Although the consumption of energy drinks is somewhat declining [
In terms of physiological effects of Red Bull©, most of the documented changes have focused on the subjects’ blood pressure (BP) and heart rate (HR) at rest [
Even though Red Bull© is promoted as energy drink that improves mental alertness and performance, the number of studies that researched this topic is limited. Alford et al. found that Red Bull© improved reaction times, alertness, and concentration and that improved performance on an immediate recall memory test in young healthy students [
Since activation of sympathoadrenergic system is crucial in cardiovascular and psychomotoric reactions and Red Bull© has ingredients that could modulate levels of adrenergic hormones, the aim of our study was to determine the involvement of adrenergic system in effects contributed to Red Bull© consumption on (1) HR, BP, blood glucose, and plasma catecholamines levels at rest, (2) cardiac, and respiratory changes before, during, and after moderate exercise, (3) reaction time to audio stimuli, (4) cognitive functions, and also (5) response to mental stress (distracting three digit numbers) test and emotions in young healthy individuals.
Thirty-eight young healthy medical students were recruited for the study by advertisement at the Faculty of Medicine Josip Juraj Strossmayer, University of Osijek. All volunteers were self-described as healthy, with no history of cardiovascular, urinary, digestive, or metabolic diseases. All subjects were familiar with Red Bull© and most of them had previously consumed this energy drink. Written informed consent was obtained from each subject. The study protocol and procedures conformed to the standards set by the latest revision of the
All subjects were instructed not to consume alcohol or energy drinks 7 days prior testing. They all were fasting 12 h prior to the onset of the experiment. Subject height and weight were measured to determine body mass index (BMI), as well as the extent of hips and waist to determine waist-to-hip ratio (WHR). BP and HR were measured at the beginning of the experiment after 15 minutes rest in seated position. Semiautomatic oscillometric monitor (OMRON) was used. Final values of BP and HR were mean of three repeated measurements. Intravenous cannula was inserted into a vein and a venous blood sample was taken after 30-min resting in supine position. A separate group of 9 participants stay resting in supine position during whole study visit and blood samples for plasma catecholamine levels were taken after 30 minutes resting in supine position (before Red Bull© consumption) and 15, 30, 45, and 60 minutes after 500 mL of Red Bull© consumption. This was necessary due to great variability in catecholamine levels when person in moving and results of the measurements would be inconclusive for the observed effects. Prior to Red Bull© consumption, other 29 participant were assigned to 4 different study protocols (described below) by randomized order. After control protocol subjects were instructed to drink 500 mL of Red Bull© and after 30 minutes of resting in supine position, all tests, including BP, HR, blood tests, and each of 4 study protocols were repeated by randomized order.
The Harvard Step Test (HST) was used to detect cardiac and respiratory changes during moderate exercise. The HST is performed in a manner that the subject steps up and down into the default beat for three minutes on the 45 centimeters high step bench. Male participants had stepped on the bench 24 times in one minute (24/per min), while female participants had stepped on the bench 22 times in one minute (22/per min). For determining the rate, metronome was used and was set at 96 beats per minute for male subjects and 88 beats per minute for female subjects. Each tick marked a movement with subject’s leg. At the START signal participant stepped up, first with one foot on the bench, and then another, and after stretching legs and straightening back immediately stepped down, gliding with leg which first stepped up. Stepping up and down always started with the same leg (with maximum two changes during the test). In one hand subject held air flow transducer and temperature sensor was attached to his other hand. The physiological functions of the subject were measured during seven minutes, first minute at rest, next three minutes during stepping up and down, and last three minutes at rest after exercise.
Three parameters were measured during this study protocol: HR, air flow, and skin temperature (ST). These parameters were assessed with three electrodes attached to subject’s chest, air flow transducer into which subject breathed with clamp on his nose and skin temperature sensor mounted on his finger which were all connected to BIOPAC device (BIOPAC Systems Inc., Goleta, CA, USA). For data processing BIOPAC software was used (BIOPAC Systems Inc., Goleta, CA, USA). All measurements were performed by a single trained operator.
