In recent years, the consumption of energy drinks by young adults and athletes has risen significantly, but concerns have been raised about the potential health risks associated with excessive consumption. These concerns include cardiovascular problems, nervous system disorders, and the potential for addiction. This review aims to examine the reported effects of acute or chronic abuse of energy drinks on human health. The analysis shows a significant prevalence of adverse effects, particularly on the cardiovascular and neurovegetative systems. In particular, the analysis identified nine cases of cardiac arrest, three of which were fatal. The aetiology of these adverse effects is attributed to the inherent neurostimulant properties of these beverages, of which caffeine is the predominant component. A comparison of documented effects in humans with experimental studies in animal models showed an overlap in results. This review highlights the need for greater rigour in the assessment of sudden cardiac death, particularly in young people, as legal substances such as energy drinks may be involved. We propose stricter limits on the consumption of these beverages than for caffeine, based on the evidence found and the data in the literature. This review also calls for the establishment of regulations governing the consumption of these products in view of their potential impact on human health.
1. Introduction
The Food and Drug Administration (FDA) defines energy drinks (EDs) as “a class of products in liquid form that typically contains caffeine, with or without other added ingredients.” They typically contain large amounts of caffeine, added sugars, other additives, and legal stimulants such as guarana, taurine, and L-carnitine. These legal stimulants can increase alertness, attention, and energy, as well as increasing blood pressure, heart rate, and breathing. These products are marketed as enhancers of mental acuity and physical performance [1,2]. Prominent examples of energy drinks include Red Bull, Monster, NOS, Rockstar, Lucozade, Eastroc Super Drink, Bang Energy, and 5 Hour Energy [3,4], as described in Table 1. Adolescents gravitate towards these beverages to swiftly boost energy levels, enhance alertness, and increase scholastic or athletic performance.
Consequences of this consumption pattern have led to a rising incidence of young individuals seeking medical attention in emergency departments due to an array of adverse health outcomes, as documented in results section. Reports underscore that energy drinks have deleterious effects on a broad spectrum of bodily organs, culminating in mild adversities such as anxiety, gastrointestinal disturbances, dehydration, nervousness, and tachycardia, along with more severe outcomes like rhabdomyolysis, acute kidney injury (AKI), ventricular fibrillation, seizures, acute mania, and stroke. Furthermore, instances linking energy drink consumption to fatalities have been documented.
The rise of the energy drink market, particularly within the younger demographic, has caused a 70% escalation in caffeine ingestion among caffeine-consuming children and adolescents from 1977 to 2009 [1]. Data sourced from the National Health and Nutrition Examination Survey spotlight an average caffeine intake of 61 mg daily for teenagers [5]. While youth caffeine consumption has receded in recent decades, the utilisation of energy drinks has concurrently surged [5].
These beverages substantially differ in both caffeine content (ranging from 50 to 505 mg per can or bottle) and caffeine concentration (ranging from 2.5 to 171 mg per 28 mL). By comparison, a 170 g cup of brewed coffee contains caffeine concentrations varying between 77 and 150 mg [3].
As shown in Table 1, energy drinks are composed of a variety of ingredients, including taurine, ginseng, sugar, guarana, etc.
Table 1
| Energy Drink | Caffeine (mg) | Sugar (g) | Other Ingredients |
|---|---|---|---|
| Red Bull | 160 | 54 | Taurine (2000 mg), gluconolactone (1200 mg), inositol N/S [not specified] and vitamins B3, B5, B6 and B12 N/S |
| Monster | 160 | 54 | Taurine (2000 mg), gluconolactone N/S, carnitine N/S, inositol and guarana N/S, ginseng (400 mg) and vitamins B2, B3, B6 and B12 (40 mg) |
| Rockstar | 160 | 62 | Taurine (2000 mg), carnitine (50 mg), inositol (50 mg) and guarana (50 mg), ginseng (50 mg), gingko biloba (300 mg), milk thistle (40 mg) and vitamins B2, B3, B5, B6 and B12 (50 mg) |
| Mountain Dew | 72 | 61 | Carbonated water, high-fructose corn syrup, concentrated orange juice, citric acid, natural flavour, sodium benzoate, caffeine, sodium citrate, gum arabic, erythorbic acid, calcium disodium, yellow 5 |
| Race | 160 | 0 | N/S |
| Sting | 290 | 50 | Taurine (148 mg), inositol (21 mg), ginseng (9.7 mg), vitamin B3 (10.2 mg) |
| Magnus Omnilife | N/S | N/S | N/S |
| Demon Energy Shot (sold in 60 mL) | 1600 (200 mg per 60 mL) | N/S | Taurine (10 g), glucuronolactone (N/S), inositol (N/S), B3 (N/S), guarana (60 mg), B5 (N/S), B6 (N/S), B12 (N/S) |
| Full Throttle | 141 | 57 | Taurine (N/S), guarana (N/S), B3 (N/S), B6 (N/S), B8 (N/S), carnitine (N/S) |
| Lucozade | 60.5 | 23 | Carbonated water (N/S), citric acid (N/S), sodium gluconate (N/S), potassium sorbate (N/S), aspartame (N/S), acesulfame K (N/S), flavourings (N/S), sunset yellow (N/S), ponceau 4R (N/S), ascorbic acid (N/S). |
In particular, taurine and gluconolactone are claimed to be the main components responsible for the effects attributed to Red Bull. Taurine, a derivative of the amino acid cysteine, is found abundantly in cardiac and skeletal muscles [7,8]. Its engagement covers various physiological functions encompassing neuromodulation, cell membrane stabilisation, and the regulation of intracellular calcium levels [9]. Acknowledged for its anti-arrhythmic attributes, taurine’s capacity for cation transport regulation contributes to its effect [10]. It is instrumental in modulating the inwardly rectifying K+ current and action potential duration in cardiac muscles [11], along with inhibiting the fast Na+ current, thereby evoking class I antiarrhythmic activity [12]. Its presence in significant concentrations within the brain underscores its pivotal role in neuroprotection and neurotransmission enhancement [13]. The prospect of taurine in tandem with caffeine bolstering concentration, reaction time, and emotional state has sparked investigation, although conclusive evidence on combinatorial cognitive effects remains elusive. Seidl et al. conducted a double-blind, placebo-controlled trial administering caffeine, taurine, and glucuronolactone to the experimental group, yielding shorter motor reaction times and higher emotional well-being scores [14]. While the study implied a positive cognitive impact, GABAergic, glycinergic, cholinergic, and adrenergic neurotransmitter system interactions were posited, acknowledging the caffeine factor [15].
