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Energy Beverages: Content and Safety

      Exercise is making a resurgence in many countries, given its benefits for fitness as well as prevention of obesity. This trend has spawned many supplements that purport to aid performance, muscle growth, and recovery. Initially, sports drinks were developed to provide electrolyte and carbohydrate replacement. Subsequently, energy beverages (EBs) containing stimulants and additives have appeared in most gyms and grocery stores and are being used increasingly by “weekend warriors” and those seeking an edge in an endurance event. Long-term exposure to the various components of EBs may result in significant alterations in the cardiovascular system, and the safety of EBs has not been fully established. For this review, we searched the MEDLINE and EMBASE databases from 1976 through May 2010, using the following keywords: energy beverage, energy drink, power drink, exercise, caffeine, red bull, bitter orange, glucose, ginseng, guarana, and taurine. Evidence regarding the effects of EBs is summarized, and practical recommendations are made to help in answering the patient who asks, “Is it safe for me to drink an energy beverage when I exercise?”
      EB (energy beverage), ECG (electrocardiogram), SD (sport drink)
      Red Bull was introduced in Austria in 1987 and in the United States in 1997. Since then, the energy beverage (EB) market has grown exponentially.
      • Reissig CJ
      • Strain EC
      • Griffiths RR
      Caffeinated energy drinks—a growing problem.
      Hundreds of different brands are now marketed, with caffeine content ranging from a modest 50 mg to an alarming 505 mg per can or bottle.
      • Weise E
      Petition calls for FDA to regulate energy drinks.
      In the United States, Red Bull enjoyed a 65% share of the $650-million energy/power drink market in 2005, and its sales are growing at about 35% per year.
      • Bryce DJ
      • Dyer JH
      Strategies to crack well-guarded markets.
      The United States is the world's largest consumer of EBs by volume, roughly 290 million gallons in 2007, or 3.8 qt per person per year.
      • Weise E
      Petition calls for FDA to regulate energy drinks.
      Consumption of EBs is most common among those aged 11 to 35 years, and 24% to 57% of this age group reported that they drank an EB within the past few months.
      • Ballard SL
      • Wellborn-Kim JJ
      • Clauson KA
      Effects of commercial energy drink consumption on athletic performance and body composition.
      Regulation of EBs, including content labeling and health warnings, differs across countries, with some of the laxest requirements existing in the United States.
      • Weise E
      Petition calls for FDA to regulate energy drinks.
      For instance, no EBs are banned in the United States, and EB companies can say whatever they want regarding energy and performance effects. This is in stark contrast to countries in which some EBs have been banned, and companies are not allowed to outline the performance effects that their products may or may not provide.
      • Ballard SL
      • Wellborn-Kim JJ
      • Clauson KA
      Effects of commercial energy drink consumption on athletic performance and body composition.
      This absence of oversight has resulted in aggressive marketing of EBs, targeted primarily toward young men and openly promoting psychoactive, performance-enhancing, and stimulatory effects.
      • Reissig CJ
      • Strain EC
      • Griffiths RR
      Caffeinated energy drinks—a growing problem.
      • Ballard SL
      • Wellborn-Kim JJ
      • Clauson KA
      Effects of commercial energy drink consumption on athletic performance and body composition.
      Alarmingly, EB consumption has been shown to be positively associated with high-risk behavior, including marijuana use, sexual risk taking, fighting, failure to use seat belts, and taking risks on a dare, as well as with smoking, drinking, problems stemming from alcohol abuse, and illicit drug use.
      • Thombs DL
      • O'Mara RJ
      • Tsukamoto M
      • et al.
      Event-level analyses of energy drink consumption and alcohol intoxication in bar patrons.
      • Miller KE
      Energy drinks, race, and problem behaviors among college students.
      In an era in which Gatorade and Powerade, termed sport drinks (SDs) for the purposes of this article, have paved the way as optimal hydration fluids that boast superiority to water, uncertainty is growing with regard to where EBs fit and how they are consumed.
      • Howarth KR
      • Moreau NA
      • Phillips SM
      • Gibala MJ
      Coingestion of protein with carbohydrate during recovery from endurance exercise stimulates skeletal muscle protein synthesis in humans.
      Convenience stores now display EBs next to the SDs, which can mislead the consumer into thinking that they are similar products. Whereas SDs can indeed provide hydration and replenishment of electrolytes and carbohydrates, the elevated levels of caffeine in EBs have diuretic effects, more pronounced in the first-time user, that increase urinary output and natriuresis.
      • Riesenhuber A
      • Boehm M
      • Posch M
      • Aufricht C
      Diuretic potential of energy drinks.
      Additionally, EBs may have thermogenic effects.
      • Rashti SL
      • Ratamess NA
      • Kang J
      • Faigenbaum AD
      • Chilakos A
      • Hoffman JR
      Thermogenic effect of meltdown RTD energy drink in young healthy women: a double blind, cross-over design study.
      Moreover, EBs supply an amount of carbohydrate far beyond that recommended for physically active people, which can slow the rate at which fluid is absorbed into the bloodstream or lead to gastrointestinal distress.
      • Davis JM
      • Burgess WA
      • Slentz CA
      • Bartoli WP
      • Pate RR
      Effects of ingesting 6% and 12% glucose/electrolyte beverages during prolonged intermittent cycling in the heat.
      Finally, the effects due to the interaction of substances on which little research has been done (eg, glucuronolactone) are not well understood.
      This review of EBs describes the various ingredients, discusses their safety, and provides recommendations regarding their use. Although most research studies and observational data have come from athletics, our research query included studies and information involving nonathlete consumers. Also, the review differentiates between these populations and offers recommendations specific to each group.

