the effect of energy drinks on the cognitive function in medical students

The effect of energy drinks on the cognitive function in medical students: Randomised controlled trial. American Journal of Food Science and Health. 5(3), 126-141 3000 words, give or take 10% There are no heading requirements for Section B. Reference list and in-text citations are NOT required for either Section A or B in this assessment.

American Journal of Food Science and Health
Vol. 5, No. 3, 2019, pp. 126-141
http://www.aiscience.org/journal/ajfsh
ISSN: 2381-7216 (Print); ISSN: 2381-7224 (Online)
* Corresponding author
The Effect of Energy Drinks on the Cognitive
Function in Medical Students: Randomised
Controlled Trial
Raehan Hemanth*
, Tan Min En, Lee Wen Hui,
Dolamulla Kankanamge Dilhan De Silva
Faculty of Medicine, Melaka Manipal Medical College (Manipal Academy of Higher Education), Melaka, Malaysia
Abstract
Energy drinks can be defined as any non-alcoholic beverage that primarily contains caffeine, taurine, glucose derivatives,
vitamin B and some herbal ingredients. Energy drinks have become a popular drink especially among the adolescent to young
adult population. This randomised controlled study was conducted to determine the effect of energy drinks on the cognitive
function among medical students. A randomised controlled trial was carried out in a private medical college in Malaysia from
June 2019 to July 2019. The participants were randomized into two groups: an intervention group (energy drinks) and a control
group (non-caffeinated carbonated beverages) with 26 participants in each group respectively. They were asked to perform
short term memory, attention, and reaction time tests, along with assessing their alertness and anxiety levels. They were given
250ml of either an energy drink (Monster) or control drink (Sprite). After 30-45 minutes, they were once again evaluated for
their cognitive performance, alertness, anxiety levels and immediate adverse effects were asked. The changes in the cognitive
performance, alertness and anxiety level were analysed using unpaired t test and paired t test. The immediate adverse effects
after consuming the beverages were analysed using Chi-square test and Fisher exact test. The results showed that there were
significant differences in the levels of alertness but no significant differences were observed in short term memory, reaction
time and selective attention while comparing intervention and control groups after consumption of the drinks. There was a
significant difference however, in reaction time (p=0.020), selective attention (p=0.023), and levels of alertness (p<0.001) and
anxiety (p=0.010) after consuming the energy drinks in comparison to the performance prior to the intervention. There was no
significant difference in the immediate adverse effects and the consumption of both beverages. In conclusion, energy drinks
can improve reaction time, selective attention and the levels of alertness but the participants experience an average increase in
anxiety level after consumption of these popular drinks. On the contrary however, energy drinks have no effect on short term
memory.
Keywords
Energy Drinks, Cognitive Function, Medical Students, Randomised Controlled Trial
Received: July 15, 2019 / Accepted: October 7, 2019 / Published online: October 29, 2019
@ 2019 The Authors. Published by American Institute of Science. This Open Access article is under the CC BY license.
http://creativecommons.org/licenses/by/4.0/
1. Introduction
“Energy drinks” can be considered as any non-alcoholic
beverage that usually contains caffeine (a psychostimulant),
as well as sugar and often additional supplements, that are
perceived to improve alertness and physical performance
[1]. The sales of energy drinks have grown into a global
billion-dollar industry. For instance, since Red bull®
127 Raehan Hemanth et al.: The Effect of Energy Drinks on the Cognitive Function in Medical Students:
Randomised Controlled Trial
launched their products into the markets of Austria in 1987
and into the United States in 1997, the company’s growth
was astounding due to their marketing strategy in
promotion of its sales among the younger generation [2].
The content of these energy drinks are mainly caffeine,
taurine, glucose derivatives, riboflavin, pyridoxine,
nicotinamide, and other vitamin B and other herbal
ingredients such as ginseng guarana and gingko biloba [1].
According to Zenith International [3], the consumption of
energy drinks worldwide has increased since 2007 by 14%,
reaching 4.8 billion litres in 2011, from a previous value of
3.3 billion litres. In a study done in the European Union in
2012, the prevalence of consumption of energy drinks is
68% among young adults, 30% in adults and 18% in the
paediatric age group [1]. Bulut et al. [4] noted that 46.5% of
university students in Turkey have a history of consuming
energy drinks at least once. Park et al. found that 1.4% of
students among the 800 students sampled consumed energy
drinks more than 5 times a week, whereas 10.5% drank it at
least once a week in South Korea [5]. This is supported by
the 665% growth spurt in the energy drink industry in South
Korea between the years of 2010 to 2012 [6]. In a study
done in Malaysia among university students, 83.3%
consume energy drinks, 31.7% take it weekly and 5.8%
daily, in which the common energy drink brands are Red
bull®
, Livita®
and Power root®
[7].
Many studies have been done to determine the active
ingredient in energy drinks that enhance cognitive function.
Giles et al. [8] states that caffeine is the active ingredient in
energy drinks that bring about improvements in mental
performance, drives away lethargy and increases attention
and reaction time. However, some studies state that it might
be due to the withdrawal effect of caffeine that results in
these improvements [9]. On the other hand, Hewlett et al.
[10] found that mood and cognitive function were not
affected by overnight caffeine withdrawal and caffeine
helps people stay awake and remain vigilant. This is further
supported by Warburton et al. [11] as information
processing, attention and verbal reasoning has been greatly
enhanced by moderate intake of caffeine and taurine.
Scholey et al. found that there might be a synergistic effect
between glucose and caffeine resulting in the enhancement
of cognitive performance [12].
In addition, consuming energy drinks resulted in significant
improvement in alertness, thus enhancing physical
endurance and cognitive function [13]. This is supported by
Lara et al. [14] as the physical performance of athletes
improved greatly in a simulated soccer game. Furthermore,
energy drinks can be used as a stimulant to increase
alertness in a sleep deprived person to prevent the driver
from dozing off [15].
Mixing energy drinks and alcohol however, further affects
behavioural inhibition and mask signs of intoxication, thus
endangering their lives especially while driving as it may
lead to road traffic accidents [16]. Excessive energy drink
intake might precipitate seizure attacks [17]. Energy drink
consumption has a negative relationship with the number of
hours of sleep someone attains after consuming the
beverage, resulting in insomnia, and is also associated with
depressive mood [5]. Furthermore, obese individuals should
be cautious during the intake of energy drinks as it might
lead to adverse cardiovascular effects [18]. Pettit et al. [19]
also established a negative relationship between academic
performance and the intake of energy drinks. This might be
due to latent sleep onset, insomnia and increased daytime
sleepiness [20].
In previous intervention studies, Alford et al. [13] found
that there was marked improvement in cognitive functions
such as reaction time, memory and concentration, which
was evident by the elevated alertness demonstrated by the
subjects. In addition, according to the results attained by
Kennedy et al. [21], combining caffeine and glucose can
enhance cognitive function and circumstantial fatigue
during lengthy periods where increase cognitive demand is
required. This is also supported by Adan et al. that caffeine
and glucose help in improving attention and consolidation
of verbal memory [22]. However, in another study, short
term memory is not improved by the combination of
caffeine and taurine which are the assumed active
ingredients of energy drinks [23]. Warburton et al. [11] also
found that taurine containing energy drinks had no effect on
verbal memory compared to placebos.
According to Euromonitor International 2014 [24], the
growth rate of sales of energy drinks in Malaysia from the
year 2008-2013 is 24.5%. This indicates that the industry of
energy drinks in Malaysia has increased exponentially and
energy drinks are becoming more popular among the
citizens. Previous research has been done in Malaysia on
the effect of energy drinks on cardiology parameters and
they found out that energy drinks can raise systolic blood
pressure and there was a significant improvement in mental
alertness subjectively [25]. On the other hand, another study
done among a local university found that there was no
significant difference between the academic performance of
students who consume energy drinks and those who do not
[7]. Therefore, this randomised controlled study is being
conducted to determine the effect of energy drinks on the
cognitive performance among medical students.