Gluconolactone, an outcome of hepatic glucose metabolism, stands as a precursor for ascorbic acid synthesis. In the 1960s, Japanese researchers [16] directed attention toward its performance-amplifying attributes. A study demonstrated enhanced swimming endurance in laboratory rats following the direct intestinal injection of glucuronolactone, glucose, glycogen, and other agents, with the former group outperforming in two of three instances. The findings suggest that the equivalent human dose could range from 1 to 2 g of glucuronolactone, compared to 600 mg in a Red Bull can. Detoxifying potential may contribute to these results, as glucuronolactone supplementation may fortify the body’s natural defences against carcinogens and tumour promoters [8].
Among the additional ingredients commonly found within energy drinks, carnitine, guarana, and the vitamin B complex should be mentioned.
Carnitine, comprising several compounds, including L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine [17], emerges as a derivative of an amino acid. It occurs naturally in numerous foods, particularly animal-derived foods, and is available in dietary supplement form. Carnitine synthesis transpires endogenously within the liver, kidneys, and brain from the amino acids, lysine and methionine [18,19]. This compound plays a pivotal role in energy production, serving as an indispensable cofactor that facilitates the transport of long-chain fatty acids into mitochondria for oxidation, leading to adenosine triphosphate (ATP) energy generation [20,21].
Guarana (Paullinia cupana), a climbing plant native to the Amazon, has historically served as a stimulant and traditional medicine among Brazil’s indigenous peoples [22]. Guarana seeds notably surpass coffee beans in caffeine content, containing additional xanthine alkaloids such as theobromine and theophylline [23]. This botanical additive enhances the caffeine content and stimulatory attributes of energy drinks (EDs), with its caffeine content being unlisted on product labels due to its status as an herbal supplement [24].
Comprising eight B vitamins, the vitamin B complex includes thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine hydrochloride (B6), biotin (B7), inositol (B8), and cyanocobalamin (B12). These vitamins act as coenzymes that are integral to proper cellular function, particularly in mitochondrial activity and energy production. Hence, there is some conjecture that B vitamins might increase energy expenditure [25].
The aim of this review is to summarise all evidence on the adverse effects of energy drink consumption.
2. Materials and Methods
This systematic review follows the Preferred Reporting Items for Systematic Review (PRISMA) standards [26] (Figure 1). In the context of specific events, such as acute intoxication or preliminary reports of legal substances, we believe that case reports/studies and case series involving human subjects with medical reports can provide valuable evidence for systematic reviews. Therefore, descriptive observational study designs, including case series, individual case reports, and descriptive cross-sectional studies, were considered for inclusion in this review. We conducted a comprehensive literature search and critically appraised the collected studies. An electronic search was conducted using PubMed, Google Scholar and EBSCO search engines to identify peer-reviewed articles published between 5 January 2009 and 30 April 2023, using the search terms ‘energy drink’, ‘Red Bull’, ‘Monster’, ‘taurine’, ‘adverse effects’, ‘arrhythmia’, ‘renal failure’, ‘death’, ‘gastrointestinal’ in the title, abstract and keywords. Internet search engines such as Google were also used to find relevant information. In addition, the reference lists of all retrieved papers were reviewed and cross-referenced to identify additional relevant literature. Only English-language papers were included in this study. Data on each case were extracted, including age and sex of the case, brand of energy drink consumed (some brands were unknown), main pathologies, type of event and onset. Two or more independent reviewers screened titles and abstracts against the inclusion criteria for the review. The results of the search and study inclusion process were reported in detail in the final systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. In addition, case–control studies using animal models were included in the review to compare data from human case reports. The above search identified 458 articles, which were screened to exclude duplicates. The resulting reference lists were then screened for titles and abstracts, leaving 442 articles for further consideration. Non-English articles were excluded. The inclusion criteria were as follows: (1) original research articles and (2) case reports/series. These publications were carefully assessed, taking into account the main objectives of the review. Reviews and mini-reviews were not included in the qualitative synthesis but were used to check for missing articles. After this evaluation, 96 scientific papers remained.
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