      METHODS

      A search of the English-language scientific literature was performed primarily by searching the MEDLINE and EMBASE databases and using the Google Internet search engine for the period January 1976 through May 2010. For this search, we used keywords found in lead peer-reviewed articles and research outlining the current body of knowledge on EBs. Keywords used in the search are energy beverage, energy drink, power drink, exercise, caffeine, red bull, bitter orange, glucose, ginseng, guarana, and taurine. The bibliographies of articles were searched for relevant articles; links on Web sites containing published articles were searched for pertinent information. This review endeavored to bring the most pertinent research to light in order to present real-world recommendations to both the athletic community and the general population.

      INGREDIENTS OF EBs

      The most common ingredient in EBs is caffeine, which is often combined with taurine, glucuronolactone, guarana, and B vitamins to form what manufacturers have called an “energy blend.”
      • Reissig CJ
      • Strain EC
      • Griffiths RR
      Caffeinated energy drinks—a growing problem.
      When higher doses of caffeine are combined with these other substances currently blended in EBs, the subsequent effect cannot always be predicted; adverse effects have been reported, including cardiac arrest.
      • Berger AJ
      • Alford K
      Cardiac arrest in a young man following excess consumption of caffeinated “energy drinks.”.
      • Nagajothi N
      • Khraisat A
      • Velazquez-Cecena JL
      • et al.
      Energy drink-related supraventricular tachycardia.
      The components of the 4 best-selling EBs are given in Table 1, and the specific ingredients are subsequently discussed in more detail.
      TABLE 1Comparison of Ingredients in Energy Beverages
      As listed on 16-oz can unless otherwise noted. RDA = recommended daily allowance.
      Red BullRockstarMonsterFull Throttle
      Calories220280200220
      Carbohydrates
      • 54 g
      • Sucrose, glucose
      • 62 g
      • Sucrose, glucose
      • 54 g
      • Sucrose, glucose, sucralose, maltodextrin
      • 57 g
      • High-fructose corn syrup, sucrose
      SodiumOnly listed as sodium citrate80 mg sodium citrate
      • 360 mg
      • 16% RDA
      • Sodium citrate, sodium chloride
      160 mg Sodium citrate
      Caffeine160 mg
      • 160 mg
      • Part of a 1.35-g “energy blend”
      Only listed as part of a 5000-mg “energy blend”
      • 141 mg
      • Part of a 3000-mg “energy blend”
      Taurine2000 mg
      • 2000 mg
      • Part of a 1.35-g “energy blend”
      • 2000 mg
      • Part of a 5000-mg “energy blend”
      Only listed as part of a 3000-mg “energy blend”
      GlucuronolactoneOnly listed (1200 mg)
      This amount is not listed on the can; the corporate office was called and this was all the information given.
      None listedOnly listed as part of a 5000-mg “energy blend”None listed
      Niacin (B3)200% RDA Niacinamide (40 mg)
      This amount is not listed on the can; the corporate office was called and this was all the information given.
      40 mg 200% RDA Niacinamide40 mg 200% RDA Niacinamide100% RDA Niacinamide
      Inositol (B8)Only listed
      • 50 mg
      • Part of a 1.35-g “energy blend”
      Only listed as part of a 5000-mg “energy blend”None listed
      • Pyridoxine hydrochloride (B6)
      500% RDA (10 mg)
      This amount is not listed on the can; the corporate office was called and this was all the information given.
      4 mg 200% RDA4 mg 200% RDA200% RDA
      Cyanocobalamin (B)
      • 160% RDA
      • Listed as vitamin B12 (10μg)
        This amount is not listed on the can; the corporate office was called and this was all the information given.
      12 Hg 200% RDA12 Hg 200% RDA200% RDA
      Riboflavin (B2)None listed6.8 mg 400% RDA3.4 mg 200% RDANone listed
      Pantothenic acid (Bs)
      • 100% RDA
      • Calcium pantothenate (10 mg)
        This amount is not listed on the can; the corporate office was called and this was all the information given.
      20 mg 200% RDA Calcium pantothenateNone listedNone listed
      Ginseng extractNone listed
      • 50 mg
      • Part of a 1.35-g “energy blend”
      400 mgOnly listed as part of a 3000-mg “energy blend”
      Guarana extractNone listed
      • 50 mg
      • Part of a 1.35-g “energy blend”
      Only listed as part of a 5000-mg “energy blend”Only listed as part of a 3000-mg “energy blend”
      Ginkgo biloba leaf extractNone listed
      • 300 mg
      • Part of a 1.35-g “energy blend”
      None listedNone listed
      Milk thistle extractNone listed
      • 40 mg
      • Part of a 1.35-g “energy blend”
      None listedNone listed
      l-carnitineNone listed
      • 50 mg
      • Part of a 1.35-g “energy blend”
      Only listed as part of a 5000-mg “energy blend”
      • Only listed as part of a 3000-mg “energy blend”
      • Carnitine fumarate
      Sorbic acidNone listedYesYesNo
      Sodium benzoateNone listedYes Benzoic acidYes Benzoic acidYes
      Citric acidNone listedYesYesYes
      Natural flavorsYesYesYesYes
      Artificial flavorsYesYesNone listedNone listed
      Coloring“Colors”“Caramel”“Color added”Blue 1, Red 40
      a As listed on 16-oz can unless otherwise noted. RDA = recommended daily allowance.
      b This amount is not listed on the can; the corporate office was called and this was all the information given.
      Well-performed research indicates that some of these substances are important for proper body function, but this does not mean that a person has a deficiency. Moreover, important questions regarding overall intake and subsequent adverse effects should come to mind as the reader progresses through this review. We have also included information on the bioavailability of each substance if the necessary research has been completed.

