Beverages containing sugar for energy and caffeine for mental stimulation have been around for a long time. Of course, caffeinated nondiet sodas fit this description, with some varieties containing as much added caffeine as a typical cup of coffee. But the term energy drink typically refers to “beverages that contain high levels of caffeine plus specialty ingredients not commonly found in sodas and juices” (Harris and Munsell, 2015, p. 248). Current interest in energy drinks and their smaller cousins, energy shots, can be traced to the introduction of Red Bull in 1987. Sales of these beverages began to rise slowly and then more rapidly over time, coinciding with the creation of many competitor brands such as Monster Energy and Rockstar. Global sales of energy drinks rose from $3.8 billion in 1999 to $27.5 billion in 2013, an increase of roughly 620% (Ferdman, 2014).
Energy drinks are claimed to boost energy and alertness, alleviate fatigue, assist recovery from lack of sleep, and improve athletic endurance and performance (Reissig et al., 2009). These drinks contain caffeine in varying amounts (listed either as caffeine itself or as guarana, a caffeine-containing plant extract), sugar (except for “diet” drinks), and often other ingredients such as the amino acid taurine, L-theanine (a naturally occurring glutamate analog), ginseng, sodium, and vitamins. Caffeine content of energy drinks varies widely, from 80 mg (similar to a standard cup of brewed coffee) in Red Bull to 400 mg (equivalent to five cups of coffee) in a single 5 ml serving of Fixx energy shot. A survey of college students at a state university in the central Atlantic region of the United States found that energy drinks were most often consumed in the following situations: insufficient sleep, a general desire for increased energy, needing to study or to work on a major project, driving a car for a long period, partying (in which case the energy drink was consumed with alcohol), and recovering from a hangover (Malinauskas et al., 2007). The majority of energy drink consumers surveyed used these beverages on 1 to 4 days per month, but approximately 5% to 10% used energy drinks on more than 10 days per month.
Do energy drinks work as advertised? Controlled studies either with a commercially available drink such as Red Bull or with prepared mixtures that duplicate typical energy drink constituents do indicate that these beverages can improve performance on measures of subjective alertness, concentration, memory, reaction time, and physical endurance (Alford et al., 2001; Scholey and Kennedy, 2004; Smit et al., 2004). Although some investigators have argued that the positive effects of energy drinks are simply due to reversal of caffeine deprivation (Smit et al., 2004), research described elsewhere in this chapter on the performance-enhancing effects of pure caffeine administration suggests that the caffeine content of energy drinks may be capable of significantly improving performance beyond that of mere deprivation reversal. In some instances, multiple constituents of energy drinks may work together to promote the desired effects. This has been demonstrated experimentally for the enhancement of cognitive function by caffeine plus glucose or caffeine plus L-theanine (Childs, 2014), and for the improvement of motor skills in athletes by caffeine and carbohydrates such as glucose (Baker et al., 2014).
Despite these positive findings, a few concerns have been raised about the regular use of energy drinks. The first concern is centered around the ability of heavy caffeine consumption to cause sleep disturbance (Wesensten, 2014). This can occur at any age but is particularly problematic in children and adolescents. Second, consumers should be aware that overconsumption of energy drinks can pose serious health risks. Between 2005 and 2011, the number of reported energy drink-related visits to U.S. hospital emergency departments rose from 1494 to 20,783 (Substance Abuse and Mental Health Services Administration, 2013). Some of these cases involved consumption of an energy drink in combination with other substances, including alcohol, CNS stimulants, or marijuana. Among the reported effects of energy drink overdosing are agitation, tremors, seizures, damage to the liver and kidneys, gastrointestinal distress, respiratory problems, and cardiovascular abnormalities such as cardiac arrhythmia, tachycardia, and even heart failure (Gunja and Brown, 2012; Seifert et al., 2011). A small number of fatalities have also been reported, typically as the result of cardiac arrest (e.g., Cannon et al., 2001; Rottlaender et al., 2012).
Yet another concern has been raised around the combination of alcohol with energy drinks. A few energy drinks already contain alcohol, whereas in other cases, people consume energy drinks with alcohol-containing beverages at social events. The aim of such a combination may be to use the stimulant properties of the energy drink to counteract the debilitating effects of alcohol intoxication. In fact, consumption of caffeine does increase alertness and counteract alcohol-related feelings of fatigue, even though users recognize that they are still alcohol intoxicated (Benson et al., 2014). Importantly, however, there is still alcohol-related impairment of complex psychomotor tasks (e.g., driving) despite caffeine consumption (Verster et al., 2012; McKetin et al., 2015). An additional problem is the increased tendency of young people to engage in risky behaviors, including risky driving, when combining alcohol with energy drinks (Striley and Khan, 2014).
In conclusion, the rapid growth of energy drink sales has caught the attention of researchers and policy makers alike. The studies reviewed above indicate that overconsumption of these beverages as well as use with alcohol can pose significant health risks. Children and adolescents are at particular risk for adverse reactions to energy drinks. This has led to increasing calls for more education about such risks and, in some countries, outright restrictions on the sale of energy drinks to minors (Oddy and O’Sullivan, 2010; Committee on Nutrition and the Council on Sports Medicine and Fitness, 2011).
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