The main objective of this study is to determine the effect
of energy drinks (Monster®
) compared to a control drink on
cognitive function (short term memory, attention and
reaction time). Furthermore, we would like to find out the
American Journal of Food Science and Health Vol. 5, No. 3, 2019, pp. 126-141 128
immediate adverse effects of energy drinks. Our research
questions are:
A. Do energy drinks (Monster®
) affect the cognitive
function (short term memory, attention and reaction time)
of medical students?
B. Do energy drinks have any immediate adverse effects?
From this research, we would hypothesize that the
consumption of energy drinks will improve short term
memory, attention and reaction time in medical students.
2. Methodology
2.1. Study Design, Study Setting and Study
Population
We conducted a randomised controlled trial to determine
the effect of energy drinks on cognitive function in which
short term memory, reaction time and attention were
assessed. This study was conducted among medical
students of Melaka Manipal Medical College (MMMC),
Muar campus, Malaysia.
MMMC has two campuses (Melaka and Muar) in
Malaysia which cater for students from Foundation in
Science (FIS), Bachelor of Dental Surgery (BDS) and
Bachelor of Medicine and Bachelor of Surgery (MBBS).
Our study was conducted in the month of June 2019 till
July 2019, in MMMC in Muar, Johor, Malaysia where
semester 6 and 7 MBBS students with a population
estimated to be around 280 students were situated.
2.2. Sample Size and Sampling
Out of the estimated 280 population in Muar campus, we
conducted a non-probability sampling where we invited
volunteers to obtain a sufficient sample for our study. The
sample size was calculated using the below formula where
0.05 precision (α=0.05) was accepted.
To compare the quantitative outcome between energy
drinks (Monster) and a control drink, a formula comparing
two means (using mean and standard deviation) in
Statistics and Sample Size Pro app was used as shown
below:

+

+

The minimum sample size was calculated with the help of
previous study
Where,
Type 1 error rate (α)=0.05
Type 2 error rate (β)=0.2
Mean in group 1 (µ1)=89.62
Standard deviation in group 1 (σ1)=2.49
Mean in group 2 (µ2)=86.43
Standard deviation in group 2 (σ2)=5.15
Ratio (Group 2/Group 1)=1
With reference to a previous similar study, the mean
percentage of getting the right answer of spatial memory is
89.32% and 86.43% for energy drinks and placebo’s
respectively [12]. The minimum sample size needed for each
group was 26 (per intervention group).
n =
!%# (1)
n = $
%.
(2)
n = 28.89 (3)
n ≈ 29 (4)
Dropout percentage=0.1
n=26
With 10% as attrition, the final sample size, nfinal calculated
from the formula above was 29 per group. Therefore, the
total minimum sample size needed was 58. However, we
recruited 52 students as our final total sample size. We
randomized 52 students into 2 groups, which included 26
students in the intervention group and 26 students in the
control group.
The sampling method used was the non-probability sampling
method. Our inclusion criteria were medical students from
semester 6 and 7 of any age, gender, ethnicity and who were
willing to provide informed consent. The exclusion criteria
consisted of significant medical illnesses or mental disorders,
use of specific medication, signs and symptoms of
dysmenorrhea (for females), alcohol consumption in the last
24 hours and caffeinated drink consumption within the last
10 hours. Volunteers were selected based on fixed inclusion
and exclusion criteria.
2.3. Randomization
We recruited 52 volunteers to participate in this study, in
which 26 volunteers were allocated to the intervention group
and 26 volunteers were allocated to the control group. The
block randomization method was done to randomize equal
numbers of participants into the respective intervention group
and control group. Therefore, a block size of 2 was used to
classify the participants into an intervention group and
control group. We used Randomizer. org website to carry out
the randomization.
129 Raehan Hemanth et al.: The Effect of Energy Drinks on the Cognitive Function in Medical Students:
Randomised Controlled Trial
2.4. Procedure and Intervention
Figure 1. Flow chart of the randomised controlled trial.
Participants were then be divided into a control group and an
intervention group. All of the participants were given a
questionnaire prior to the commencement of the tests to
assess their validity in terms of exclusion criteria, which was
applied to exclude participants who consumed alcohol in the
last twenty-four hours, consumed caffeinated drinks in the
last ten hours, had significant medical illnesses and mental
disorders, used specific medication, and exhibited signs and
symptoms of dysmenorrhea for females. Then, a selfadministered questionnaire was distributed to assess the
participant’s sleeping pattern, nutritional status, caffeine
intake, energy drink intake, exercise tolerance and practices
of self-meditation. The participants were also asked to rate
how energetic, awake, anxious and alert they were feeling
from a scale of 1-10 prior to the commencement of any tests.
After the questionnaires were analysed for their validity for
partaking in the tests, a pre-test was conducted prior to the
consumption of the control and intervention drinks to assess
the simple reaction time, selective attention and short-term
memory of the individual participants. The individual scores
were then documented and used for later comparison with the
results attained after the intervention.
For the intervention group, they were assigned to drink an
energy drink (Monster®
, in which every 100ml contained
47kcal calories, 0g protein, 0g fat, 12.2g carbohydrate, 11.3g
total sugar, 77mg sodium, 19mg caffeine, 400mg taurine) 30
to 45 minutes prior to the initiation of the test and the control
group was provided a non-caffeinated carbonated beverage
(Sprite®
, in which every 100ml contained 22kcal calories, 0g
protein, 0g fat, 5.5g carbohydrate, 5.5g total sugar, 16mg
sodium) to drink at the same time as the intervention group.
The amount to be consumed was kept constant for all
participants regardless of the drink, at an estimated 250ml.
Therefore, each participant assigned to the intervention group
consumed an energy drink containing 47.5mg caffeine and
28.25g total sugar, whereas the control group consumed a
American Journal of Food Science and Health Vol. 5, No. 3, 2019, pp. 126-141 130
non-caffeinated carbonated drink which contained 13.75g
total sugar. 30-45 minutes after consuming the drinks, all the
participants were once again asked to take the same tests to
assess their simple reaction time, selective attention and
short-term memory. The individual scores were once again
documented for analysis. Once the tests were completed, all
the participants were provided another questionnaire to once
again assess and enquire about the presence of any adverse
effects after the intervention was completed. The specific
adverse effect of insomnia was asked about the following
morning. The participants were also asked to rate how
energetic, awake, anxious and alert they were feeling from a
scale of 1-10 after the completion of the tests. To ensure a
non-biased result, our intervention was held in the computer
lab at the same time for all participants with no outside
interference.
2.5. Cognitive Function Test
1) Simple reaction time [26]
This test can assess response speed and accuracy. The
participant was instructed to click on the screen once the
screen changes colour from red to green. The reaction time
was recorded in milliseconds. The average score of 5 trials
was documented.
2) Forward Digit span (numerical memory) [26]
This test measured short term memory span. The participant
was asked to memorise the sequence of numbers which
appeared on the screen and type out the number after the
numbers disappear. The number of digits increased with each
correct answer and the performance was documented by the
average number of digits correctly remembered.
3) Verbal short-term memory [26]
This test assessed short term memory in which the
participants had to remember the previous words shown on
the screen and decide whether or not the word projected had
already been shown or was a new word. The marks are
calculated based on the number of correct answers and the
participants were given 3 chances.
4) Visual memory test [26]
This test measured spatial short-term memory where it
assessed the participant’s ability to remember relationships
between objects in space. The participant had to pay attention
and memorise the sequence of the boxes while they start to
flash and click the correct order of previously flashing boxes.
The performance was measured by the average number of
boxes remembered during the task.
5) Stroop effect [27]
This test assessed the selective attention and their processing
speed ability. A video was played to assess the Stroop effect
in which there was a mismatch between the ink colour and
the word. The participant had to write down the colour of the
ink of the word. The performance was assessed based on the
number of correct answers.
2.6. Data Collection and Data Processing
On the day of data collection, the participants were called to
the computer lab and they were seated according to the group
they belonged to. At the beginning, the participants were
briefed about the aim and their role in the experiment. They
were informed that they were allowed to withdraw from the
study at any time they wanted.
