Effects of Chocolate Intake on Perceived Stress : A Controlled Clinical Study

Abstract

Cocoa polyphenols have been shown to reduce stress in highly stressed, as well as normal healthy individuals, we wondered whether commercially available chocolate could reduce perceived stress in medical students or not, so we decided to conduct this study.
Sixty students were divided into 3 groups (10 males + 10 females/group): i) Dark chocolate (DC) ii) Milk chocolate (MC) iii) White chocolate (WC). Subjects answered a PSS-10 (Perceived Stress Scale) questionnaire at baseline and after consumption of chocolate (40 g/day) for 2 weeks. Data were analyzed by using Microsoft Excel and SPSS version 20. Descriptive analyses were conducted. Means were compared across the study groups by One-Way ANOVA and within the same group by paired 't' test.
Mean stress scores compared between the groups by ANOVA revealed statistically not significant differences before (F =0.505; P=0.606) and after chocolate consumption (F=0.188; P=0.829). Paired 't' test compared stress scores means before and after chocolate supplementation within the same group and exhibited statistically significant decrease in DC (t = 2.341; p value = 0.03) and MC (t = 3.302; p value = 0.004) groups. Mean stress scores decreased, on average, by approximately 2 and 3 points in DC and MC groups, respectively, at 95% Confidence Interval. The difference was more evident and statistically significant in female students as compared to the males.
Consumption of 40 g of Dark and Milk chocolate daily during a period of 2 weeks appear to be an effective way to reduce perceived stress in females.

Full text

International Journal of Health Sciences, Qassim University, Vol. 8, No. 4 (Oct-Dec 2014)
Effects of chocolate intake on Perceived Stress; a Controlled Clinical Study
Ahmed Al Sunni, Rabia Latif
Department of Physiology, College of Medicine, University of Dammam, Saudi Arabia
Abstract:
Background: Cocoa polyphenols have been shown to reduce stress in highly stressed, as well as normal healthy individuals,
we wondered whether commercially available chocolate could reduce perceived stress in medical students or not, so we
decided to conduct this study.
Methods: Sixty students were divided into 3 groups (10 males + 10 females/group): i) Dark chocolate (DC) ii) Milk chocolate
(MC) iii) White chocolate (WC). Subjects answered a PSS-10 (Perceived Stress Scale) questionnaire at baseline and after
consumption of chocolate (40 g/day) for 2 weeks. Data were analyzed by using Microsoft Excel and SPSS version
20.Descriptive analyses were conducted. Means were compared across the study groups by One-Way ANOVA and within the
same group by paired ‘t’ test.
Results: Mean stress scores compared between the groups by ANOVA revealed statistically not significant differences before
(F =0.505; P=0.606) and after chocolate consumption (F=0.188; P=0.829). Paired ‘t’ test compared stress scores means before
and after chocolate supplementation within the same group and exhibited statistically significant decrease in DC (t = 2.341; p
value = 0.03) and MC (t = 3.302; p value = 0.004) groups. Mean stress scores decreased, on average, by approximately 2 and 3
points in DC and MC groups, respectively, at 95% Confidence Interval. The difference was more evident and statistically
significant in female students as compared to the males.
Conclusion: Consumption of 40 g of Dark and Milk chocolate daily during a period of 2 weeks appear to be an effective way to
reduce perceived stress in females.
Key words: Perceived Stress, Medical Students, Chocolate, Controlled Clinical Study
Corresponding Author:
Dr. Rabia Latif
Assistant Professor
Physiology Department
College of Medicine
University of Dammam
Phone: 00966 0596212648
Email: dr.rabialatif@gmail.com
rlhussain@ud.edu.sa