      Caffeine

      Caffeine, an adenosine receptor antagonist, is a stimulant that can influence the activity of neuronal control pathways in the central and peripheral nervous systems.
      • Jones G
      Caffeine and other sympathomimetic stimulants: modes of action and effects on sports performance.
      It is the most common stimulant in EBs, with most EBs containing between 70 and 200 mg of caffeine per 16-oz serving. In comparison, an 8-oz cup of coffee contains 110 to 150 mg for drip, 65 to 125 mg for percolated, and 40 to 80 mg for instant; caffeinated beverages contain about 50 to 100 mg of caffeine.
      • Clauson KA
      • Shields KM
      • McQueen CE
      • Persad N
      Safety issues associated with commercially available energy drinks.
      Caffeine is known as an ergogenic compound that raises the heart rate and blood pressure. Adverse effects typically manifest with ingestion higher than 200 mg of caffeine and include insomnia, nervousness, headache, tachycardia, arrhythmia, and nausea.
      • Clauson KA
      • Shields KM
      • McQueen CE
      • Persad N
      Safety issues associated with commercially available energy drinks.
      • Calamaro CJ
      • Mason TB
      • Ratcliffe SJ
      Adolescents living the 24/7 lifestyle: effects of caffeine and technology on sleep duration and daytime functioning.
      The ergogenic effects of caffeine on athletic performance have been shown, and its broad range of metabolic, hormonal, and physiologic effects has been described.
      • Ganio MS
      • Klau JF
      • Casa DJ
      • Armstrong LE
      • Maresh CM
      Effect of caffeine on sport-specific endurance performance: a systematic review.
      • Sokmen B
      • Armstrong LE
      • Kraemer WJ
      • et al.
      Caffeine use in sports: considerations for the athlete.
      Caffeine has been shown to be an effective ergogenic aid for endurance athletes when ingested before and/or during exercise in moderate quantities (3-6 mg/kg of body mass); abstaining from caffeine for at least 7 days before use will optimize the effect.
      • Ganio MS
      • Klau JF
      • Casa DJ
      • Armstrong LE
      • Maresh CM
      Effect of caffeine on sport-specific endurance performance: a systematic review.
      Of note, caffeine appears on the list of substances banned by the International Olympic Committee.
      • Clarkson PM
      Nutrition for improved sports performance: current issues on ergogenic aids.
      Of all the compounds analyzed in this review, caffeine is by far the most-researched in the literature.
      • Ganio MS
      • Klau JF
      • Casa DJ
      • Armstrong LE
      • Maresh CM
      Effect of caffeine on sport-specific endurance performance: a systematic review.
      The absolute bioavailability of orally administered caffeine was investigated in 10 healthy adult male volunteers aged 19 to 30 years.
      • Blanchard J
      • Sawers SJ
      The absolute bioavailability of caffeine in man.
      Participants received a 5-mg/kg dose of caffeine as either an aqueous oral solution or an intravenous infusion on separate occasions about 1 week apart in a randomized crossover fashion. Plasma samples were collected during the 24-hour period after each dose and assayed for their caffeine content using a high-performance liquid chromatographic technique. The oral absorption was very rapid, with caffeine reaching a peak plasma concentration after 29.8 minutes, and the variation in the maximum plasma concentration was low at 10.0 μg/mL. The absolute bioavailability was assessed by comparing the areas under the plasma concentration vs time curves for the intravenous and oral doses of caffeine. The rapid absorption resulted in essentially complete bioavailability of the oral caffeine, with a plasma half-life varying from 2.7 to 9.9 hours, indicating substantial variability in its elimination between participants.
      • Blanchard J
      • Sawers SJ
      The absolute bioavailability of caffeine in man.
      Caffeine mobilizes fat stores and stimulates working muscles to use fat as a fuel, which delays depletion of muscle glycogen and allows for prolonged exercise.
      • Laurent D
      • Schneider KE
      • Prusaczyk WK
      • et al.
      Effects of caffeine on muscle glycogen utilization and the neuroendocrine axis during exercise.
      The critical period in glycogen sparing appears to occur during the first 15 minutes of exercise, when caffeine has been shown to decrease glycogen utilization by as much as 50%. Thus, glycogen saved at the beginning is available during the later stages of exercise. Although the exact mechanism is still unclear, caffeine caused sparing in all the human studies in which muscle glycogen levels were measured. The effect on performance, which was observed in most experimental studies, was that participants were able to exercise longer before exhaustion occurred.
      • Laurent D
      • Schneider KE
      • Prusaczyk WK
      • et al.
      Effects of caffeine on muscle glycogen utilization and the neuroendocrine axis during exercise.
      Caffeine binds to the adenosine class of G protein–coupled receptors on the surface of heart muscle cells, which begins a second messenger system with cyclic adenosine monophosphate inside the cells and mimics the effects of epinephrine.

      Piirainen H, Ashok Y, Nanekar RT, Jaakola VP. Structural features of adenosine receptors: from crystal to function [published online ahead of print June 2, 2010]. Biochim Biophys Acta. doi:10.1016/j.bbamem.2010.05.021.