The participants were given the questionnaire to assess their
mental alertness subjectively and the cognitive function was
assessed through online cognitive tests
(https://www.humanbenchmark.com/). The baseline variables
were BMI (Body Mass Index), number of hours of sleep the
day before, caffeinated drink intake, consumption of energy
drinks, self-meditation and nutritional status.
Then, they were given the respective intervention and control
drinks allocated to them and the participants reassembled at
the computer lab after a duration of 30-45 minutes in which
they were not allowed to do any form of strenuous activity.
Their cognitive function (simple reaction time, selective
attention and short-term memory, which included verbal,
numerical and visual memory) was assessed again postintervention.
2.7. Data Analysis
For the data analysis, it was tabulated by using Microsoft
Excel version 2013 and the values entered were double
checked to prevent any duplication and prevent missing data.
From Microsoft Excel, the information was then used for
statistical calculation using analytical software Epi info
version 7.2 and Graph pad.
For descriptive statistical analysis, we included mean,
standard deviation (SD), frequency and percentage. Mean
and standard deviation were used to analyse age, BMI,
alertness scale and average hours of sleep. Frequency and
percentage were calculated for categorical data which
included gender, ethnicity, caffeinated drink consumption,
energy drink intake, average hours of exercise per week and
adverse effects of energy drinks. A table was drawn for the
demographic details to describe frequency and its percentage
between the intervention group and control group.
For hypothesis testing, a parametric test known as unpaired t
test was used to determine the difference between the
intervention group and control group on cognitive
performance, alertness and anxiety levels. The level of
131 Raehan Hemanth et al.: The Effect of Energy Drinks on the Cognitive Function in Medical Students:
Randomised Controlled Trial
significance was set at P<0.05, in which any value more than
0.05 was considered not statistically significant. Paired t test,
another parametric test, was used to find the difference in
cognitive performance, alertness and anxiety levels before
and after consumption of the drinks. Mean plot was used to
represent the numerical data obtained from the scores of
cognitive performance, alertness and anxiety levels.
For measurement of association, the relative risk of adverse
effects after drinking the beverages between the intervention
and control groups was calculated along with 95%CI. Chisquare test and Fisher exact test were used to determine the
level of significance.
2.8. Ethical Consideration
The participants that joined the study were volunteers and
were not forced into partaking in the randomised controlled
trial. An informed consent form which mentioned all the
important necessary and relevant details of the study was
provided to each participant with a brief statement of
reassurance that there would be no academic or occupational
penalty on those who refused to volunteer for the study. Once
given the consent, each participant was given the free choice
to either partake or not, depending on how comfortable they
were with the tests to be conducted. The participants were
also notified well in advance, that all the data and
information gathered throughout the duration of the study
would be kept completely private and confidential. The
participants were also informed that they were allowed to
withdraw from the study at any time without reason. The
study was approved by the Research Ethics Committee,
Faculty of Medicine, Melaka Manipal Medical College
(MMMC).
3. Results
Table 1. Baseline characteristics between the intervention (energy drink) group (n=26) and control (non-caffeinated carbonated beverage) group (n=26).
Variables Energy drink Intervention
group (n=26) n (%)
Control group
(n=26) n (%)
Total (n=52) N
(%)
Age (years)a
22.7 (1.01) 22.9 (1.75) 22.8 (1.42)
Gender Male 11 (42.31) 15 (57.69) 26 (50)
Female 15 (57.69) 11 (42.31) 26 (50)
Ethnicity
Malay 1 (3.85) 2 (7.69) 3 (5.77)
Chinese 11 (42.31) 10 (38.46) 21 (40.38)
Indian 8 (30.77) 8 (30.77) 16 (30.77)
Others 6 (23.08) 6 (23.08) 12 (23.08)
BMI (kg/m2
)
a
23.69 (6.55) 22.88 (5.21) 23.29 (5.87)
Duration of sleep last night (hours)a
5.62 (1.57) 5.77 (1.93) 5.69 (1.74)
Meal before test Yes 23 (88.46) 21 (80.77) 44 (84.62)
No 3 (11.54) 5 (19.23) 8 (15.38)
Regular caffeinated drink consumer Yes 15 (57.69) 11 (42.31) 26 (50)
No 11 (42.31) 15 (57.69) 26 (50)
Frequency of consuming caffeinated drinks
Less than once a week 12 (46.15) 12 (46.15) 24 (46.15)
2-3 times a week 7 (26.92) 9 (34.62) 16 (30.77)
4-6 times a week 3 (11.54) 4 (15.38) 7 (13.46)
7-9times a week 2 (7.69) 1 (3.85) 3 (5.77)
More than 10 times a week 2 (7.69) 0 (0) 2 (3.85)
Energy drink consumer Yes 18 (69.23) 13 (50) 31 (59.62)
No 8 (30.77) 13 (50) 21 (40.38)
Duration of exercise per week
Less than 1 hour 10 (38.46) 11 (42.31) 21 (40.38)
1-2hour 8 (30.77) 6 (23.08) 14 (26.92)
3-4 hours 2 (7.69) 2 (7.69) 4 (7.69)
5-6 hours 4 (15.38) 3 (11.54) 7 (13.46)
7 hours and above 2 (7.69) 4 (15.38) 6 (11.54)
Self-meditation Yes 7 (26.92) 7 (26.92) 14 (26.92)
No 19 (73.08) 19 (73.08) 38 (73.08)
aMean (SD).
A total of 52 students participated in this study and were
randomised into two groups, which was the energy drink
intervention group (n=26) and control group (n=26). Table 1
shows baseline characteristics between the intervention group
(energy drinks) and control group (non-caffeinated
carbonated beverages). The mean age of participants in the
intervention group was 22.7 (SD=1.01), while in the control
group, the mean age was 22.9 (SD=1.75). For gender, female
participants were the majority (57.69%) in the intervention
group, however males were the majority (57.69%) in the
control group. The majority of participants were Chinese,
which was represented by 42.31% in the intervention group
and 38.46% in the control group. The average BMI in the
intervention group is 23.69 kg/m2
(SD=6.55) and 22.88
American Journal of Food Science and Health Vol. 5, No. 3, 2019, pp. 126-141 132
kg/m2
(SD=5.21) in the control group. Participants in the
control group had more hours of sleep which was 5.77 hours
(SD=1.93), compared to 5.62 hours (SD=1.57) in the
intervention group. Majority of the participants (84.62%) had
their meal before joining the study. 50% of the participants
were regular caffeinated drink consumers, in which 57.69%
are in the intervention group and 42.31% in the control group.
However, 46.15% of the participants consumed caffeinated
drinks less than once a week. The majority (59.62%) of the
participants have consumed energy drinks, which was
69.23% and 50% in the intervention group and control group
respectively. Majority of the participants (40.38%) exercised
less than 1 hour per week and 14% of the participants
performed self- meditation.
Table 2. Energy drink intake among energy drink consumers (n=31) between the intervention group (energy drink) and control group (non-caffeinated
carbonated beverage).
Variables Energy drink Intervention
group (n=18) n (%)
Control group (n=13)
n (%)
Total (n=31) n
(%)
Consumed more than 1 energy drink per month Yes 5 (27.78) 4 (30.77) 9 (29.03)
No 13 (72.22) 9 (69.23) 22 (70.97)
Brand of Energy Drink
Livita Yes 1 (5.56) 1 (7.69) 2 (3.85)
No 17 (94.44) 12 (92.31) 50 (96.15)
Power Root Yes 1 (5.56) 0 (0.00) 1 (1.92)
No 17 (94.44) 13 (100.00) 51 (98.08)
Monster Yes 1 (5.56) 1 (7.69) 2 (3.85)
No 17 (94.44) 12 (92.31) 50 (96.15)
Red Bull Yes 18 (100.00) 13 (100.00) 31 (59.62)
No 0 (0.00) 0 (0.00) 21 (40.38)
Amount of energy drinks consumed at once 1 17 (94.44) 13 (100.00) 30 (96.77)
2 1 (5.56) 0 (0.00) 1 (3.23)
Maximum amount of energy drinks consumed in a day a 1.94 (1.73) 2.38 (1.26) 2.13 (1.54)
Amount of energy drinks consumed per week
0 times 15 (83.33) 8 (61.54) 23 (74.19)
1-2 times 3 (16.67) 3 (23.08) 6 (19.35)
3-4 times 0 (0.00) 2 (15.38) 2 (6.45)
aMean (SD).