Reaction time (RT) was measured by BIOPAC device and software (BIOPAC Systems Inc., Goleta, CA, USA). Measurement was performed in quiet room. Subject was sitting eyes closed with headphones and with push-button device in his hand which he pressed on sound signal. The first part of the test consisted of series of ten beeps that occurred in randomized time intervals, and second part in which beeps occurred in fixed time intervals. Both tests lasted for one minute, with one minute pause between tests.
All cognitive tasks were assessed by randomized order in quiet room by a single trained operator. For cognitive function assessment following tests were used.
The Beck Anxiety Inventory (BAI), created by Dr. Aaron T. Beck and other colleagues, is a 21-question multiple-choice self-report inventory that is used for measuring the severity of an individual’s anxiety. The BAI consists of twenty-one questions about how the subject has been feeling in the last week, expressed as common symptoms of anxiety (such as numbness, hot and cold sweats, or feelings of dread). Each question has the same set of four possible answer choices, which are arranged in columns and are answered by marking the appropriate one with a cross. These are (1) not at all, (2) mildly: it did not bother me much, (3) moderately: it was very unpleasant, but I could stand it, (4) severely: I could barely stand it. In our study the version of this test with 14-question multiple-choice self-report inventory was used [
Blood samples were analyzed for blood glucose levels and plasma catecholamine levels at the Department of Clinical Laboratory Diagnostics, University Hospital Center Osijek. Adrenaline and noradrenalin levels were evaluated by using commercially available reagent kit (Catecholamines in plasma, Chromsystems, Germany) which allows the routine analysis of adrenaline and noradrenalin in plasma using an isocratic high-performance liquid chromatography (HPLC) system (Shimadzu, Japan) and an electrochemical detector (ECD, Chromsystems, Germany).
All results are presented as mean ± SD. The normality of data distribution was assessed by Kolmogorov-Smirnov Normality test. Clinical characteristic between two measurements (before and after Red Bull© consumption) were compared by paired
Thirty-eight young healthy college students with a mean age of 23 ± 2 years completed the study (15 female and 23 male participants). BMI of 23.95 ± 3.03 kg/m2 and WHR of 0.79 ± 0.05 were measured. Mean of three BP measurements confirmed normotension before Red Bull© consumption among participants. Table
Arterial blood pressure and heart rate of study population.
Variable | Before Red Bull |
After Red Bull |
|
---|---|---|---|
SBP | 113 ± 12 | 115 ± 12 | 0.151 |
DBP | 68 ± 10 | 70 ± 8* |
|
MAP | 83 ± 10 | 85 ± 9* |
|
HR | 71 ± 10 | 76 ± 11* |
|
Results are expressed as mean ± SD.
SBP: systolic blood pressure, DBP: diastolic blood pressure.
MAP: mean arterial pressure, HR: heart rate.
*
Figure
Influence of Red Bull© on plasma adrenaline and noradrenalin levels.
Measurement of HR, respiration rate (RR), and respiratory flow rate (RFR) during 1-minute rest before the beginning of Harvard Step Tests (HST) has shown significant changes after Red Bull© consumption. The first-minute HR during rest before the beginning of HST was significantly increased after Red Bull© intake compared to control condition before Red Bull© intake (HR/min 89 ± 10, 103 ± 14, resp.;
Change of heart rate (HR) during 1-minute rest, 3 minute of Harvard Step Test, and 3-minute rest after exercise before and after Red Bull© consumption.
Change of respiration rate (RR) during 1 minute rest, 3 minute of Harvard Step Test and 3 minute rest after exercise before and after Red Bull© consumption.
Change of respiratory flow rate (RFR) during 1-minute rest, 3-minute of Harvard Step Test, and 3-minute rest after exercise before and after Red Bull© consumption.