      The rate of glycolysis increases, which increases the amount of adenosine triphosphate available for muscle contraction and relaxation.

      Mayo Clinic Staff. Nutrition and healthy eating: caffeine: how much is too much? MayoClinic.com Web site. Published March 24, 2009. http://www.mayoclinic.com/health/caffeine/NU00600#. Accessed September 3, 2010.

      This can result in a positive inotropy and chronotropy, ie, a stronger and faster heartbeat. Caffeine immediately increases blood pressure and peripheral vascular resistance, in part because of sympathetic stimulation. One group of investigators showed a significant effect of drinking caffeinated coffee on arterial tone and function, suggesting that caffeine immediatelyincreases arterial stiffness, with the effect being more pronounced on aortic systolic and diastolic blood pressures than on the brachial artery.
      • Mahmud A
      • Feely J
      Acute effect of caffeine on arterial stiffness and aortic pressure waveform.
      The discussion on caffeine and hydration continues to evolve. A number of studies have examined the effects of ingesting a large dose of caffeine and found that urine output was increased.
      • Neuhäuser-Berthold B
      • Beine S
      • Verwied SC
      • Lührmann PM
      Coffee consumption and total body water homeostasis as measured by fluid balance and bioelectrical impedance analysis.
      Yet, the long-held conclusion that caffeine increases 24-hour urine output has been challenged, because most of the studies that established this conclusion involved persons who refrained from caffeine consumption before the analysis.
      • Maughan RJ
      • Griffin J
      Caffeine ingestion and fluid balance: a review.
      • Robertson D
      • Wade D
      • Workman R
      • Woosley RL
      • Oates JA
      Tolerance to the humoral and hemodynamic effects of caffeine in man.
      The human body develops a tolerance to caffeine quickly, usually 3 to 5 days after regular use, and when this happens, it noticeably weakens the already limited diuretic effect of caffeine.
      • Robertson D
      • Wade D
      • Workman R
      • Woosley RL
      • Oates JA
      Tolerance to the humoral and hemodynamic effects of caffeine in man.
      • Fisher SM
      • McMurray RG
      • Berry M
      • Mar MH
      • Forsythe WA
      Influence of caffeine on exercise performance in habitual caffeine users.
      Moreover, the human kidneys are masters at ensuring that proper homeostatic conditions are maintained. Recent research now leans toward the ability of the body to maintain proper water levels and overcome the mild diuretic effects of caffeine in long-term users.
      • Maughan RJ
      • Griffin J
      Caffeine ingestion and fluid balance: a review.
      • Armstrong LE
      • Pumerantz AC
      • Roti MW
      • et al.
      Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption.
      As the rest of the ingredients are reviewed herein, please note that in comparison with caffeine, each has had far fewer research studies performed.

      Taurine

      Taurine, a sulfur-containing amino acid, is the most abundant intracellular amino acid in humans and a normal constituent of the human diet.
      • Gaull GE
      Taurine in pediatric nutrition: review and update.
      A study of the pharmacokinetics of taurine was conducted in 8 healthy male volunteers with a median age of 28 years. After oral administration of 4 g of taurine in the fasting state, blood samples were taken at regular intervals, and plasma taurine concentration was measured by a modified high-performance liquid chromatographic technique. Maximum plasma taurine concentration was 86 mg/L 1.5 hours after administration. Plasma elimination half-life and the ratio of clearance to bioavailability were 1.0 hour and 21 L/h, respectively.
      • Ghandforoush-Sattari M
      • Mashayekhi S
      • Krishna CV
      • Thompson JP
      • Routledge PA
      Pharmacokinetics of oral taurine in healthy volunteers.
      Taurine modulates skeletal muscle contractile function and may attenuate exercise-induced DNA damage, with some evidence showing the ability to improve exercise capacity and performance; however, this has not been definitively demonstrated.
      • Ballard SL
      • Wellborn-Kim JJ
      • Clauson KA
      Effects of commercial energy drink consumption on athletic performance and body composition.
      Taurine has numerous other biological and physiologic functions, including bile acid conjugation and cholestasis prevention; antiarrhythmic, inotropic, and chronotropic effects; central nervous system neuromodulation; retinal development and function; endocrine or metabolic effects; and antioxidant and anti-inflammatory properties.
      • Lourenço R
      • Camilo ME
      Taurine: a conditionally essential amino acid in humans? An overview in health and disease.
      Taurine also assists in cell membrane stabilization, osmoregulation, and detoxification.
      • Sato S
      • Kurasaki M
      The physiological role of taurine in tissues and organs, especially in the liver and kidney.
      However, the amounts of taurine found in popular EBs are far below the amounts expected to deliver either therapeutic benefits or adverse events.
      • Clauson KA
      • Shields KM
      • McQueen CE
      • Persad N
      Safety issues associated with commercially available energy drinks.

      Glucuronolactone

      This is a naturally occurring substance produced in small amounts within the body. Supplementation with D-glucarates, including glucuronolactone, may favor the body's natural defense mechanism for eliminating carcinogens and tumor promoters and their effects.
      • Zółtaszek R
      • Hanausek M
      • Kiliańska ZM
      • Walaszek Z
      The biological role of D-glucaric acid and its derivatives: potential use in medicine [in Polish].
      Toxicokinetic data on glucuronolactone in rats, which show bioavailability and lack of accumulation, with peak plasma levels 1 to 2 hours after oral administration, are in accordance with the limited human data.
      • Scientific Committee on Food
      European Commission, Health & Consumer Protection Directorate-General. Opinion of the Scientific Committee on Food on additional information on “energy” drinks. Published March 5, 2003.
      Unfortunately, little research has been done in humans, and the current body of knowledge on this substance is scant. Therefore, conclusions on whether this compound is harmful or beneficial cannot be made.