Table 2 shows the energy drink intake among energy drink
consumers between the intervention and control groups. The
sample size obtained for the study was 52 medical students.
However, only 31 of them reported that they had consumed
energy drinks prior to the study, therefore, the subset
obtained was 31 medical students. 18 of which belonged to
the intervention group (energy drinks) and 13 of them
belonged to the control group (non-caffeinated beverages).
Among the intervention group, 5 (27.78%) of them had
consumed more than one energy drink a month prior to the
study as compared to the 4 (30.77%) in the control group. 13
(72.22%) had never consumed more than one energy drink a
month among the intervention group whereas 9 (69.23%) had
never drank more than one energy drink per month in the
control group.
The four energy drinks enquired about here, were the four
main popular brands of energy drinks among Malaysian
medical students; Red Bull®
, Monster®
, Power Root®
and
Livita®
. Among the intervention group, only 1 (5.56%)
participant had reported drinking Monster®
or Livita®
before
as compared to the 17 (94.44%) participants who have never
consumed it. Among the control group, 1 (7.79%) participant
had consumed Livita®
and Monster®
before as opposed to the
12 (92.31%) who had never. In the intervention group, 1
(5.56) participant had taken Power Root®
before and 17
(94.44%) had never as compared to the control group where
all 13 (100.00%) participants reported never consuming
Power Root®
before. The most popular energy drink among
the four enquired about is Red Bull®
. In the intervention and
control groups, all 18 (100.00%) and 13 (100.00%) students
respectively had consumed Red Bull®
before.
The amount of energy drinks consumed at once was also
asked among the volunteers in the study. In the intervention
group, 17 (94.44%) of them reported that they had only taken
1 energy drink at a time whereas 1 (5.56%) participant had
reported to take 2 energy drinks at once. In the control group
however, all 13 (100.00%) students said to have consumed
only one energy drink at once.
The amount of energy drinks taken a week was subdivided
into 0 times, 1-2 times and 3-4 times a week. In the
intervention group, 15 (83.33%) did not take energy drinks
quantified to per week, 3 (16.67%) students had taken energy
drinks 1-2 times a week and no one reported to have taken it
3-4 times a week. As compared to the control group, 8
(61.54%) students did not take energy drinks quantified to
per week, 3 (23.08%) students took it 1-2 times a week and 2
(15.38%) took it 3-4 times a week.
Finally, the mean and standard deviation was calculated to
compare the maximum amount of energy drinks consumed in
a day between the intervention and control groups. For the
intervention group, the mean was 1.94 with a SD of 1.73 and
the control group had a mean of 2.38 with a SD of 1.26. The
133 Raehan Hemanth et al.: The Effect of Energy Drinks on the Cognitive Function in Medical Students:
Randomised Controlled Trial
overall mean and SD for the intervention and control groups was 2.13 and 1.54 respectively.
Table 3. Comparison of simple reaction time, short term memory, selective attention, alertness and anxiety between intervention group (energy drink) and
control group (non-caffeinated carbonated beverage) before intervention.
Outcome variables Mean (SD) Mean difference (95%CI) t-statistics (df) P-value Intervention group (n=26) Control group (n=26)
Cognitive
performance
Reaction time (ms) 296.96 (53.66) 331.00 (100.81) -34.04 (-79.02, 10.95) -1.52 (50) 0.135
Numerical memory (score) 10.31 (1.83) 9.00 (1.67) 1.31 (0.33, 2.28) 2.69 (50) 0.010
Verbal memory (Score) 33.69 (24.20) 35.65 (26.36) -1.96 (-16.05, 12.13) -0.28 (50) 0.781
Visual memory (score) 9.69 (2.68) 9.04 (1.66) 0.65 (-0.59, 1.90) 1.06 (50) 0.295
Selective attention (score) 26.62 (8.20) 28.46 (4.94) -1.85 (-5.62, 1.93) -0.98 (50) 0.330
Alertness
& anxiety
Alert (scale) 6.62 (1.88) 6.35 (1.74) 0.27 (-0.74, 1.28) 0.54 (50) 0.594
Awake (scale) 6.77 (2.01) 6.23 (1.88) 0.54 (-0.55, 1.62) 1 (50) 0.323
Energetic (scale) 6.15 (1.89) 5.58 (2.12) 0.58 (-0.54, 1.70) 1.04 (50) 0.305
Anxious (scale) 4.00 (2.61) 3.15 (2.11) 0.85 (-0.48, 2.17) 1.29 (50) 0.204
bUnpaired t-test.
Table 3 shows the comparison of simple reaction time, short
term memory, selective attention, alertness and anxiety
between the intervention and control groups before the
commencement of the intervention.
The mean of the participants’ reaction time in the intervention
group (energy drinks) was 296.96ms with standard deviation
(SD) of 53.66, while in the control group, the mean was 331ms
with SD of 100.81. The mean difference (95% CI) and tstatistics of reaction time between the intervention group and
control group were -34.04 (-79.02, 10.95) and -1.52 respectively.
The P value obtained for reaction time is 0.135. Hence, there is
no significant difference in the reaction time between the
intervention group and control group before the consumption of
the drinks.
The mean of the participants’ numerical memory score in the
intervention group (energy drink) was 10.31 with a SD of
1.83, while in the control group, the mean was 9.00 with a
SD of 1.67. The mean difference (95% CI) and t-statistics of
the numerical memory score between the intervention group
and control group was 1.31 (0.33, 2.28) and 2.69 respectively.
The P value computed for numerical memory was 0.010.
Hence, there is significant difference in the numerical
memory between the two groups before consumption of the
drinks.
The mean of the participants’ verbal memory score in the
intervention group (energy drinks) was 33.69 with a SD of
24.20, while in the control group, the mean was 35.65 with a
SD of 26.36. The mean difference (95% CI) and t-statistics of
verbal memory score between the intervention group and
control group was -1.96 (-16.05, 12.13) and -0.28
respectively. The P value computed for verbal memory was
0.781, which suggested that there is no significant difference
in the verbal memory between the intervention group and
control group before the intervention ended.
The mean of the participants’ visual memory score in the
intervention group (energy drink) was 9.69 with a SD of 2.68,
while in the control group, the mean was 9.04 with a SD of
1.66. The mean difference (95% CI) and t-statistics of the
visual memory score between the intervention group and
control group was 0.65 (-0.59, 1.90) and 1.06 respectively.
The P value obtained for visual memory was 0.295, which
suggested that there is no significant difference in the visual
memory between the intervention group and control group
before consumption of the drinks.
The mean of the participants’ selective attention score in the
intervention group (energy drinks) was 26.62 with SD of
8.20, while in the control group, the mean was 28.46 with SD
of 4.94. The mean difference (95% CI) and t-statistics of the
selective attention score between the intervention group and
control group was -1.85 (-5.62, 1.93) and -0.98 respectively.
The P value gained for selective attention score was 0.330.
Thus, there is no significant difference in the selective
attention score between the intervention group and control
group before the intervention.
The mean score of the participants’ level of alertness in the
intervention group (energy drink) was 6.62 (out of 10) with a
SD of 1.88, while in the control group, the mean was 6.35
with a SD of 1.74. The mean difference (95% CI) and tstatistics of alertness between the intervention group and
control group was 0.27 (-0.74, 1.28) and 0.54 respectively.
The P value obtained for alertness was 0.594. Hence, there is
no significant difference in how alert the participants felt
between the intervention group and control group before
consumption of the drinks.