Effects of chocolate intake…
Introduction
Stress is defined as “the non-specific
response of the body to any demand for
change.” The effects of stress on public health
are profound. Researchers have related stress
to a number of diseasesranging from
cardiovascular disease to diabetes and even
various cancers. (1-4)
The stress associated with medical
students while undergoing medical education
is an accepted model of stress and produces
consistent findings. Nearly all medical colleges
have an authoritarian and rigid atmosphere
that encourages competition instead of
cooperation among learners.(5) Fairly high
levels of stress among medical students have
been documented worldwide.(6-10) A study
conducted in three British medical universities
found the prevalence of stress to be 31.2%. (11)
In Malaysia and Thai medical colleges, stress
prevalence was 41.9% (12) and 61.4% (13)
respectively. In Saudi Arabia, local
epidemiological data about stress among
medical undergraduate students are scarce.
Results of two recent studies from Saudi
Arabia have suggested high rates of stress (63
% and 71 %) among medical students. (14, 15)
The study of medicine is extensive,
laborious and very stressful especially during
preclinical study period. Students are
subjected to endless working hours, and
examinations. Peers, teachers or parental
pressures add an extra burden. Students often
have to work beyond their threshold strength to
get an outstanding grade-point-average.
Hence, medical students experience
considerable stress that may result in negative
academic, emotional and health outcomes. (16)
Attention must be directed to reduce the stress
in undergraduate medical education if we are
to maintain the commitment and enthusiasm in
the students.
Recent evidence showed that nutritional
interventions exert a beneficial effect on many
of the biological risk factors produced by
stress, (17) cocoa products being one of them.
Chocolate has been shown to reduce stress in
highly stressed, (18) as well as normal healthy
individuals (19) in two randomized controlled
studies. Since cocoa polyphenols could reduce
stress in highly stressed, as well as normal
healthy individuals, we wondered whether
commercially available chocolate could reduce
perceived stress in medical students or not.
Material and Methods
It was a non-randomized, parallel controlled
clinical study (CCS). Permission and ethical
approval to conduct the study was sought and
granted by the University Deanship of
Scientific Research. Since stress perception by
medical students is linked with their academic
year, (14) we targeted students from the same
academic year, positioned in the main
university campus, to be able to be contacted
easily as a group. Participants were drawn by
non-probability convenience sampling from 2nd
year Medicine class in our University.
Participation into the study was solely on a
voluntary basis and students who volunteered
were reassured that all information obtained
will be kept confidential and secure. Our
inclusion criteria were (i) non-smoker (ii) no
known chronic diseases such as diabetes,
coronary heart disease, or other major
illnesses (iii) willing to consume 40 g of the