      B Vitamins

      The B vitamins are water-soluble vitamins required as coenzymes for proper cell function, especially mitochondrial function and energy production.
      • Depeint F
      • Bruce WR
      • Shangari N
      • Mehta R
      • O'Brien PJ
      Mitochondrial function and toxicity: role of the B vitamin family on mitochondrial energy metabolism.
      B vitamins include thiamine, riboflavin, niacin, pantothenic acid, pyridoxine hydrochloride, biotin, inositol, and cyanocobalamin. Because EBs contain large amounts of sugar, these vitamins are touted as ingredients necessary to convert the added sugar to energy. Hence, the B vitamins are the “key” needed to unlock all the energy provided by the simple sugars in EBs, and this is the extra energy that EB companies claim their product can provide. An expansive amount of research has been done on the B vitamins, and we outline the specific functions each major B vitamin plays in the human body.
      Thiamine (vitamin B1) is essential for the oxidative decarboxylation of the multienzyme branched-chain α-keto acid dehydrogenase complexes of the citric acid cycle and thus serves as a coenzyme precursor of some key enzymes of carbohydrate metabolism.
      • Ba A
      Metabolic and structural role of thiamine in nervous tissues.
      Riboflavin (vitamin B2) is required for the flavoenzymes of the respiratory chain and thus also supports energy metabolism involving fats, carbohydrates, and proteins.
      • Lakshmi AV
      Riboflavin metabolism–relevance to human nutrition.
      The reduced form of nicotinamide adenine dinucleotide (NADH) is synthesized from niacin (vitamin B3). This coenzyme is required to supply protons for oxidative phosphorylation and plays a major part in energy production in cells.
      • Sauve AA
      NAD+ and vitamin B3: from metabolism to therapies.
      It also stimulates the production of such neurotransmitters as l-dopa, dopamine, serotonin, and norepinephrine.
      Pantothenic acid (vitamin B5) is required for coenzyme A, α-ketoglutarate, and pyruvate dehydrogenase formation, as well as fatty acid oxidation.
      • Depeint F
      • Bruce WR
      • Shangari N
      • Mehta R
      • O'Brien PJ
      Mitochondrial function and toxicity: role of the B vitamin family on mitochondrial energy metabolism.
      Pyridoxine hydrochloride (vitamin B6) is a coenzyme involved in amino acid and homocysteine metabolism, glucose and lipid metabolism, neurotransmitter production, and DNA and RNA synthesis.
      • Spinneker A
      • Sola R
      • Lemmen V
      • Castillo MJ
      • Pietrzik K
      • Gonzalez-Gross M
      Vitamin B6 status, deficiency and its consequences—an overview.
      Specifically, pyridoxine hydrochloride is involved in protein and red blood cell metabolism, is important for immune system function, and is needed to convert tryptophan to niacin.
      Biotin (vitamin B7) is the coenzyme of decarboxylases required for gluconeogenesis and fatty acid oxidation.
      • Depeint F
      • Bruce WR
      • Shangari N
      • Mehta R
      • O'Brien PJ
      Mitochondrial function and toxicity: role of the B vitamin family on mitochondrial energy metabolism.
      Inositol (formerly vitamin B8 but declassified as a vitamin because it is synthesized by the human body) exists in 9 possible stereoisomers, of which the most common form is myo-inositol. It is part of cell membranes, plays a role in helping the liver process fats, and contributes to the function of muscles and nerves.
      • Balla T
      Regulation of Ca2+ entry by inositol lipids in mammalian cells by multiple mechanisms.
      Cyanocobalamin (vitamin B12) helps maintain nerve cell function, is needed for production of DNA, and is important in red blood cell formation.
      • Depeint F
      • Bruce WR
      • Shangari N
      • Mehta R
      • O'Brien PJ
      Mitochondrial function and toxicity: role of the B vitamin family on mitochondrial energy metabolism.

      Guarana

      Also known as guaranine, Paullinia cupana, and Sapindaceae, guarana is a rainforest vine that was domesticated in the Amazon for its caffeine-rich fruits and has long been used by the Amazonians to increase awareness and energy.
      • da Costa Miranda V
      • Trufelli DC
      • Santos J
      • et al.
      Effectiveness of guarana (Paullinia cupana) for postradiation fatigue and depression: results of a pilot double-blind randomized study.
      Guarana seeds contain more caffeine than any other plant in the world, with levels ranging from 2% to 8%; guarana also contains the stimulants theobromine and theophylline.
      • Smith N
      • Atroch AL
      Guaraná's journey from regional tonic to aphrodisiac and global energy drink.
      The amounts of guarana found in popular EBs are below the amounts expected to deliver therapeutic benefits or cause adverse events.
      • Clauson KA
      • Shields KM
      • McQueen CE
      • Persad N
      Safety issues associated with commercially available energy drinks.
      However, some young adults have been admitted to emergency departments with overdoses of caffeine after overindulging in guarana-based EBs.
      • Smith N
      • Atroch AL
      Guaraná's journey from regional tonic to aphrodisiac and global energy drink.

