Caffeine, a methylxanthine, is the most widely used psycho-active drug and is an antagonist of adenosine receptors, particularly the a1 and a2a adenosine subtypes [1; 2]. This accounts for caffeine’s stimulatory properties. This dietary component has been the subject of extensive research, primarily due to its widespread use in dietary products such as the commercial energy drink, Red Bull. Most of the beverages known as energy drinks consist of a combination of carbohydrates (approx 11mg/dl), taurine (approx 400mg/dl), caffeine (about 32mg/dl) gluconalactone (approx 240mg/dl) and vitamin B complex, [3], however the active ingredients of which are primarily appreciated to be caffeine and taurine [4].
Taurine, a naturally occurring amino acid, has not been extensively
investigated in relation to energy drinks. It is, however, widely
appreciated to play an important role in neuroprotection and
enhancement of neurotransmission, [8]. Taurine is also found at high
levels in skeletal muscles, and appears to modulate contractile
function, It is thought to enhance accumulation and release of
sarcoplasmic reticulum Ca2+, thus increasing force generation within
muscles [9]. This could explain the findings of Huxtable et al. [10],
of depleted taurine stores, when the body is under extreme stress such
as physical exercise, whilst otherwise, there is high conserved taurine
stores in the human body under normal physiological conditions. Other
studies show that taurine has cytoprotective, anti-oxidative properties
[11].
The literature pertaining to taurine with respect to its role in energy
drinks, have addressed the combined effects of caffeinated and taurine
beverages found Red Bull to influence cardiac contractility [12; 13;
14; 15]. Results reported significant increases in stroke volume and
diastolic inflow velocity, thus enhancing ventricular function;
however, the beneficial effects of taurine supplementation upon the
heart have been described in healthy hearts as well as failing heart,
[15;16].
Studies with energy drinks, yield results in many indices similar to
those already found with caffeine alone, although caffeine as an
ingredient is deemed active within energy drinks, other active
ingredients like taurine have not been studied in isolation.
As the individual role of taurine has not been established, the aim of
this present study is to address the question of taurine’s role in
energy drinks, in its purest form without the verum constituents. The
question of whether taurine has effects on EEG, systolic or diastolic
blood pressure (BP), heart rate and reaction time will be investigated.
Results may find taurine to have no significant effect when
administered alone; hence, caffeine and taurine may act in synergy with
one another, or even modulate the role of caffeine. This study also
aims to substantiate caffeine’s effects on cardiovascular activity.
2 Materials and methods
2.1 Subjects
Twenty-four young, healthy subjects, both men and
women aged 19-22 years volunteered to participate in the study.
Subjects were given information about the study prior to participation.
Health questionnaires and written informed consent was completed by all
subjects.
2.2 Study Design
The volunteers refrained from caffeine and
caffeine-containing products for twelve hours before the study. The
study was conducted within a six-week period. The test design was
planned as double blind for one experimenter where both the
investigator and volunteer was unaware of the solution consumed. The
second experimenter knew the solution being administered, however the
volunteer did not, i.e. the test was single blind.
The administered drinks were the same in colour and volume. The
solutions had the following compositions: Solution A: Control (250ml
orange juice); Solution B: Taurine (2 x 500mg tablets + 250ml orange
juice); Solution C: Caffeine (80mg ProPlus tablet + 250ml orange
juice). In practice, the trial was designed in four different sections:
control, exercise, solution, post solution and exercise. Each section
had a duration of 30min. Vigorous exercise portions lasted for two
minutes in total.
2.2.1 Solution preparation
The same brand of orange juice was
used for each test. The caffeine and taurine amounts are those
typically found in one serving of Red Bull. ProPlus tablets were
crushed, centrifuged for 1min and allowed to settle for 2hours before
consumption. Taurine was administered orally in tablet form. Each
solution was consumed within a 1 min period and subjects were advised
to consume a meal prior to beginning the trial to offset possible
nausea.
2.3 Measurements
All measurements were made with the volunteer in a seated position. Specific times were allocated for each measurement criteria.
2.3.1 ECG recordings
ECG recordings were used to measure heart
rate, using standard Bipolar ECG leads and utilising the PowerLab
computer system. ECG recordings were taken for each participant as soon
as the trail began. It was a precautionary measure, required by the
ethics committee, in order to trace heart murmurs, or irregular heart
readings. Regular ECG recording using the bi-polar limb leads on the
PowerLab system.