The mean score of how awake the participants felt in the
intervention group (energy drinks) was 6.77 (out of 10) with
a SD of 2.01, while in the control group, the mean was 6.23
with a SD of 1.88. The mean difference (95% CI) and tstatistics of wakefulness between the intervention group and
control group was 0.54 (-0.55, 1.62) and 1 respectively. The
P value obtained for wakefulness was 0.305. Hence, this
indicates that there is no significant difference in the how
American Journal of Food Science and Health Vol. 5, No. 3, 2019, pp. 126-141 134
awake the participants felt between the intervention and
control group before consumption of the drinks.
The mean score of how energetic the participants felt in the
intervention group (energy drinks) was 6.15 (out of 10) with
a SD of 1.89, while in the control group, the mean was 5.58
with a SD of 2.12. The mean difference (95% CI) and tstatistics of how energetic the participants felt between the
intervention group and control group was 0.58 (-0.54, 1.70)
and 1.04 respectively. The P value obtained was 0.305.
Hence, there is no significant difference in how energetic the
participants felt between the intervention group and control
group before the intervention.
The mean score of participants’ anxiety level in the
intervention group (energy drinks) was 4.00 (out of 10) with
a SD of 2.61, while in the control group, the mean was 3.15
with a SD of 2.11. The mean difference (95% CI) and tstatistics of anxiety levels between the intervention group and
control group was 0.85 (-0.48, 2.17) and 1.29 respectively.
The P value obtained for the anxiety level was 0.204. This
suggests that there is no significant difference in the anxiety
levels between the intervention group and control group
before consumption of the drinks.
Table 4. Comparison of simple reaction time, short term memory, selective attention, alertness and anxiety between intervention group (energy drink) and
control group (non-caffeinated carbonated beverage) after intervention.
Outcome variables Mean (SD) Mean difference (95%CI) t-statistics (df) P-value Intervention group (n=26) Control group (n=26)
Cognitive
performance
Reaction time (ms) 266.46 (64.50) 294.19 (49.95) -27.73 (-59.87, 4.40) -1.73 (50) 0.089
Numerical memory (score) 10.15 (1.46) 9.46 (1.10) 0.69 (-0.03, 1.41) 1.93 (50) 0.060
Verbal memory (score) 44.88 (29.06) 38.23 (21.71) 6.65 (-7.64, 20.94) 0.94 (50) 0.354
Visual memory (score) 9.81 (1.74) 9.77 (1.73) 0.03 (-0.93, 1.01) 0.08 (50) 0.937
Selective attention (score) 30.27 (2.63) 29.81 (3.51) 0.46 (-1.27, 2.19) 0.54 (50) 0.594
Alertness
& anxiety
Alert (scale) 8.23 (1.21) 6.42 (1.98) 1.81 (0.89, 2.72) 3.97 (50) <0.001
Awake (scale) 8.27 (1.19) 6.46 (1.86) 1.81 (0.94, 2.67) 4.18 (50) <0.001
Energetic (scale) 8.27 (1.22) 6.04 (2.58) 2.23 (1.11, 3.36) 3.98 (50) <0.001
Anxious (scale) 5.42 (2.89) 3.81 (2.93) 1.61 (-0.003, 3.235) 2 (50) 0.051
bUnpaired t-test.
Table 4 shows the comparison of simple reaction time, short
term memory, selective attention, alertness and anxiety between
the intervention group (energy drinks) and control group (noncaffeinated carbonated beverages) after the intervention.
The mean of the participants’ reaction time in the
intervention group (energy drinks) was 266.46ms with
standard deviation (SD) of 64.50, while in the control group,
the mean was 294.19ms with SD of 49.95. The mean
difference (95% CI) and t-statistics of reaction time between
the intervention group and control group were -27.73 (-59.87,
4.40) and -1.73 respectively. The P value obtained for
reaction time is 0.089. Hence, there is no significant
difference in the reaction time between the intervention
group and control group after the consumption of the drinks.
The mean of the participants’ numerical memory score in the
intervention group (energy drink) was 10.15 with a SD of
1.46, while in the control group, the mean was 9.46 with a
SD of 1.10. The mean difference (95% CI) and t-statistics of
the numerical memory score between the intervention group
and control group was 0.69 (-0.03, 1.41) and 1.93
respectively. The P value computed for numerical memory
was 0.060. Hence, there is no significant difference in the
numerical memory between the two groups after
consumption of the drinks.
The mean of the participants’ verbal memory score in the
intervention group (energy drinks) was 44.88 with a SD of
29.06, while in the control group, the mean was 38.23 with a
SD of 21.71. The mean difference (95% CI) and t-statistics of
verbal memory score between the intervention group and
control group was 6.65 (-7.64, 20.94) and 0.94 respectively.
The P value computed for verbal memory was 0.354, which
suggested that there is no significant difference in the verbal
memory between the intervention group and control group
after the intervention ended.
The mean of the participants’ visual memory score in the
intervention group (energy drink) was 9.81 with a SD of 1.74,
while in the control group, the mean was 9.77 with a SD of
1.73. The mean difference (95% CI) and t-statistics of the
visual memory score between the intervention group and
control group was 0.04 (-0.93, 1.01) and 0.08 respectively.
The P value obtained for visual memory was 0.937, which
suggested that there is no significant difference in the visual
memory between the intervention group and control group
after consumption of the drinks.
The mean of the participants’ selective attention score in the
intervention group (energy drinks) was 30.27 with SD of
2.63, while in the control group, the mean was 29.81 with SD
of 3.51. The mean difference (95% CI) and t-statistics of the
selective attention score between the intervention group and
control group was 0.46 (-1.27, 2.19) and 0.54 respectively.
The P value gained for selective attention score was 0.594.
Thus, there is no significant difference in the selective
attention score between the intervention group and control
135 Raehan Hemanth et al.: The Effect of Energy Drinks on the Cognitive Function in Medical Students:
Randomised Controlled Trial
group after the intervention.
The mean score of the participants’ level of alertness in the
intervention group (energy drink) was 8.23 (out of 10) with a
SD of 1.21, while in the control group, the mean was 6.42
with a SD of 1.98. The mean difference (95% CI) and tstatistics of alertness between the intervention group and
control group was 1.81 (0.89, 2.27) and 3.97 respectively.
The P value obtained for alertness was <0.001. Hence, there
is a significant difference in how alert the participants felt
between the intervention group and control group after
consumption of the drinks.
The mean score of how awake the participants felt in the
intervention group (energy drinks) was 8.27 (out of 10) with
a SD of 1.19, while in the control group, the mean was 6.46
with a SD of 1.86. The mean difference (95% CI) and tstatistics of wakefulness between the intervention group and
control group was 1.81 (0.94, 2.67) and 4.18 respectively.
The P value obtained for wakefulness was <0.001. Hence,
this indicates that there is a significant difference in the how
awake the participants felt between the intervention and
control group after consumption of the drinks.
The mean score of how energetic the participants felt in the
intervention group (energy drinks) was 8.27 (out of 10) with
a SD of 1.22, while in the control group, the mean was 6.04
with a SD of 2.58. The mean difference (95% CI) and tstatistics of how energetic the participants felt between the
intervention group and control group was 2.23 (1.11, 3.36)
and 3.98 respectively. The P value obtained was <0.001.
Hence, there is a significant difference in how energetic the
participants felt between the intervention group and control
group after the intervention.
The mean score of participants’ anxiety level in the
intervention group (energy drinks) was 5.42 (out of 10) with
a SD of 2.89, while in the control group, the mean was 3.81
with a SD of 2.93. The mean difference (95% CI) and tstatistics of anxiety levels between the intervention group and
control group was 1.615 (-0.003, 3.235) and 2 respectively.
The P value obtained for the anxiety level was 0.051. This
suggests that there is no significant difference in the anxiety
levels between the intervention group and control group after
consumption of the drinks.
Table 5. Comparison of simple reaction time, short term memory, selective attention, alertness and anxiety in the intervention group (energy drink) before and
after consuming the energy drink.