      Ginseng

      Ginseng is one of the most popular herbal supplements in the world and is used for treatment and prevention of many ailments. This adaptogen (a natural herb product said to increase the body's resistance to stress, trauma, anxiety, and fatigue) is purported to increase energy, relieve stress, and increase memory by stimulating the hypothalamic and pituitary glands to secrete corticotropin. Athletes use ginseng for its alleged performance-enhancing attributes; however, a recent review concluded that enhanced physical performance after ginseng administration remains to be demonstrated.
      • Bahrke MS
      • Morgan WP
      • Stegner A
      Is ginseng an ergogenic aid?.
      Adverse effects associated with ginseng include hypotension, edema, palpitations, tachycardia, cerebral arteritis, vertigo, headache, insomnia, mania, vaginal bleeding, amenorrhea, fever, appetite suppression, pruritus, cholestatic hepatitis, mastalgia, euphoria, and neonatal death.
      • Ballard SL
      • Wellborn-Kim JJ
      • Clauson KA
      Effects of commercial energy drink consumption on athletic performance and body composition.
      However, the amounts of ginseng found in EBs are far below the amounts expected to deliver therapeutic benefits or cause adverse events.
      • Clauson KA
      • Shields KM
      • McQueen CE
      • Persad N
      Safety issues associated with commercially available energy drinks.

      Ginkgo Biloba

      Ginkgo biloba extract is derived from the leaves of the Ginkgo biloba tree and has been used in traditional Chinese medicine for centuries.
      • Nicolaï SP
      • Kruidenier LM
      • Bendermacher BL
      • Prins MH
      • Teijink JA
      Ginkgo biloba for intermittent claudication.
      Ginkgo biloba extract has been reported to have antioxidant properties, modify vasomotor function, reduce adhesion of blood cells to endothelium, inhibit activation of platelets and smooth muscle cells, affect ion channels, and alter signal transduction.
      • Zhou W
      • Chai H
      • Lin PH
      • Lumsden AB
      • Yao Q
      • Chen C
      Clinical use and molecular mechanisms of action of extract of Ginkgo biloba leaves in cardiovascular diseases.
      However, to date, no large, well-conducted randomized controlled trials have shown that it has important clinical effects in healthy or ill persons.
      • Nicolaï SP
      • Kruidenier LM
      • Bendermacher BL
      • Prins MH
      • Teijink JA
      Ginkgo biloba for intermittent claudication.

      l-Carnitine

      This amino acid is made predominantly by the liver and kidneys to increase metabolism. Dietary supplementation with l-carnitine has been shown to increase maximal oxygen consumption and lower the respiratory quotient, indicating stimulation of lipid metabolism.
      • Karlic H
      • Lohninger A
      Supplementation of L-carnitine in athletes: does it make sense?.
      Recent evidence indicates that l-carnitine plays a decisive role in preventing cellular damage and favorably affects recovery from exercise stress. Uptake of l-carnitine by blood cells may promote (1) stimulation of hematopoiesis, (2) inhibition of collagen-induced platelet aggregation, and (3) prevention of programmed cell death in immune cells. There is evidence of a beneficial effect of l-carnitine supplementation in training, competition, and recovery from strenuous exercise and in regenerative athletics.
      • Karlic H
      • Lohninger A
      Supplementation of L-carnitine in athletes: does it make sense?.
      No advantage appears to exist in giving an oral dose greater than 2 g at one time, because absorption studies indicate saturation at this dose.
      • Bain MA
      • Milne RW
      • Evans AM
      Disposition and metabolite kinetics of oral L-carnitine in humans.

      Sugars

      Sugars are the basic currency for energy in the body, with glucose being the key carbohydrate that can readily be oxidized by skeletal muscle for energy production. Often, EBs contain sugar (high-fructose corn syrup or sucrose). Administration of glucose or other carbohydrates before, during, and after prolonged exercise (>1 hour) has been shown to postpone fatigue, conserve muscle glycogen, and improve performance.
      • el-Sayed MS
      • MacLaren D
      • Rattu AJ
      Exogenous carbohydrate utilisation: effects on metabolism and exercise performance.
      • Burke LM
      • Millet G
      • Tarnopolsky MA
      • International Association of Athletics Federations
      Nutrition for distance events [published correction appears in J Sports Sci. 2009;27(6):667].
      Ingestion of moderately concentrated carbohydrate solutions (4%-8%) with the aim of achieving a carbohydrate intake of 60 to 70 g/h enhances prolonged exercise performance and is appropriate for optimizing energy and fluid delivery without causing adverse effects.
      • Jeukendrup AE
      • Jentjens RL
      • Moseley L
      Nutritional considerations in triathlon.
      However, the ergogenic effects of carbohydrate ingestion on performance during intermittent exercise such as competitive sports are less well established, although the evidence to date suggests diminished performance when carbohydrates are limited.
      • el-Sayed MS
      • MacLaren D
      • Rattu AJ
      Exogenous carbohydrate utilisation: effects on metabolism and exercise performance.
      The amount of sugar provided in one can (or 500 mL) of an EB is typically about 54 g. A teaspoon of sugar weighs about 4 g, so a typical EB contains about 13 teaspoons, or just more than ¼ cup, of sugar.
      Long-term exposure of the body to excesses of simple sugars is associated with the development of obesity and insulin resistance. Pancreatic beta cells increase insulin secretion in response to this reduction in insulin sensitivity. Over time, in many individuals, the beta cells become unable to secrete sufficient insulin to maintain normal blood glucose levels, leading to the development of diabetes.