Same parameters were measured during 3 minutes of HST before and 30 minutes after Red Bull© intake. As expected, HR, RR, and RFR were increasing with the exercise duration before and after Red Bull© consumption. ST did not change during 3 minutes of HST before and after Red Bull© intake. HR was significantly higher (
As expected, HR, RR, and RFR were decreasing during 3 minutes rest after control HST and HST that followed Red Bull© intake. Still, HR (Figure
Reaction time (RT) was measured before and after Red Bull© consumption. In both measurements, subjects reacted faster when sound signals appeared in randomized time intervals compared to the RT when sound signals appeared in fixed time intervals (RT sec before Red Bull© 0.26 ± 0.04, 0.29 ± 0.04,
Table
Scores achieved on tested cognitive tasks.
Cognitive function | Task | Before Red Bull |
After Red Bull |
|
---|---|---|---|---|
Immediate memory | AVLT- (1-) first trial | 8,17 ± 1,77 | 7,79 ± 2,04 | 0,426 |
ADST-forward | 8,03 ± 0,82 | 8,48 ± 0,87* |
|
|
Delayed recall | AVLT-delayed recall | 12,58 ± 2,18 | 13,00 ± 1,93 | 0,231 |
Working memory | ADST-backwards | 6,45 ± 0,83 | 6,86 ± 1,03* |
|
Delayed verbal memory | AVLT-late recall | 12,55 ± 1,97 | 12,03 ± 3,15 | 0,459 |
Verbal fluency | Semantic task | 23,28 ± 3,89 | 26,10 ± 4,94* |
|
Ideational task | 15,07 ± 4,00 | 18,66 ± 4,43* |
|
|
Phonemic task | 30,70 ± 7,31 | 41,76 ± 9,71* |
|
|
Attention |
d2 test TN-E | 486,83 ± 69,19 | 592,45 ± 60,31* |
|
d2 test MC | 267,90 ± 27,90 | 283,21 ± 21,89* |
|
Results are expressed as mean ± SD.
AVLT: auditory verbal learning test; ADST: auditory digit span task; TN-E: quantitative measure defined by total number of processed data minus number of total errors; MC: mean concentration.
*
Participants’ response to the mental stress test (MST) was significantly better after Red Bull© intake compared to the control (MST points control 146.56 ± 50.73 versus points after Red Bull© 189.31 ± 48.03,
The salient finding of the present study is that Red Bull© consumption (1) increased activity of the sympathetic nervous system (by increased plasma adrenaline and noradrenalin levels); (2) subsequently affected cardiovascular and respiratory system during rest and exercise; and (3) improved cognitive functions, as well as the performance in mental stress test and reaction time, while (4) Red Bull© consumption did not have significant effect on subject’s emotional status, precisely aggression and anxiety. Red Bull© consumption significantly increased MAP and HR as well as RR and RFR, at rest and during exercise in young healthy population, all of which are under adrenergic control; it had beneficial effect on cognitive functions (immediate memory, attention, and verbal fluency), improved performance in MST, and improved RT. However, consumption of Red Bull© has not altered subject’s emotional status, including aggression and anxiety. 500 mL Red Bull© consumption significantly increased blood glucose levels, as well as plasma adrenaline and noradrenalin levels. To our knowledge this is the first study which demonstrated that Red Bull© consumption leads to adrenergic system activation with subsequent changes in both cardiovascular and psychomotoric reactions in young individuals.
We have found significantly increased DBP and MAP while SBP increased but without significance after Red Bull© consumption. HR was significantly increased 30 minutes after Red Bull© intake. These results are consistent with Steinke et al. who observed influence of 500 mL energy drink through 7 days and reported elevated DBP within 2 hours of energy drink consumption as well as elevated SBP and HR at day 1 of energy drink consumption [
Blood glucose level significantly rose 30 minutes after Red Bull© consumption. This significant increment can be attributed to intake of almost 56 g of sugars (glucose 10,5 g and saccharose 43 g) in 500 mL of Red Bull©. However, it has been shown that activation of adrenergic system via physical or emotional stress increases blood glucose levels (max glucose levels reached 30 minutes after stress stimulation) [
To our knowledge, this is the first study that measured the impact of Red Bull© consumption on respiratory function at rest and during exercise. We found significantly increased RR as well as RFR at rest, during exercise and at rest after exercise. This effect of Red Bull© can also be explained by activation of sympathetic nervous system, which leads to increased RT and greater alveolar oxygen exchange due to bronchioles dilation.