Outcome variables Mean (SD) (n=26) Mean difference (95%CI) t-statistics (df) P-value Before After
Cognitive
performance
Reaction time (ms) 296.96 (53.66) 266.46 (64.50) 30.50 (5.20, 55.80) 2.48 (25) 0.020
Numerical memory (score) 10.31 (1.83) 10.15 (1.46) 0.15 (-0.41, 0.72) 0.56 (25) 0.582
Verbal memory (Score) 33.69 (24.20) 44.88 (29.06) -11.19 (-22.46, 0.07) 2.05 (25) 0.051
Visual memory (score) 9.69 (2.68) 9.81 (1.74) -0.12 (-0.99, 0.76) 0.27 (25) 0.424
Selective attention (score) 26.62 (8.20) 30.27 (2.63) -3.65 (-6.75, -0.55) 2.42 (25) 0.023
Alertness
& anxiety
Alert (scale) 6.62 (1.88) 8.23 (1.21) -1.62 (-2.18, -1.05) 5.94 (25) <0.001
Awake (scale) 6.77 (2.01) 8.27 (1.19) -1.50 (-2.17, -0.83) 4.62 (25) <0.001
Energetic (scale) 6.15 (1.89) 8.27 (1.22) -2.12 (-2.74, -1.49) 6.93 (25) <0.001
Anxious (scale) 4.00 (2.61) 5.81 (1.39) -1.81 (-3.12, -0.50) 2.84 (25) 0.010
c
Paired t-test.
Table 5 shows the comparison of reaction time, numerical
memory, verbal memory, visual memory, selective attention,
alertness, and how awake, energetic and anxious the
participants felt before and after consuming the energy drinks.
The mean (SD) of the reaction time before and after
consumption of the energy drinks was 296.96ms (53.66) and
266.46ms (64.50) respectively. The mean difference (95% CI)
and t-statistics of reaction time calculated before and after
consumption was 30.50 (5.20, 55.80) and 2.48 respectively.
There was a decrease of reaction time after the drinks were
consumed with the magnitude of 30.50 mean difference. The
P value of reaction time computed was 0.020. Hence, there is
significant difference in the reaction time of the participants
before and after the intervention.
The mean (SD) of the numerical memory before and after
consumption of the energy drinks was 10.31 (1.83) and 10.15
(1.46) respectively. The mean difference (95% CI) and tstatistics of numerical memory calculated before and after the
drinks were consumed was 0.15 (-0.41, 0.72) and 0.56
respectively. There was a decrease of numerical memory
after drinking the energy drink with the magnitude of 0.15
mean difference. The P value of numerical memory
computed was 0.582. Hence, there is no significant difference
in the numerical memory of the participants before and after
drinking the energy drinks.
The mean (SD) of the verbal memory before and after
consumption of the drink was 33.69 (24.20) and 44.88 (29.06)
respectively. The mean difference (95% CI) and t-statistics of
verbal memory calculated before and after consumption was
-11.19 (-22.46, 0.07) and 2.05 respectively. There was an
increase of verbal memory after consuming the energy drinks
with the magnitude of -11.19 mean difference. The P value of
verbal memory computed was 0.051. Hence, there is no
American Journal of Food Science and Health Vol. 5, No. 3, 2019, pp. 126-141 136
significant difference in the verbal memory of the
participants before and after energy drink consumption.
The mean (SD) of the visual memory before and after
consumption of the intervention drink was 9.69 (2.68) and
9.81 (1.74) respectively. The mean difference (95% CI) and tstatistics of visual memory calculated before and after the
intervention was -0.12 (-0.99, 0.76) and 0.27 respectively.
There was an increase of visual memory after energy drink
consumption with the magnitude of -0.12 mean difference.
The P value of visual memory computed was 0.424. Hence,
there is no significant difference in the visual memory of the
participants before and after the intervention.
The mean (SD) of the selective attention before and after the
intervention was 26.62 (8.20) and 30.27 (2.63) respectively.
The mean difference (95% CI) and t-statistics of selective
attention calculated before and after the intervention was –
3.65 (-6.75, -0.55) and 2.42 respectively. There was an
increase of selective attention after consumption of the
energy drinks with the magnitude of -3.65 mean difference.
The P value of selective attention computed was 0.023.
Hence, there is a significant difference in the selective
attention of the participants before and after the intervention.
The mean (SD) of the alert before and after the intervention
was 6.62 (1.88) and 8.23 (1.21) respectively. The mean
difference (95% CI) and t-statistics of alertness calculated
before and after intervention was -1.62 (-2.18, -1.05) and
5.94 respectively. There was an increase in alertness after
energy drink consumption with the magnitude of -1.62 mean
difference. The P value of alert computed was <0.001. Hence,
there is a significant difference in the levels of alertness of
the participants before and after the intervention.
The mean (SD) of how awake the participants felt before and
after the intervention was 6.77 (2.01) and 8.27 (1.19)
respectively. The mean difference (95% CI) and t-statistics of
how awake they felt calculated before and after energy drink
consumption was -1.50 (-2.17, -0.83) and 4.62 respectively.
There was an increase of how awake they felt after
consuming the energy drinks with the magnitude of -1.50
mean difference. The P value of awake computed was <0.001.
Hence, there is a significant difference in how awake the
participants felt before the after the intervention.
The mean (SD) of the energetic levels before and after
energy drink consumption was 6.15 (1.89) and 8.27 (1.22)
respectively. The mean difference (95% CI) and t-statistics of
the energetic levels calculated before and after the
intervention was -2.12 (-2.74, -1.49) and 6.93 respectively.
There was an increase of how energetic the participants felt
after consuming the energy drinks with the magnitude of –
2.12 mean difference. The P value of energetic computed was
<0.001. Hence, there is a significant difference in the
energetic levels of the participants before the after the
intervention.
The mean (SD) of the anxiety levels before and after the
intervention was 4.00 (2.61) and 5.81 (1.39) respectively. The
mean difference (95% CI) and t-statistics of the anxiety
levels calculated before and after energy drink consumption
was -1.81 (-3.12, -0.50) and 2.84 respectively. There was an
increase of anxiety felt by the participants after consuming
the energy drinks with the magnitude of -1.81 mean
difference. The P value of anxious computed was 0.010.
Hence, there is a significant difference in the anxiety levels
of the participants before and after treatment.
Table 6. Comparison of simple reaction time, short term memory, selective attention, alertness and anxiety in the control group (non-caffeinated carbonated
beverage) before and after consuming the non-caffeinated carbonated beverage.
Outcome variables Mean (SD) (n=26) Mean difference (95%CI) t-statistics (df) P-value Before After
Cognitive
performance
Reaction time (ms) 331.00 (100.81) 294.19 (49.95) 36.81 (-0.51, 74.12) 2.03 (25) 0.053
Numerical memory (score) 9.00 (1.67) 9.46 (1.10) -0.46 (-1.24, 0.32) 1.22 (25) 0.233
Verbal memory (Score) 35.65 (26.36) 38.23 (21.72) -2.58 (-13.62, 8.47) 0.48 (25) 0.635
Visual memory (score) 9.04 (1.66) 9.77 (1.73) -0.73 (-1.32, -0.14) 2.56 (25) 0.017
Selective attention (score) 28.46 (4.94) 29.81 (3.51) -1.35 (-3.53, 0.84) 0.22 (25) 0.217
Alertness
& anxiety
Alert (scale) 6.35 (1.74) 6.42 (1.98) -0.08 (-0.82, 0.66) 0.21 (25) 0.832
Awake (scale) 6.23 (1.88) 6.46 (1.86) -0.23 (-0.83, 0.37) 0.80 (25) 0.434
Energetic (scale) 5.58 (2.12) 6.04 (2.58) -0.46 (-1.20, 0.28) 1.28 (25) 0.212
Anxious (scale) 3.15 (2.11) 3.81 (2.93) -0.65 (-1.51, 0.20) 1.58 (25) 0.128
c
Paired t-test.
Table 6 shows the comparison of reaction time, numerical
memory, verbal memory, visual memory, selective attention,
alertness, and how awake, energetic and anxious the
participants feel before and after drinking the control drink.
