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Examining the effects of energy drink composition on cardiovascular activity, EEG and reaction time

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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