chocolate daily for 2 weeks. Our exclusion
criteria included (i) use of any medication (ii)
known history of any illness (endocrinal,
metabolic, psychiatric) at recruitment (iii)
Pregnancy (iv) females who were expected to
undergo menstrual phase of uterine cycle
during chocolate eating phase, and (iv)
inaccessibility to follow up.
Sixty students (30 males, 30 females) from
2nd year medical class were recruited to
participate in the study. The subjects were
advised that the intake of cocoa and chocolate
other than the study chocolate be discontinued
1 week prior to the study and that this
restriction should be maintained throughout the
study period. Based on the type of chocolate
given, subjects were divided equally into 3
groups (10 males + 10 females/group) as
follows: i) Dark chocolate group (DC) ii) Milk
chocolate group (MC) and iii) White chocolate
group (WC).
The protocol of the study visit was as
follows: During the first visit before the
commencement of the study, subjects were
given information about the study, and, if the
consent was given, more specific instructions
were provided. At the first study visit, subjects
were divided into DC, MC and WC groups,
based on their own preference, and study
chocolates were given. The subjects were
instructed to consume the daily amount of
chocolate in a single portion. The composition,
nutrient content and calories per bar were
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Ahmed Al Sunni et al…
identical in DC, MC and WC except the
amount of cocoa solids (Table 1 and Figure 1).
Subjects were studied at baseline and after
consumption of chocolate (40 g/day) for
2 weeks. Data collection was accomplished by
using a questionnaire PSS-10 (Perceived
stress scale) which is the most widely used
psychological instrument for measuring the
perception of stress. It consisted of 10 items
that measured perceived stressful experiences
over the previous month with a 5-point Likert
scale ranging from never (=0), almost never
(=1), sometimes (=2), fairly often (=3) and very
often (= 4). (20) The PSS-10 has a possible
range of scores from 0 to 40. We used Arabic
version whose internal consistency reliability
assessed using Cronbach's α, was reported to
be 0.74. (21) Students answered the
questionnaire in direct supervision of either of
the two authors. Test-retest technique was
adopted to check the reliability and validity of
the questionnaire. Ten students asked to solve
the same questionnaire with a two weeks lag
to see if they answered in the same manner.
Table 1. Ingredients present in study chocolates
S.
No
Ingredients
Dark Chocolate
Milk Chocolate
White Chocolate
1 Cocoa solids Present Present Absent
2 Cocoa butter Present Absent Present
3 Cocoa processed with alkali
Absent Absent Present
4 Milk solids Absent Present Present
5 Milk fat Present Absent Absent
6 Lactose Absent Absent Present
7 Sugar Present Present Present
8 Emulsifier (Soya Lecithin) Present Present Present
9 Flavouring agent (Vanilla) Present Present Present
Figure 1. Amount of cocoa solids per bar
0
10
20
30
40
Dark
chocolate Milk
chocolate White
chocolate
% of Cocoa Solids
% of Cocoa Solids
395