The mean (SD) of the reaction time before and after the
intervention was 331.00ms (100.81) and 294.19ms (49.95)
respectively. The mean difference (95% CI) and t-statistics of
the reaction time calculated before and after the intervention
was 36.81 (-0.51, 74.12) and 2.03 respectively. There was a
decrease of reaction time after control drink consumption
with the magnitude of 36.81 mean difference. The P value of
reaction time computed was 0.053. Hence, there is no
significant difference in the reaction time of the participants
137 Raehan Hemanth et al.: The Effect of Energy Drinks on the Cognitive Function in Medical Students:
Randomised Controlled Trial
before and after consuming the control drink.
The mean (SD) of the numerical memory before and after the
intervention was 9.00 (1.67) and9.46 (1.10) respectively. The
mean difference (95% CI) and t-statistics of numerical
memory calculated before and after the intervention was-0.46
(-1.24, 0.32) and 1.22 respectively. There was an increase in
numerical memory after consumption of the control drink
with the magnitude of -0.46 mean difference. The P value of
numerical memory computed was 0.233. Hence, there is no
significant difference in the numerical memory of the
participants before and after the intervention.
The mean (SD) of the verbal memory before and after the
intervention was 35.65 (26.36) and 38.23 (21.72) respectively.
The mean difference (95% CI) and t-statistics of verbal
memory calculated before and after the intervention was –
2.58 (-13.62, 8.47) and 0.48 respectively. There was an
increase of verbal memory after control drink consumption
with the magnitude of -2.58 mean difference. The P value of
verbal memory computed was 0.635. Hence, there is no
significant difference in the verbal memory of the
participants before and after the intervention.
The mean (SD) of the visual memory before and after the
intervention was 9.04 (1.66) and 9.77 (1.73) respectively. The
mean difference (95% CI) and t-statistics of visual memory
calculated before and after the intervention was-0.73 (-1.32, –
0.14) and 2.56 respectively. There was an increase of visual
memory after consumption of the control drink with the
magnitude of -0.73 mean difference. The P value of visual
memory computed was 0.017. Hence, there is a significant
difference in the visual memory of the participants before and
after the intervention.
The mean (SD) of the selective attention before and after the
intervention was 28.46 (4.94) and 29.81 (3.51) respectively.
The mean difference (95% CI) and t-statistics of selective
attention calculated before and after the intervention was –
1.35 (-3.53, 0.84) and 0.22 respectively. There was an
increase of selective attention after consumption of the
control drink with the magnitude of -1.35 mean difference.
The P value of selective attention computed was 0.217.
Hence, there is no significant difference in the selective
attention of the participants before and after the intervention.
The mean (SD) of the alertness before and after the
intervention was 6.35 (1.74) and 6.42 (1.98) respectively. The
mean difference (95% CI) and t-statistics of alertness
calculated before and after the intervention was -0.08 (-0.82,
0.66) and 0.21 respectively. There was an increase of alert
after drinking the control drink with the magnitude of -0.08
mean difference. The P value of alert computed was 0.832.
Hence, there is no significant difference in the alertness of
the participants before and after the intervention.
The mean (SD) of how awake the participants felt before and
after the intervention was 6.23 (1.88) and 6.46 (1.86)
respectively. The mean difference (95% CI) and t-statistics of
awake calculated before and after the intervention was -0.23
(-0.83, 0.37) and 0.80 respectively. There was an increase of
how awake they felt after drinking the control drink with the
magnitude of -0.23 mean difference. The P value of how
awake they felt computed was 0.434. Hence, there is no
significant difference in how awake the participants felt
before and after the intervention.
The mean (SD) of the energetic levels before and after the
intervention was 5.58 (2.12) and 6.04 (2.58) respectively. The
mean difference (95% CI) and t-statistics of energetic
calculated before and after the intervention was -0.46 (-1.20,
0.28) and 1.28 respectively. There was an increase in the
energy levels after drinking the control drink with the
magnitude of -0.46 mean difference. The P value of energetic
levels computed was 0.212. Hence, there is no significant
difference in the energetic levels of the participants before
and after the intervention.
The mean (SD) of the anxiety levels before and after the
intervention was 3.15 (2.11) and 3.81 (2.93) respectively. The
mean difference (95% CI) and t-statistics of anxious calculated
before and after the intervention was -0.65 (-1.51, 0.20) and
1.58 respectively. There was an increase in anxiety felt after
consuming the control drinks with the magnitude of -0.65
mean difference. The P value of anxiety levels computed was
0.128. Hence, there is no significant difference in the anxiety
levels of the participants before and after the intervention.
Table 7. Comparison of adverse effects experienced by participants 30 minutes after consuming the beverage and insomnia between intervention (energy drink)
group (n=26) and control (non-caffeinated carbonated beverage) group (n=26) after intervention.
Variable (Adverse effects) Intervention group n (%) Control group n (%) RR (95%CI) x
2 P-value Yes No Yes No
Palpitations 9 (34.62) 17 (65.38) 3 (11.54) 23 (88.46) 3 (0.91, 9.84) 3.9 0.048d
Tremors/shaking handse 4 (15.18) 22 (84.62) 5 (19.23) 21 (80.77) 0.8 (0.24, 2.65) – 0.999
Restlessnesse 6 (23.08) 20 (76.92) 3 (11.54) 23 (88.46) 2 (0.56, 7.15) – 0.465
Dizzinesse 0 (0) 26 (100) 3 (11.54) 23 (88.46) Undefined – 0.235
Syncope 0 (0) 26 (100) 0 (0) 26 (100) – – –
Stomach-achee 1 (3.85) 25 (96.15) 1 (3.85) 25 (96.15) 1 (0.07, 15.15) – 0.999
Paraesthesia (tingling or numbness of skin) 0 (0) 26 (100) 0 (0) 26 (100) – – –
Headachee 2 (7.69) 24 (92.31) 3 (11.54) 23 (88.46) 0.67 (0.12, 3.67) – 0.999
American Journal of Food Science and Health Vol. 5, No. 3, 2019, pp. 126-141 138
Variable (Adverse effects) Intervention group n (%) Control group n (%) RR (95%CI) x
2 P-value Yes No Yes No
Dehydratione 2 (7.69) 24 (92.31) 2 (7.69) 24 (92.31) 1 (0.15, 6.57) – 0.999
Increased urinatione 4 (15.38) 22 (84.62) 4 (15.38) 22 (84.62) 1 (0.28, 3.58) – 0.999
Nauseae 0 (0) 26 (100) 1 (3.85) 25 (96.15) Undefined – 0.999
Chest pain 0 (0) 26 (100) 0 (0) 26 (100) – – –
Insomniae 4 (15.38) 22 (84.62) 1 (3.85) 25 (96.15) 4 (0.48, 33.42) – 0.350
dChi-square e
Fisher exact.
Table 7 shows the adverse effects experienced by participants
in the intervention group (energy drink) 30 to 60 minutes
after consuming the beverage and insomnia in comparison to
the control group (non-caffeinated carbonated beverage).
Participants who drank the energy drink are 3 times more
likely to experienced palpitations compared to those who
drank the control drink (non-caffeinated carbonated
beverage). The P value obtained and Chi square value were
0.048 and 3.9 respectively. However, according to relative
risk (95% CI), the value obtained was 3 (0.91, 9.84). Hence,
there is no statistically significant difference in the
participants having palpitations after consuming energy drink
compared to the control group.
Participants who consumed energy drink are less likely to
have tremors compared to those who drank the control drink.
The P value obtained by Fisher exact test was 0.999.
According to relative risk (95% CI), the value obtained was
0.8 (0.24, 2.65). Hence, there is no statistically significant
difference in the participants having tremors after consuming
the energy drink compared to the control group.
Participants who consumed energy drinks are 2 times more
likely to experienced restlessness compared to those who
drank the control drink. The P value obtained by Fisher exact
test was 0.465. According to relative risk (95% CI), the value
obtained was 2 (0.56, 7.15). Hence, there is no statistically
significant difference in the participants being restless after
consuming energy drinks compared to the control group.
11.54% of the participants who drank the control drink have
dizziness whereas 0% of participants who consumed the
energy drink developed dizziness. The P value obtained by
Fisher exact test was 0.235. Hence, there is no significant
difference in the participants having dizziness after
consuming energy drinks compared to the control group.
