Introduction

Energy drinks (EDs) are non-alcoholic products containing caffeine, amino acids (taurine), plant stimulants (guarana), herbs (ginkgo biloba), and vitamins (niacin) [1]. EDs are used to increase energy, reduce fatigue, and improve physical and mental performance, however, they can also cause adverse effects when overused mostly due to the high level of stimulants like caffeine [2, 3]. Since Red Bull® introduced its ED to the Austrian market in 1987 and later to the USA in 1997, the market of EDs has developed at a very rapid pace [4].

Caffeine is the main active ingredient in EDs, and its excessive consumption can lead to various adverse effects [5]. According to the European Food Safety Authority, teen­agers between the age of 10 and 18 are the largest group consuming EDs. The increase in consumption and the risk of side effects influenced the World Health Organization guidelines, in which European Union countries were prompted to introduce regulations prohibiting the sale of EDs to children [6]. The overall mechanisms of ED’s side effects are not well understood, with some publications pointing at the negative impact of the individual ingredients of EDs on the cardiovascular system [7]. The main aim of this article is to present the latest information on ED consumption habits among young adults, and the possible side effects. The summary of papers used in the review was collected in Table 1.

The consumption of energy drinks among young people

The popularity of non-alcoholic beverages is increasing at a very fast pace. The recent data showing the growing number of reports of adverse effects following ED consumption can be seen as a cause for some concern, and some governments are starting to take actions aimed at reducing the consumption of energy drinks [20].

A survey conducted among students of 4th and 5th year of faculty of medicine in the Medical University of Lodz, Poland showed, that 59% of women and 86% of men (p = 0.003) declared consumption of EDs, citing the sup­port of mental health as one of the main reasons for consumption [8]. Following ED consumption 31% of students reported heart palpitations, which was the most common adverse effect caused by the consumption of EDs. About 20% of the respondents reported trembling hands/tremor and significant stimulation, and 9% of students noticed headaches. In a Canadian survey among adolescents and young adults (2055 respondents ages 12–24), 74% of respondents admitted to having ever consumed energy drinks, of which 55.4% reported that they had experienced at least 1 adverse event, including rapid heartbeat (24.7%), sleep problems (24.1%), and headache (18.3%) [9]. The prevalence of adverse effects was greater in coffee consumers than ED consumers. Another study included 68 volunteers at an average age of 25 years, who consumed 3 ED servings of 250 mL at an interval of 1 hour (total 240 mg of caffeine). Consumption of EDs caused an increase in diastolic blood pressure (BP), blood glucose levels, and increased discomfort in healthy young adults (such as headache, light chest pain, stomachache, excitation, anxiety), which was more prevalent after the second and third ED [10].

The adverse effects of consumption of energy drinks

Heart rate, blood pressure, calcium and magnesium level

Studies show that consumption of EDs can have an impact on heart rate (HR), BP, and calcium and magnesium levels [7, 11]. In the heart and smooth muscles, calcium acts as an intracellular messenger, which is involved in the activation of cardiac myocytes and muscles contraction [21]. In turn, magnesium is mainly involved in adenosine triphosphate (ATP) metabolism, myocardial and smooth muscle contraction, and relaxation through calcium reuptake [22]. In a study conducted by Kozik et al. [11], the authors showed that ED consumption (960 mL) significantly increases the baseline systolic BP by approximately 20 mm Hg (from 132 ± 7.83 to 151 ± 11.21 mm Hg, p = 0.001) [22]. Additionally, the magnesium level (change from 2.04, ± 0.09 to 2.13, ± 0.15 mEq/L, p = 0.05) and calcium level (change from 9.31, ± 0.28 to 9.52, ± 0.22 mg/dL, p = 0.018) were significantly increased compared to baseline. Similarly, Basrai et al. [12] demonstrated that 1-hour post-consumption the EDs caused an increase in systolic BP in a group of young adults (mean age 22 years), which was also observed after consumption of caffeine without taurine or glucuronolactone. The impact of caffeine consumption is mainly based on the antagonism against the adenosine receptors A1 and A2. Activation of adenosine receptors causes sleepiness and fatigue by inhibiting glutamine and dopamine secretion. Moreover, caffeine increases the secretion of norepinephrine and epinephrine by inhibiting phosphodiesterase enzymes [23]. Epinephrine and norepinephrine are synthetic amines that stimulate alpha and beta-adrenergic receptors. Their action is primarily based on peripheral vasoconstriction and increase of heart rate caused by their binding to G protein-coupled receptors on the cellular membrane [24]. The change in calcium level observed after ED consumption may be caused by the activity of taurine, which is one of the main ingredients of energy drinks. Taurine has a stimulating effect on sarcoplasmic reticular Ca2+ pump and may increase the exchange activity of Na+/Ca2+. These activities respond to the translocation of calcium from the intracellular to the extracellular space, which causes an increase in calcium level in blood [25]. The pharmacological rationale for the increase in magnesium level after consumption of EDs has not been described yet. High levels of calcium and magnesium are associated with disorders of vascular homeostasis. Magnesium acts by rendering the calcium channels available at sites critical for contraction, which allows for calcium to enter vascular cells resulting in vasoconstriction, which can further manifest as hypertension [26]. Additionally, low levels of magnesium, as well as elevated calcium to magnesium ratio, have been shown as an independent risk factor for death in patients with coronary artery disease [27]. These results emphasize the risks associated with the potential taurine-induced Ca2+ imbalance.