2.3.2 EEG measurements
The EEG was measured twice in the trial:
once at rest and once after the solution was taken. EEG measurements
were performed by attaching electrodes at particular positions on the
scalp using the Electro-Cap system (which comprises a skull cap
incorporating an array of electrodes). In order to measure EEG, the
scalp is first gently scratched to enable a good electrical contact to
be made when attaching the electrodes (an electrolyte gel was used to
maximise conductance).
2.3.3 Reaction time
A reaction meter, which involved pressing a
button in response to a coloured light turning on was used to measure
reaction times. The colours were randomly selected to avoid
sensitisation.
2.3.4 Blood pressure
Sphygmomanometer and cuff was used to
measure BP. Basal measurements of systolic and diastolic arterial BP
were made at rest, with the subject in a seated position. Systolic and
diastolic BP was determined by auscultation, using a sphygmomanometer,
after solution and before and after exercise.
2.3.5 Heart rate
Basal heart rate (beats per minute) was
measured by palpation. This was repeated after ingestion of the
solution and also before and after exercise (using an exercise bike
with heart rate monitor).
2.4 Protocol
The ECG was the first measurement made in order to
determine whether the participant was eligible to continue. Basal
measurements of heart rate and systemic and diastolic arterial BP were
made at rest, with the subject in a seated position. EEG and reaction
times were also measured as described. These were taken as the control
readings.
The subject was then asked to perform vigorous exercise for 2 min,
using an exercise bike (pulse rate did not exceed 180/min). This
exercise was followed by further measurements (as above) at regular
intervals for 30 minutes. The subjects were then given the test
solution. Fifteen minutes of rest followed in order to allow sufficient
time for the caffeine or taurine to be absorbed. The measurements were
then repeated for a period of 30 min and, for all subjects, all
measurements began at time 0 and took the following repetitions: Heart
rate via palpitation was taken every 3 min; BP every 10 min; ECG every
15 min; EEG was taken 45 minutes after solution and also in the control
period of rest; and reaction times were taken at the 17th minute of
each 30 min segment.
For each of the four sections in the trial, standardized measurements
were taken at the same intervals, for each 30 minute segment.
2.5 Ethics
The experimental protocol was approved by the
University of Manchester’s ethics committee for research on human
beings. All procedures were conducted safely.
2.6 Statistical analysis.
A two-way ANOVA test was applied to
the data to determine whether each variable had an effect and whether
the variables interacted with each other. Statistical significance was
set at P<0.05.
3 Results and Discussion
3.1 Effects on blood pressure
As can be seen from Figure 1,
compared to the control, both experimental groups had a higher systolic
and diastolic BP throughout the experiment, except during the second
round of exercise. However, these differences were not significant
(P=___, P=___ for the caffeine and taurine groups, respectively). The
systolic BP of the control group fell more than both experimental
groups between the exercise rounds (time: 3-78min). This could be due
to the effects of the caffeine and taurine on the cardiovascular
system. It is known that caffeine elevates BP due to vascular
resistance with no change in cardiac output in men, and in women this
effect is mediated by a change in cardiac output but no change to
vascular resistance [17]. Also, if accompanied by stress, caffeine can
increase peak systolic BP to hypertensive levels [18]. In these
studies, the stress was caused by giving the subjects a task to
complete [19], much like the tasks in the present study. Taurine also
has cardiovascular effects by improving the heart rate, cardiac
function, BP and by removing oxidative stress [20]. The mechanism of
these actions has not been fully elucidated but is thought to be due to
its anti-oxidant, cytoprotective effects [11].
Each round of exercise resulted in an increase in systolic BP and
decreases in diastolic BP, which normalised to approximate resting
values after the exercise was stopped, as would be expected.
Figure 1. Graph showing the mean systolic (top) and diastolic (bottom)
blood pressures from throughout the time course of the experiment.
Time zero represents the mean heart rate at rest, time 3-33min is the
time between finishing the first 2min exercise and taking the solution,
the second round of exercise was completed between time 78-80min. The
black diamonds represents the control group, the red squares represent
the caffeine group and the yellow triangles represent the taurine
group. Error bars represent the standard error of the mean.
3.2 Effects on heart rate
Figure 2 shows the heart rates
throughout the experiment. As expected, the heart rate changed
significantly throughout the course of the experiment (P=__, P=____,
P=___ for control, caffeine and taurine, respectively). Although not
significantly different (P=____), the heart rate of the control group
was consistently greater than either the taurine group or the caffeine
group, except at the peak during the second bout of exercise after the
solutions were taken. It is known that energy drinks, or coffee, cause
a significant increase in heart rate and diastolic BP, compared to
placebo [21]. However, these effects were not observed in the present
study.