There is no association between stomach-ache and
consumption of energy drink as 3.85% of the participants
from both the intervention and control groups respectively
developed stomach-ache. The P value obtained by Fisher
exact test was 0.999. According to relative risk (95% CI), the
value obtained was 1 (0.07, 15.15). Hence, there is no
statistically significant difference in the participants having
stomach-ache after consuming energy drinks compared to the
control group.
Participants who consumed energy drink are less likely to
experienced headaches compared to those who drank the
control drink. The P value obtained by Fisher exact test was
0.999. According to relative risk (95% CI), the value
obtained was 0.67 (0.12, 3.67). Hence, there is no statistically
significant difference in the participants having headache
after consuming energy drinks compared to the control group.
There is no association between dehydration and
consumption of energy drink as 7.69% of the participants
from both intervention and control groups respectively felt
dehydrated. The P value obtained by Fisher exact test was
0.999. According to relative risk (95% CI), the value
obtained was 1 (0.15, 6.57). Hence, there is no statistically
significant difference in the participants feeling dehydrated
after consuming energy drinks compared to the control group.
There is no association between increased urination and
consumption of energy drink as 15.38% of the participant
from both intervention and control groups respectively have
increased urination. The P value obtained by Fisher exact test
was 0.999. According to relative risk (95% CI), the value
obtained was 1 (0.28, 3.58). Hence, there is no statistically
significant difference in the participants having increased
urination after consuming energy drinks compared to the
control group.
3.85% of the participants who drank the control drink have
nausea whereas 0% of the participants who consumed the
energy drink developed nausea. The P value obtained by
Fisher exact test was 0.999. Hence, there is no significant
difference in the participants having nausea after consuming
energy drinks compared to the control group
Participants who consumed energy drink are 4 times more likely
to have insomnia compared to those who drank the control drink.
The P value obtained by Fisher exact test was 0.350. According
to relative risk (95% CI), the value obtained was 4 (0.48, 33.42).
Hence, there is no statistically significant difference in the
participants having insomnia after consuming energy drinks
compared to the control group.
4. Discussion
The purpose of this randomised controlled trial was to
determine the effects of energy drink consumption on the
139 Raehan Hemanth et al.: The Effect of Energy Drinks on the Cognitive Function in Medical Students:
Randomised Controlled Trial
cognitive performance of medical students, namely the
reaction time, selective attention, short term memory in terms
of numerical, verbal and visual, and to determine the
immediate adverse effects. A total of 52 medical students
were randomised into an intervention group (26 students) to
whom we gave an energy drink and a control group (26
students) to whom we gave a non-caffeinated carbonated
beverage.
Based on our study, although the results suggested that the
intervention group performed better on the cognitive
performance tests such as reaction time, numerical memory,
verbal memory, visual memory and selective attention than
those who were in the control group, we found that there was
no significant difference between the two groups. The results
were consistent with a study done in Columbia, where the
results obtained from consuming energy drinks showed no
significant difference in immediate memory and
concentration as compared to the placebo drinks [28]. This is
further supported by Warburton et al. who found no
significant improvement in memory between caffeinated
taurine drinks and the placebo drink as well [11]. However,
these findings contradicted with one study which found a
significant improvement in reaction time, concentration and
memory after consumption of energy drinks [13].
On the other hand, regarding alertness and anxiety, the
intervention group demonstrated increased alertness, but they
noted to experience higher levels of anxiety than those who
were in the control group. The results for alertness showed
that there was a significant difference among the two groups.
The findings corresponded with a study carried out in United
Kingdom which found an increase in subjective alertness in
the energy drink group [13]. However, there was no
significant difference between the intervention group and
control group in terms of their anxiety levels. This was
supported by a study carried out in Tunisia which found that
there was no significant difference for anxiety levels in the
participants who consumed either energy drinks or the
placebo drink [29].
The comparison of cognitive performance in the intervention
group before and after consuming the drinks showed that
they had increased reaction time and better selective attention,
which is of statistically significant difference. However,
numerical, verbal and visual memory indicated no significant
difference. The improved performance in reaction time and
attention goes along with the study conducted by Scholey et
al. [12]. The intervention group showed to be more anxious
post-intervention, although they indicated that they felt more
alert, awake and energetic which is of significant difference.
The improvement in alertness was justified by Hendrik et al.
who found significant improvements on task performance
and self-assessed mood after consuming energy drinks as the
participants in this group felt more alert, revitalised and
awakened [30]. Moreover, Stasio et al. found that energy
drink consumption had a positive effect on anxiety scores
and sleep disturbances [31].
The participants were required to fill in a questionnaire
regarding any side effects they encountered after consuming the
drinks. The main side effects enquired about were palpitations,
tremors, restlessness, dizziness, syncope, stomach-ache,
paraesthesia, headache, dehydration, increased urination, nausea,
chest pain and insomnia, out of which syncope, paraesthesia and
chest pain were not experienced by any of the participants, thus
indicating these outcomes were of no significant difference
regarding consumption of energy drinks in this present study.
Occurrence of palpitations, restlessness and insomnia were more
common among the intervention group whereas tremors,
dizziness, headache and nausea were more common among the
control group. The occurrence of stomach-ache, dehydration and
increased urination were equivalent between the two groups,
thus indicating no significant difference between these adverse
effects and intake of the drinks. Overall, in this present study,
there was no significant difference between the adverse effects
and the consumption of beverages. This is supported by similar
studies as no immediate side effects were reported by the
participants after drinking these beverages [28, 29]. However,
energy drinks have been associated with caffeine overdose
resulting in insomnia, restlessness, tachycardia and even fatality
[2].
The response rate was 100% with no drop-outs in between
the study. However, we have a few limitations. As this study
was conducted among healthy undergraduate medical
students of young adult age, the findings cannot be
generalised to larger demographic population. Furthermore, it
is not possible to identify the specific active ingredients in
energy drinks that contribute to the improvement in certain
cognitive performance. Glucose, an ingredient present in
both drinks, could have possibly contributed to the outcome
of the cognitive performance however. Another limitation is
not all the confounding variables could be controlled such as
duration of sleep and amount of exercise carried out a day
before the study was conducted. Participants might have been
familiar with the way the cognitive performance was being
assessed as the cognitive function tests were evaluated twice,
once before and after consuming the drinks. Therefore, the
improvement in cognitive performance may have been due to
practice. In addition, blinding was not included in our
randomised controlled trial and this might have led to bias as
the participants could identify the drink that they were
consuming, thus influencing or eliminating the subjectivity
assessed such as alertness and anxiety level.
Further experiments may consider assessing the active
ingredient of energy drinks individually which may enhance
American Journal of Food Science and Health Vol. 5, No. 3, 2019, pp. 126-141 140
cognitive performance. Adverse effects of energy drinks
among regular energy drink consumers can be investigated
more deliberately. Further studies may consider using a
blinding design to avoid occurrence of bias as well as
obtaining a larger sample size.
5. Conclusion
Consumption of energy drinks has been a weekly routine in
many teenagers and young adults as the beverages are easily
accessible. Evident improvement in the reaction time,
selective attention and alertness among the intervention
group after consumption of the energy drinks in comparison
to their performance prior to the intake of the beverage have
been demonstrated in our present study. However, according
to our study results, energy drink intake has shown no
beneficial effect on short term memory. The levels of
alertness is enhanced significantly among the participants
who consume energy drinks compared to the control group
(non-caffeinated carbonated beverages). Furthermore, there
was no significant difference in immediate adverse effects
between the intervention and control groups.
Acknowledgements
First and foremost, we would like to give a big thanks to all the
students who voluntarily participated in this study. We would
like to express our deepest appreciation to the Dean and Head of
department, Professor Dr. Adinegara Lutfi Abbas, Professor Dr.
Htoo Htoo Kyaw Soe and Associate Professor Dr. Sujata
Khobragade from the Department of Community Medicine of
Melaka Manipal Medical College for helping us throughout the
research. Lastly, we would like to thank the Research Ethics
committee for approving our study.
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