Shaking, dizziness and sleep disorders

Published studies indicate that the consumption of beverages containing up to 200 mg of caffeine does not cause significant adverse effects on health. However, an increase in the caffeine dose above 200 mg usually leads to shaking, dizziness, heart palpitations, and sleep disorders [8, 13, 23]. Caffeine increases the level of aminobutyric acid (GABA) A receptors and sensitivity which is most likely involved in the onset of shaking and dizziness [28]. Caffeine also stimulates the secretion of adrenaline and noradrenaline causing increased activity of the sympathetic nervous system, which is responsible for attention and arousal, thus possible sleep disorders following caffeine consumption [23]. Steinke et al. [13] showed that daily consumption of EDs (200 mg of caffeine) for 6 days caused adverse effects such as shakiness, gastrointestinal symptoms, increased urination, sleep disorders, and more forceful heartbeats in 47% of the subjects.

Torsade de pointes

Consumption of EDs can impact the cardiovascular system which can be observed in the results of the electrocardiography (ECG), where the different section of graphical heart electric activity presentation is analysed. Consumption of EDs can result in QT section elongation in ECG, which can be caused by disorders of ion channels of heart cells. It leads to ventricular abnormalities of the myocardium, specifically causing torsade de pointes (so-called ‘ballet of the heart’) [29]. Basrai et al. [12] showed that single-use of 320 mg of caffeine, 4000 mg of taurine, and 310 mg of glucuronolactone consumed in energy drinks causes the extension of the QT section from 3 to 8 ms in young adults. An increase in the interval between Q- and T-peaks is considered an indicator of substances capable of inducing arrhythmias. This effect was visible 1 hour after the consumption of EDs. So far, the mechanism of Torsade de Pointes induction following the consumption of EDs has not been discovered due to the complex interactions that occur between the various ingredients [12].

Myocardial infarction

Recently, some case reports pointed towards the existence of a relationship between the consumption of energy drinks and the occurrence of myocardial infarction in young adults [30–32]. In 2018, a 25-year-old patient was admitted to the hospital emergency department with symptoms of chest pain accompanied by nausea, vomiting, and shortness of breath [14]. The severe pain appeared suddenly and radiated to the right arm. The patient has been consuming 7–9 cans of EDs containing caffeine daily for the last week, which equals approximately 1400–1800 mg of caffeine per day. After sublingual application of nitroglycerin and intravenous administration of morphine, the patient’s condition markedly improved. ECG examination showed sinus rhythm with ST-segment depression in precordial leads V2–V6, which most likely demonstrates an anterolateral wall myocardial infarction. Additionally, laboratory results showed elevated levels of a marker of myocardial necrosis — troponin I — 32.22 μg/mL (norm < 0.07 μg/mL). A similar case concerned a 19-year-old patient, who was admitted to the hospital emergency department due to a sudden chest pain radiating to his right arm [15]. The pain subsided after sublingual application of nitroglycerin and intravenous administration of diamorphine. The patient disclosed consuming 2–3 cans of Red Bull per day in the week preceding hospital admission. ECG examination revealed 2 mm ST-segment elevation in leads I, II, aVL and V4 to V6, and 2 mm ST-segment depression in leads V1 and V2. Similarly to the previous case, laboratory tests showed an elevated level of troponin I — 34.67 μg/mL The studies showed posterolateral myocardial infarction likely caused by ED consumption. Another case described a 32-year-old male patient who was admitted to the hospital emergency department with retrosternal chest pain and emesis [16]. These symptoms occurred 5 hours before admission to the emergency department, after drinking 5 bottles of EDs, however, the authors did not specify the volume of consumed drinks. The ECG examination showed ST-segment elevation in V2–V6 leads. An emergent coronary angiogram was performed, which showed thrombi occluding 90% of the diameter of the left main coronary artery and proximal left anterior descending artery. Balloon angioplasty was performed in this case to ensure flow through the occluded vessels. Solomin et al. [17] presented a case report of another individual, a 26-year-old male who developed a myocardial infarction after ED consumption. This patient was admitted to the hospital emergency department following consumption of 4 litres of EDs daily. The patient reported pain located in the chest, the left arm, and the jaw. ECG showed significant ST-elevation in the inferior leads. Coronary angiography was performed and showed 100% occlusion of the left circumflex artery which prompted physicians to perform balloon angioplasty and insert a drug-eluting stent.

