been shown
to decrease oxidative stress and inflammation following
strenuous exercise [5] making it possible that these anti-
oxidant and/or anti-inflammatory properties modulated
indices of sleep in this study, although this remains to be
demonstrated in an experimental model.
It has been previously speculated that the positive
effects on sleep seen from tart cherries might be due to
improvements in circadian regulation [8]. We observed no
changes in mesor, amplitude or acrophase, although there
was a trend towards a higher mesor (essentially equating to
the mean value across the circadian cycle). This is perhaps
not surprising given that the total urinary melatonin did
increase with cherry juice supplementation. An obvious
difference with the previous work lies within the subject
populations; Pigeon et al. [8] used older adults suffering
from moderate/severe insomnia and did not measure cir-
cadian rhythm or melatonin, whereas the current investi-
gation used asymptomatic younger adults (B37 years) and
did measure circadian rhythm and melatonin. Conceivably,
cherries might help regulate circadian rhythm in those with
disturbed sleep [8]; however, our evidence shows (from
cosinor analysis) that despite increased total sleep time and
improved sleep quality, this is not the case in asymptom-
atic, healthy younger adults. Notwithstanding this, aMT6s
levels are increased with tart cherry juice consumption, but
an investigation that examines elderly individuals, perhaps
with disturbed sleep, that incorporates measures of circa-
dian rhythms and sleep quality would be a valuable addi-
tion to the literature.
In conclusion, this is the first study to show direct evi-
dence that dietary supplementation with a tart Montmorency
cherry juice concentrate increases circulating melatonin and
can provide modest improvements in sleep time and quality
in healthy adults with no reported disturbed sleep. Although
the interaction of other phytochemicals cannot be com-
pletely ruled out, these data provide a mechanism of action
for the previously conjectural reports of improved sleep
quality with cherry juice supplementation. Subsequently,
Montmorency tart cherry juice concentrate might therefore
present a suitable adjunct intervention for disturbed sleep
across a number of scenarios in healthy and symptomatic
individuals.
Acknowledgments Gratitude is extended to Kelly Mitcheson for
her help in data collection and to CherryActive (Sunbury, UK) for
donating the cherry juice concentrate.
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