Effects of chocolate intake…
Statistical Analysis
The collected data was entered in Microsoft
Excel spreadsheet; coding of the variables was
done. PSS scores were obtained by reversing
responses (e.g., 0 = 4, 1 = 3, 2 = 2, 3 = 1 and 4
= 0) to the four positively stated items (items 4,
5, 7 and 8) (22) and then summing across all
scale items. The scale yielded a single score,
with high scores indicating higher levels of
stress and low scores indicating lower levels of
stress. Statistical analysis of the coded data
was done by using SPSS version 20 and the
results were expressed as (Means ± standard
deviation). Difference between baseline and
end-point values within the pooled groups were
tested by paired ‘t’ test. Means were compared
across the study groups by One-Way ANOVA.
Differences with p values of 0.05 or less were
considered significant.
Results
Pre- and Post-chocolate consumption
perceived stress as reported by the students
has been shown in Table 2. Baseline stress
scores between the groups compared by
ANOVA revealed statistically insignificant
differences (F =0.505; P=0.606) (Table 3),
meaning that our groups were not different
from one another. Overall, compliance with the
nutritional instructions and restriction was
good, as none of the subjects reported
consumption of the restricted foods (cocoa and
chocolate products other than the study
chocolate). Mean stress scores among the
groups also did not differ significantly from one
another at the end of treatment; as revealed by
ANOVA (F=0.188; P=0.829) (Table 3). Paired
‘t’ test was used to compare the means of
stress scores before and after chocolate
supplementation within the same group and it
exhibited statistically significant differences in
DC (t = 2.341; p value = 0.03) and MC (t =
3.302; p value = 0.004) groups (Table 3). In
DC and MC groups, mean stress scores
decreased, on average, by approximately 2
and 3 points respectively at the 95%
Confidence Interval (95% CI). Thorough
probing of the results showed that the
difference was more evident and statistically
significant in female students as compared to
the males in DC and MC groups (Figure 2 and
3). In WC group, there were statistically
insignificant differences among pre- and post-
chocolate consumption mean stress scores in
males and females (Figure 4).
Table 2. Perceived stress as reported by the students Pre and Post-chocolate consumption
Questions
0
1 2 3 4
Never
Almost
never
Sometimes
Often
Very
often
No. (%) No. (%) No. (%) No. (%) No. (%)
1 In the last month, how often
have you been upset because
of something that happened
unexpectedly?
Pre 5 (8.3)
22 (36.7) 23 (38.3) 8 (13.3) 2 (3.3)
Post
8 (13.3)
21 (35) 22 (36.7) 7 (11.7) 2 (3.3)
2 In the last month, how often
have you felt that you were
unable to control the important
things in your life?
Pre 8 (13.3)
18 (30) 26 (43.3) 5 (8.3) 3 (5)
Post
8 (13.3)
28 (46.7) 16 (26.7) 7 (11.7) 1 (1.7)
3 In the last month, how often
have you felt nervous and
"stressed"?
Pre 1 (1.7) 11 (18.3) 19 (31.7) 22 (36.7)
7 (11.7)
Post
3 (5) 14 (23.3) 27 (45) 13 (21.7)
3 (5)
4 In the last month, how often
have you felt confident about
your ability to handle your
personal problems?
Pre 0
5 (8.3) 25 (41.7) 27 (45) 3 (5)
Post
0 0 12 (20) 37 (61.7)
11 (18.3)
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Ahmed Al Sunni et al…
5 In the last month, how often
have you felt that things were
going your way?
Pre 1 (1.7) 7 (11.7) 24 (40) 22 (36.7)
6 (10)
Post
1 (1.7) 6 (10) 22 (36.7) 29 (48.3)
2 (3.3)
6 In the last month, how often
have you found that you could
not cope with all the things that
you had to do?
Pre
6 (10) 20 (33.3) 27 (45) 5 (8.3) 2 (3.3)
Post
5 (8.3) 28 (46.7) 21 (35) 6 (10) 0
7 In the last month, how often
have you been able to control
irritations in your life?
Pre 1 (1.7) 5 (8.3) 23 (38.3) 28 (46.7)
3 (5)
Post
0 5 (8.3) 20 (33.3) 31 (51.7)
4 (6.7)
8 In the last month, how often
have you felt that you were on
top of things?
Pre 0 7 (11.7) 26 (43.3) 26 (43.3)
1 (1.7)
Post
0 6 (10) 18 (30) 33 (55) 3 (5)
9 In the last month, how often
have you been angered
because of things that were
outside of your control?
Pre
4 (6.7) 16 (26.7) 23 (38.3) 13 (21.7)
4 (6.7)
Post
6 (10) 14 (23.3) 26 (43.3) 12 (20) 2 (3.3)
10
In the last month, how often
have you felt difficulties were
piling up so high that you could
not overcome them?
Pre
7 (11.7)
12 (20) 23 (38.3) 17 (28.3)
1 (1.7)
Post
8 (13.3)
28 (46.7) 17 (28.3) 3 (5) 4 (6.7)
Table 3. Mean stress scores in all three groups.
Groups*
Perceived
Stress Scores (Mean ± SD)
T value
p-value
(Paired t test)
Baseline
Post-intervention
Dark Chocolate 17.65 ± 5.93 15.5 ± 6.09 2.341 0.03
Milk Chocolate 17.95 ± 4.50 14.55 ± 3.62 3.302 0.004
White Chocolate 16.35 ± 5.52 14.70 ± 5.75 0.930 0.364
p
-
value (ANOVA)
0.61 0.83
*(Number of subjects/group = 20)
397