However, although potential link between energy drink consumption and increased sympathetic activity is accentuated in numerous studies, there is a lack of actual measurement of plasma catecholamine levels in response to Red Bull© to support these speculations. That is the reason why in the present study we have measured plasma concentrations of adrenaline and noradrenalin in five different time points (before Red Bull© consumption and 15, 30, 45 and 60 minutes after Red Bull© consumption) and demonstrated that both adrenaline and noradrenalin plasma levels were increased after Red Bull© intake through the time in which different study protocols were randomly performed compared to values before Red Bull© intake (Figure
Our finding that Red Bull© intake improved RT is consistent with Alford et al. who reported that Red Bull© improved reaction times, alertness and concentration, mental acuity skills that might be considered important to college students [
As Red Bull© is advertised and sold as energy drink that beside physical, improves and mental performance, it is really important to find its real effect on cognitive functions. Results of our study have shown significant improvement in working memory, verbal fluency and attention tests performance after Red Bull© consumption. Immediate memory was significantly improved after consuming Red Bull©, when measured as number of correctly repeated numbers in forward order. In already mentioned study, Alford et al. found that Red Bull© improved cognitive performance [
Limitations of the study: the study was organized as before and after the treatment study, where subjects were self-controls. Due to particular taste of Red Bull©, it was not possible to blind subjects or examiners on the beverage taken. Because Red Bull© intake obviously has important effect on glucose metabolism and blood glucose level, a glucose tolerance test would be interesting to perform, to exclude possibility that glucose is high due to intolerance and not due to high glucose content in the Red Bull© to. However, as stated in Methods section, participants in this study were healthy young people with normal fasting glucose levels and no positive history of diabetes or prediabetes or glucose intolerance.
In conclusion, our study has shown consistent positive effects of Red Bull© energy drink on cognitive functions (immediate memory, attention, and verbal fluency), improved performance in mental stress test and improved reaction time. These positive effects are consistent with the assertions of Red Bull© manufacturers and one of the main reasons why are precisely young people and college students the main consumers of Red Bull©. However, results of this study have shown that 500 mL of Red Bull© may have adverse effect on cardiovascular and respiratory system, leading to increased MAP and HR as well as RR and RFR, at rest and during exercise. Precisely because the target market for Red Bull© is people between 15 and 30 years of age, that is, typically healthy, involved in activities, and includes a higher proportion of sports enthusiasts and high-risk takers, these effects should not be neglected. Other main problems involved in Red Bull© consumption are that its numerous ingredients and its effect is difficult to assign to one specific ingredient. This is first study that has actually shown increased activity of the sympathetic nervous system (increased plasma adrenaline and noradrenalin levels) after Red Bull© consumption which may have an important role in its observed effects on cardiovascular and respiratory system during rest and exercise, on cognitive functions as well as on performance in mental stress test and reaction time and thus elucidated important mechanism of its’ action.
The study protocol and procedures conformed to the standards set by the latest revision of the
Written informed consent was obtained from each subject.
The authors have no conflict of interests to declare.
Ana Cavka and Marko Stupin equally contributed to this paper.
Authors thank Professor Gordana Bujisic, M.D., Ph.D., for providing tests for cognitive function assessment, aggression questionnaire, and Beck Anxiety Scale. This study was partially supported by a Grant of the Ministry of Science, Education, and Sports of the Republic of Croatia, Effects of oxygen on vascular function in health and disease, no. 219-2160133-2034.