      Tappy L, Lê KA, Tran C, Paquot N. Fructose and metabolic diseases: new findings, new questions [published online ahead of print May 13, 2010]. Nutrition. doi:10.1016/j.nut.2010.02.014.

      Antioxidants

      During exercise, inflammation and oxidative stress are linked by means of muscle metabolism and muscle damage.
      • Peake JM
      • Suzuki K
      • Coombes JS
      The influence of antioxidant supplementation on markers of inflammation and the relationship to oxidative stress after exercise.
      Antioxidants are purported to aid the body in the recovery phase and reduce damage to muscle cells.
      • Williams SL
      • Strobel NA
      • Lexis LA
      • Coombes JS
      Antioxidant requirements of endurance athletes: implications for health.
      However, there is no convincing evidence that short-term or long-term exercise modifies antioxidant requirements, nor have significant effects been shown for supplementation in well-trained athletes.
      • Margaritis I
      • Rousseau AS
      Does physical exercise modify antioxidant requirements?.

      DO EBs WORK AND ARE THEY SAFE?

      Research Issues

      A number of factors relating to EB consumption may make good morbidity and mortality data difficult to ascertain. These include the following.
      • The target market for EBs is people between 15 and 30 years of age. This population is typically healthy and involved in activities and includes a higher proportion of sports enthusiasts and high-risk takers.
      • Because of the many ingredients in EBs, cause and effect is difficult to assign to one specific ingredient. Indeed, it may be the combination of ingredients that augments the effect.
      • Most of the ingredients are available over the counter and are unregulated in the United States. Thus, EBs are not under the jurisdiction of the US Food and Drug Administration and therefore are not subject to the stringent requirements for safety and efficacy data before approval for human use.
      • Binge drinking of EBs combined with alcohol is common practice, again making causation difficult to assign.
      • Many people consume more than the recommended daily allowance of EBs. (Recommended daily allowance is one can.)

      Short-term Effects

      In addressing the question of safety, it is important to consider both short-term and long-term effects of ingestion of EBs. Physiologic effects occur immediately after drinking the first dose.
      In one study, 15 healthy persons aged 18 to 40 years consumed 2 cans (500 mL) of a commercially available EB containing 1000 mg of taurine and 100 mg of caffeine, as well as vitamins B5, B6, and B12, glucuronolactone, and niacinamide, daily for 1 week; effects of the EB on their blood pressure, pulse, and electrocardiogram (ECG) were measured.
      • Steinke L
      • Lanfear DE
      • Dhanapal V
      • Kalus JS
      Effect of “energy drink” consumption on hemodynamic and electrocardiographic parameters in healthy young adults.
      The key effects were as follows.
      • Within 4 hours of EB consumption, the maximum systolic blood pressure increased by 8% on day 1 and 10% on day 7.
      • Within 2 hours of EB consumption, the maximum diastolic blood pressure increased by 7% on day 1 and 8% on day 7.
      • Heart rate increased by 8% on day 1 and 11% on day 7.
      • Throughout the study, heart rates increased between 5 and 7 beats/min, and systolic blood pressure increased by 10 mm Hg after EB consumption.
      • No clinically important ECG changes were observed.
      The authors concluded that, although no clinically important ECG changes occurred, there were significant increases in heart rate and blood pressure, and thus patients with hypertension should not consume this type of drink.
      • Steinke L
      • Lanfear DE
      • Dhanapal V
      • Kalus JS
      Effect of “energy drink” consumption on hemodynamic and electrocardiographic parameters in healthy young adults.
      In a double-blind crossover study, 13 endurance-trained participants performed an exhaustive bout of endurance exercise at 3 different times.
      • Baum M
      • Weiss M
      The influence of a taurine containing drink on cardiac parameters before and after exercise measured by echocardiography.
      Before the exercise, they ingested the original Red Bull drink, a similar drink without taurine but containing caffeine, and a placebo drink without caffeine or taurine. Echocardiography was performed before ingestion of the drinks, before exercise, 40 minutes after ingestion, and in the recovery period after exercise. Stroke volume was significantly influenced only in the Red Bull group (80±21 mL before ingestion vs 98±26 mL in the recovery period), mainly because of reduced end-systolic volume. Thus, this study shows that the original Red Bull increases cardiac contractility.
      • Baum M
      • Weiss M
      The influence of a taurine containing drink on cardiac parameters before and after exercise measured by echocardiography.
      A double-blind study of 68 healthy college-aged students showed that Red Bull reduced the changes in blood pressure during a stressful experience (cold pressor test) and increased participants' pain threshold.
      • Ragsdale FR
      • Gronli TD
      • Batool N
      • et al.
      Effect of Red Bull energy drink on cardiovascular and renal function.
      In a study of the effects of EBs on high-intensity run time-to-exhaustion in physically active university students (n=17; 9 men; mean age, 21±4 years), sugar-free Red Bull did not influence high-intensity run time-to-exhaustion.
      • Candow DG
      • Kleisinger AK
      • Grenier S
      • Dorsch KD
      Effect of sugar-free Red Bull energy drink on high-intensity run time-to-exhaustion in young adults.
      However, in a study of 6 male and 6 female trained cyclists (mean age, 27.3 years), improved cycling time-trial performance was noted after ingestion of a caffeinated EB.
      • Ivy JL
      • Kammer L
      • Ding Z
      • et al.
      Improved cycling time-trial performance after ingestion of a caffeine energy drink.
      In addition to these studies, several case reports on the immediate effects of EB ingestion have been published.
      • Four documented cases of caffeine-associated death have been reported, as well as 5 separate cases of seizures associated with consumption of energy/power drinks.
        • Ballard SL
        • Wellborn-Kim JJ
        • Clauson KA
        Effects of commercial energy drink consumption on athletic performance and body composition.
        • Clauson KA
        • Shields KM
        • McQueen CE
        • Persad N
        Safety issues associated with commercially available energy drinks.
      • An otherwise healthy 28-year-old man had cardiac arrest after a day of motocross racing.
        • Berger AJ
        • Alford K
        Cardiac arrest in a young man following excess consumption of caffeinated “energy drinks.”.
      • A healthy 18-year-old man died playing basketball after drinking 2 cans of Red Bull.
        Independent.ie. Red Bull, alcohol and drugs ‘can spark violence.’ Published February 21, 2007.
      • Postural tachycardia syndrome associated with a vasovagal reaction was recorded in a young volleyball player after an excess intake of Red Bull as a refreshing energy/power drink, leading experts to suspect the drink as a possible cause of orthostatic intolerance.
        • Terlizzi R
        • Rocchi C
        • Serra M
        • Solieri L
        • Cortelli P
        Reversible postural tachycardia syndrome due to inadvertent overuse of Red Bull.
      • Four cases of psychiatric effects on patients with known psychiatric illness were reported.
        • Ballard SL
        • Wellborn-Kim JJ
        • Clauson KA
        Effects of commercial energy drink consumption on athletic performance and body composition.
      • One case of suspected anaphylaxis was reported.
        • Masuda K
        • Katoh N
        • Mizutani H
        • Kishimoto S
        Anaphylaxis to vitamin B2 added to an energy drink.
      Regarding fluid replacement in persons who do not typically ingest large amounts of caffeine, EBs deliver a considerable amount of caffeine, which can stimulate the kidneys to produce more urine. Thus, EBs can have a net dehydrating effect.
      • Hew-Butler T
      • Verbalis JG
      • Noakes TD
      Updated fluid recommendation: position statement from the International Marathon Medical Directors Association (IMMDA).