Effects of chocolate intake…
Figure 2. Dark Chocolate Group Mean stress scores (Mean ± SD) pre and post intervention.
Figure 3. Milk Chocolate Group Mean stress scores (Mean ± SD) pre- and post-intervention.
17 ± 3.06
18.3 ± 8.00
14.6 ± 3.95
16.4 ± 7.81
0 5 10 15 20
Males
Females
Post-intervention stress scores
Baseline stress scores
16.1 ± 3.67
19.8 ± 4.66
14.7 ± 3.97
14.4 ± 3.44
0 5 10 15 20 25
Males
Females
Post-intervention stress scores
Baseline stress scores
398

Ahmed Al Sunni et al…
Figure 4. White Chocolate Group Mean stress scores (Mean ± SD) pre- and post-intervention.
Discussion
Dark chocolate and other cocoa products
have received lot of attention all over the
world as dietary supplements to improve
cardiovascular health. However the scientific
evidence those cocoa products may alleviate
stress as well is a relatively novel finding.
Stress and our body reaction to it is one of the
risks of coronary artery disease. In this regard,
if chocolate can buffer our response to stress,
this would be a novel cardio protective effect of
chocolate.
To the best of our knowledge, this is the
first study focusing on the effects of chocolate
supplementation on perceived stress in
medical students. The results of our study
demonstrate significant reduction in perceived
stress score after consuming dark and milk
chocolate for 2 weeks, more so in females than
in male students. Our results are in conformity
with a clinical trial (19) which provided strong
evidence that a daily consumption of 40 grams
of dark chocolate for two weeks reduced levels
of stress hormones in highly stressed people.
Our study results are also in agreement with a
recent randomized, placebo-controlled trial that
reported that those men who consume dark
chocolate had significantly lower levels of
cortisol and epinephrine (peripheral stress
hormones) compared to control subjects after
a mock psychosocial stress test. (18) However
the ACTH levels (central stress hormone) were
identical in both groups. The researches
concluded that dark chocolate intake blunted
the body’s response to the brain signals of
stress. In particular, the response of the
adrenal gland, which produces cortisol, was
much less. Wirtz et al., (18) also assessed
cognitive stress appraisal by using the Primary
Appraisal Secondary Appraisal (PASA)
questionnaire. It was noticed that, since the
body stress response was less significant, men
consuming dark chocolate reported having less
feelings of stress during the process as
compared to the control subjects. The
decrease in the mean stress scores after
consumption of white chocolate was
statistically not significant.
This shows that the blunting of the
perceived stress was not due to sweet nature
of dark or milk chocolates but due to cocoa
solids which were present in dark and milk
chocolate butwere absent in white chocolate.
Cocoa solids are one of the richest sources
of flavanol antioxidants. (23) The link between
16.9 ± 5.00
15.8 ± 6.21
15 ± 6.27
14.4 ± 5.50
13 14 15 16 17 18
Males
Females
Post-intervention stress scores
Baseline stress scores
399

Effects of chocolate intake…
stress and oxidative status in human body is
now well-established. It has been
demonstrated that stress increases lipid
peroxidation and an imbalance between
antioxidant enzyme activities. (24) In this
perspective, antioxidants supplementation is
considered as a beneficial strategy for
improving stress. (25,26) There is a strong
possibility that flavonoid rich chocolate
supplementation might have acted through a
modulation of oxidative status, that is the
enhancement of endogenous antioxidant
defense and the subsequent reduction of
oxidative stress. Nevertheless, further
studiesare needed to confirm this hypothesis,
and the exact mechanism of action remains to
be explored.
The observed gender-specific difference in
perceived stress scores following chocolate
intake may be partly attributed to effects of sex
hormones. (27, 28) Scientific evidence shows that
hypothalamic-pituitary-adrenal axis response
during the stress differs markedly between
males and females and there is an increased
sensitivity of the adrenal cortex in women as
compared to men. (29) Future studies are
warranted in post-menopausal women to see
whether these gender differences persist or
diminish after menopause. Last but not the
least, the benefits of chocolate need to be
carefully considered with the calories
consumed.
Conclusions
Dark and Milk chocolate appear to be an
effective way to reduce perceived stress in
females.
Limitation
Our study was based on self-reported
information provided by students. Therefore,
there is some probability for reporting bias. To
ensure treatment compliance, the study was
non- randomized. The students chose whether
they preferred Dark, Milk or White
Chocolate.This non-randomization means
failure of the blinding of the identity of
treatments from participants, investigators and
assessors. Therefore, one should be cautious
in drawing cause and effect hypothesis from
our results. Last but not the least; small sample
size in each group was also one of the
limitations.
Acknowledgement
The authors acknowledge the financial
support provided by the Deanship of Scientific
Research, University of Dammam for this
study.
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