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, , however the active ingredients of which are primarily appreciated to be caffeine and taurine .
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, . 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 . This could explain the findings of Huxtable et al. , 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 .
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.
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 . Also, if accompanied by stress, caffeine can
increase peak systolic BP to hypertensive levels . In these
studies, the stress was caused by giving the subjects a task to
complete , 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 . The mechanism of
these actions has not been fully elucidated but is thought to be due to
its anti-oxidant, cytoprotective effects .
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.
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 . 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.
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