Figure 2. Graph showing the mean change in heart rate over the time
course of the experiment. Time zero represents the mean heart rate at
rest, time 3-33min is the time between finishing the first 2min
exercise and taking the solution, the second round of exercise was
completed between time 78-80min. The black diamonds represents the
control group, the red squares represent the caffeine group and the
yellow triangles represent the taurine group. Error bars represent the
standard error of the mean.
Surprisingly, the heart rate of the caffeine group lowered
significantly after taking the solution (Figure 3). After taking the
solution, the heart rate stabilised and, over the course of the 30min,
approached the mean change values observed in the control group. The
taurine group, however, experienced large mean variations in heart rate.
It can be seen that the heart rate did not reach the maximum
experienced during the first round of exercise, just after rest.
However, this is probably because the body had acclimatised to the
exercise, i.e. the body had ‘warmed up’ and was not due to the solution
taken as the three groups did not have significantly different heart
rates. Alternatively, this observed effect could be due to the
rehydrating effect of the solution taken.
Figure 3. Graph showing the mean change in heart rate after taking the test solutions.
The black diamonds represents the control group, the red squares
represent the caffeine group and the yellow triangles represent the
taurine group.
3.3 Effects on reaction times
As can be seen from Table 1,
caffeine significantly reduced the reaction times (P=____) from 0.292s
at rest, to 0.260s after taking the solution and exercise. Taurine also
reduced the reaction times (P=___) from 0.307s at rest, to 0.281s after
solution and exercise.
Subject group Rest/ s Post-ex/ s Mean change post ex/ s
Post-sol/ s Mean change post sol/ s Post-sol, post-ex Mean
change post-sol, post-ex
Control 0.359 0.335 -0.023 0.314 -0.040 0.315 -0.044
Caffeine 0.292 0.296 0.010 0.265 -0.027 0.260 -0.032
Taurine 0.307 0.299 -0.001 0.319 0.005 0.281 -0.018
Table 1. The reaction times, in seconds, of the subjects in the control
group and the groups that took either a caffeine, or taurine, solution.
Post-ex = post-exercise; post-sol = post-solution.
3.4 Effects on ECG
The ECG recordings did not show any
abnormalities either before, or during, the experiment for any of the
experimental groups. Neither the placebo, nor the solutions caused
changes to the QRST complex.
3.5 Effects on EEG
Caffeine has known stimulant effects on the
CNS and it is thought that mild cortex stimulation results in clearer
thinking and less fatigue, thereby increasing attention [22]. Evidence
of arousal has been provided by EEG studies of brain cortical areas
[2]. One study has shown that, upon treatment with caffeine, the EEG
showed more activation and a faster frequency and lower amplitude with
increased arousal (Gibbs and Maltby, 1943). There are no equivalent
studies, at present, into the possible effects of taurine.
***This section of the paper has not been completed but helpful information has been included below:***
*****Sorry, but being able to locate the origin of electrical activity
("localization") is critical to being able to interpret the EEG
tracings meaningfully.***
***insufficient data given to evaluate the results of the EEG.***
***Numbers given in excel sheet have not been labelled and units (if
any) have not been explained. Reason why two sets of numbers included
in some cells are unexplained***
***The names of the electrode sites use alphabetical abbreviations that
identify the lobe or area of the brain to which each electrode refers:
F = frontal
Fp = frontopolar
T = temporal
C = central
P = parietal
O = occipital
A = auricular (ear electrode).
***The localization of the brain waves within the brain regions or
lobes is further narrowed by adding electrodes, which are given numbers
such as T3, T4, P3, P4. Even numbers identify electrode positions on
the right side of the head, and odd numbers refer to the left side. The
label "z" points to electrode sites in the midline of the head. For
example, Cz refers to the midline central region of the head.***
3.6 Limitations of the study
The factors which cause this study
to be of limited value are that different people were used in the
different groups and that a low number of subjects (8) were used for
each group. This means that significant variation could have been
introduced through the use of different people; if the same subjects
were used for each test group then the effect of the test solution
could more easily be noticed. The lack of subject numbers and
replicates means that the results of this experiment cannot be
conclusively and generally applied. Also, as the dietary intake of each
subject before the experiment started was not controlled or recorded,
it cannot be ruled out that this may have affected the results.
3.7 Conclusions
As expected, the heart rate and blood pressures
changed significantly throughout the course of the experiment. However,
there were no significant differences in the heart rate and either of
the blood pressure measurements between the control and the test
groups. Reaction times, however, were improved in the group that took
the caffeine solution. Taurine was found to have no significant effects
in these experiments. However, as the effect of caffeine was also not
pronounced, no conclusive statements can be made about taurine’s
effects in isolation from caffeine.
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