Energy drinks have a high caffeine content which is normally combined with large amounts of vitamins, minerals, taurine, amino acids, and different mixtures of phytochemicals.
Energy drinks first made their appearance in Europe and Asia in 1960. Energy drinks first appeared in Austria in 1987 with a well-known brand and erupted across the globe over the following years. Their consumption has increased exponentially as they have gained in popularity and it has now become a multibillion-dollar industry [1].
It is necessary to differentiate between energy drinks and traditional beverages (coffee, tea, isotonic, hypotonic and hypertonic sports drinks, and soft drinks such as cola). Energy drinks have a high caffeine content which is normally combined with large amounts of vitamins, minerals, taurine, amino acids, and different mixtures of phytochemicals [2].
This type of drink has gained particular prominence, as evidenced by its consumption by various demographic groups, with and without risks of disease, such as youths, workers, students, professional athletes, amateur athletes, and nightlife revelers [3]. No countries restrict or place age limits on the consumption and sale of energy drinks, so they are readily accessible to all populations and ages.
Regarding physical exercise, energy drinks form part of training prioritization in terms of the physical qualities to condition, nutritional practices, pharmacological approach or psychological techniques that can improve training adaptations and/or the output of the exercise [4]. This includes aids that may benefit individuals when exercising, increase the efficiency of the exercise and/or improve subsequent recovery [4][5].
The use of dietary supplements is widespread throughout the general population, but it takes on particular importance for those who practice sports and their consumption by athletes corresponds to a significant proportion of their sales [4][6][7][8]. Dietary supplements can play an important role in helping athletes achieve an ideal intake of calories and nutrients. However, they should never be considered as a substitute for a healthy diet [4].
Energy drinks have emerged as a key dietary supplement to enhance athletic performance, particularly in the acute consumption, with the effects of caffeine and taurine being the most studied in several different sports [9][10][11]. The association between performance and the consumption of energy drinks has been demonstrated in American football and soccer [12][13][14], athletics [15][16][17], volleyball [18], and handball [19], amongst others. Although there is comprehensive evidence of the positive association between the consumption of these drinks and improved sporting performance, there are risks in terms of the potential for cardiovascular problems due to hypertension, altered sleep patterns in adolescents, aggravation of mental illnesses, physiological dependence and an increased possibility of subsequent addiction [20][21], while their potential for toxicity can result in tachycardia, arrhythmia, vomiting, convulsions and even death [22]. The adverse effects of energy drink intake may occur in healthy people, but some people may be particularly prone to complications. High-risk groups include young, caffeine-deficient or caffeine-sensitive pregnant women, competitive athletes, and people with underlying cardiovascular disease [23]. Moreover, the effects of chronic high-dose caffeine and taurine intake in children, adolescents and athletes are not yet known [22].
Possibly one of the most interesting areas for research regarding the consumption of energy drinks associated with athletic performance and the observed cardiovascular risks would be to study the genetic markers that indicate a greater predisposition to improve performance by consuming energy drinks [24] and a protective effect against the damage they can cause to the cardiovascular system. The field of nutrigenomics is expanding our understanding of sports performance [25], but it is still a long way from obtaining evidence-based knowledge. In the area of caffeine, recent evidence related to cytochrome P450 1A2 (CYP1A2) -163C>A polymorphism has helped optimize the caffeine dose an athlete needs to improve their performance [26][27][28] in endurance sports [29], as well as in team sports and explosive efforts [19][28][30][31].
Several studies have shown significant relationships between the consumption of energy drinks, sports performance and increased prevalence of cardiovascular risk factors. However, the results reported to date remain inconsistent, so a full general description of the studies in this field is necessary. For a more detailed analysis of the matter, we have classified recent studies according to the differences in the associations between the energy drinks and: (i) Athletic performance; (ii) cardiovascular risk factors while practicing sports; and (iii) genetic associations and future prospects between the consumption of energy drinks and performance.
Coffee and caffeine influence the cardiovascular system through their positive inotropic and chronotropic effects, affecting the central nervous system by stimulating locomotor activity and anxiogenic effects. This underlines the need to examine whether these effects may be harmful to health, particularly in the world of sport [32].
Reissig et al. [33] have described several effects linked to excessive caffeine consumption. Over a lifetime, people should only consume large amounts of caffeine for short periods, but this sort of consumption is more common on a regular basis. Furthermore, some people use caffeine to improve their concentration and memory or enhance their physical performance and, in some cases, could develop a dependence syndrome. Caffeine use transforms into “abuse” when individuals develop an uncontrolled need to consume caffeine, even if it is harmful to their health; it transforms into “dependence” when mechanisms of tolerance and abstinence develop, and certain chronic usage habits make caffeine even more damaging. Along with caffeine dependence, subjects who consume extremely high doses continuously for years, ignoring all safety concerns by combining two or more sources of caffeine, for example, coffee and energy drinks, without any evidence that such combinations provide any desirable benefits [32].
Given the significant number of incidents reported among energy drink consumers, it seems pertinent to summarize the available data and establish causal links between the use of these products and the development of health complications. Occasional to moderate consumption of these drinks seems to pose little risk to healthy adults. However, excessive consumption related to their combination with drugs in amounts that far exceed the manufacturers’ recommended intakes could induce negative consequences for human health, especially among subjects with cardiovascular disorders [34].
The risk factors may increase the rate of adverse events, particularly cardiovascular events in individuals who consume energy drinks, due to underlying conditions [35], and they may suffer a caffeine overdose, as has been reported in the literature [22][34][36][37][38]. A lethal dose of caffeine has been noted as 5 g, which is equivalent to approximately 42 cups of coffee with 120 mg caffeine/cup [37]. Sepkowitz et al. [39] suggested that the acute intake of 3 g of caffeine can provoke significant side effects, which may even be fatal, with arrhythmia being the most common factor producing death by this lethal dose. A review by Nawrot et al. [40] stated that a healthy adult can consume up to 400 mg of caffeine/day (equivalent to 6 mg/kg in individuals weighing less than 65 kg) without being associated with any adverse effects.
The combined use of caffeine and ephedra has been reported also as a risk factor for cardiovascular problems [41]. There is evidence to suggest that the short-term use of ephedra, with caffeine, promotes short-term weight loss. One example is the meta-analysis by Shekelle et al. [42] in which subjects who took caffeine and ephedrine lost around 0.9 kg/month more over a short period than the placebo group (p < 0.01), no regarding long-term weight loss to support the use of ephedra for athletic performance (p > 0.05). Ephedra is known to be ergogenic during anaerobic exercises, such as bench presses (p < 0.05), especially when taken with caffeine; however, a point to consider is that systolic blood pressure increased significantly before both tests in subjects treated with ephedrine compared to the other tests [43]. A clinical trial by Haller et al. [44] carried out in 16 healthy subjects showed an increment in the stimulating and metabolic effects of combined ephedrine (25 mg) and caffeine (200 mg) as they increased systolic blood pressure (maximum difference of 11.7 ± 9.4 mmHg compared to placebo; p = 0.0005) and heart rate (maximum difference of 5.9 ± 8.8 beats/min; p = 0.001). The study demonstrated that, individually, ephedrine and caffeine had modest effects, but in combination, they produced significant cardiovascular, metabolic, and hormonal responses at moderate doses, data which should be taken into account to avoid such risks when indicating the dose to produce the desired ergogenic effect.
This entry is adapted from the peer-reviewed paper 10.3390/nu13030715