The risk of myocardial infarction was associated with the consumption of EDs, which is responsible for increasing platelet aggregation and generating endothelial dysfunction [33, 34]. Glucose, which is one of the main components of EDs causes endothelial cell dysfunction which is associated with the possibility of coronary atherosclerosis [35]. The mechanism of endothelial cell injury includes initiation of apoptosis in endothelial cells, increasing the activity of the proapoptotic protein Bax and causing activation of caspase-3 proteins by phosphorylation of the p38-MAPK pathway [36]. The cases of cardiologic side effects following the ED consumption were observed in patients as young as 19-years-old, which indicates a high risk of ED overuse among young adults, resulting in serious consequences, including myocardial infarction.

Atrial fibrillation

Atrial fibrillation (AF) is a heart arrhythmia caused by a structural remodelling of the atria and ventricles due to previous heart diseases, and the following change of the electrical discharges in the atria. AF causes irregular atrial contractions and ineffective blood flow to the ventricles, which can lead to clot formation and stroke [37]. Mattioli et al. [18] showed an association between consumption of EDs and the possibility of AF induction. After consuming a large amount (600–700 mL) of EDs, 3 patients (mean age 24 years) developed AF with high ventricular activity (ventricular rate 135–170 beats per minute). After electrical cardioversion, ECG and echocardiogram were normalized in all patients [18]. Heart arrhythmia, like AF, is often caused by electrolyte imbalances. High doses of caffeine also reduce the cellular potassium level, which can generate arrhythmia due to the stimulation of the Na/K pump. The increased activity of the Na/K pump causes hypokalemia, increasing the resting potential of myocardial cells which affects the risk of AF [38].

Conclusions

Measures restricting the sale of EDs could be needed due to the increasing number of studies reporting their negative effects on the human body. Studies show that ED consumption can cause a significant increase in BP, heart rate, prolonged QT, and cause electrolyte imbalances [11, 12, 19]. Greater attention should also be paid to the potential risk of myocardial infarction following excessive ED consumption [14]. Recent reports on EDs present the real possibility of their influence on platelet function and coagulation pathways [39, 40]. Studies describing the adverse effects of ED consumption are usually based on small study groups, therefore future efforts should focus on performing research on larger cohorts with emphasis on observed side effects for more comprehensive evaluation.

The expansion of ED consumption is taking place at a rapid pace. One of the main solutions to the potential problems it may cause is rational and responsible consumption. Consumption of EDs can help with concentration, physical and mental performance, and reduce fatigue, but they also should be consumed in moderation due to several adverse effects. Due to the increasing consumption of EDs, it is important to pay increased attention to the adverse effects of the following consumption and to investigate their mechanisms. Therefore, asking about frequency and volume of consumed EDs as well as their ingredients for complete medical history should be considered more often, especially among younger patients, and patients presenting cardiac symptoms.

Author contributions

The roles of authors: Hałasiński Przemysław: was responsible for the conception and design of the study, literature search, writing of the first draft and subsequent drafts. Musielak Marika: was responsible for reviewing the paper for completeness, critical revisions of the manuscript. Piotrowski Igor: was responsible for reviewing the paper for completeness, critical revisions of the manuscript, and approval of the final version submitted for publication.

Conflict interest

The authors declare that there are no conflicts of interest.

Funding

The authors declare that there are no funding.