      Long-term Effects

      Unfortunately, there are no long-term studies of the effects of caffeine, taurine, and glucuronolactone on the body.
      • Ballard SL
      • Wellborn-Kim JJ
      • Clauson KA
      Effects of commercial energy drink consumption on athletic performance and body composition.
      Energy beverages may exacerbate risk factors for heart disease because studies suggest that EBs may serve as a gateway to other forms of drug dependence.
      • Reissig CJ
      • Strain EC
      • Griffiths RR
      Caffeinated energy drinks—a growing problem.
      Norway, Denmark, and France have banned the sale of Red Bull, partly in response to a study on rats that were fed taurine and exhibited bizarre behavior, including anxiety and self-mutilation.
      • CBC News
      Red Bull promotion near Halifax schools halted: energy drink maker tells province promotion was a mistake. Updated September 27, 2007.
      Whether caffeine can cause hypertension and coronary artery disease is still controversial, but questions have been raised about its safety in patients with heart failure and arrhythmia.
      • Frishman WH
      • Del Vecchio A
      • Sanal S
      • Ismail A
      Cardiovascular manifestations of substance abuse: part 2: alcohol, amphetamines, heroin, cannabis, and caffeine.
      However, no clear association between coffee and the risk of hypertension, myocardial infarction, or other cardiovascular diseases has been demonstrated.
      • Sudano I
      • Binggeli C
      • Spieker L
      • et al.
      Cardiovascular effects of coffee: is it a risk factor?.

      Combining EBs and Alcohol

      Many consumers are combining EBs with alcoholic drinks. These individuals are typically white men and intramural athletes, a group now termed “toxic jocks.”
      • Ballard SL
      • Wellborn-Kim JJ
      • Clauson KA
      Effects of commercial energy drink consumption on athletic performance and body composition.
      The consequences can be tragic, as illustrated recently by Cleveland Browns wide receiver Donté Stallworth, who told police that he drank up to 4 shots of premium tequila and a can of Red Bull while partying with friends at a Miami Beach club, but did not feel drunk in the hours before he struck and killed a pedestrian with his car.
      • Jones B
      Tapes reveal Stallworth had tequila, shots before fatal accident.
      The combination of EBs with alcohol can impair cognitive function and reduce symptoms of alcohol intoxication, including the depressant effects, thus increasing the probability of accidents and/or favoring the possibility of development of alcohol dependence.
      • Curry K
      • Stasio MJ
      The effects of energy drinks alone and with alcohol on neuropsychological functioning.
      • Oteri A
      • Salvo F
      • Caputi AP
      • Calapai G
      Intake of energy drinks in association with alcoholic beverages in a cohort of students of the School of Medicine of the University of Messina.
      The combination might also increase important arrhythmia in patients with underlying heart disease.
      • Wiklund U
      • Karlsson M
      • Ostrom M
      • Messner T
      Influence of energy drinks and alcohol on post-exercise heart rate recovery and heart rate variability.
      In late 2009, 100 scientists and physicians signed a petition that was delivered to the US Food and Drug Administration asking for more regulation of increasingly popular EBs because their high caffeine content puts young drinkersat possible risk of caffeine intoxication and higher rates of alcohol-related injuries.
      • Weise E
      Petition calls for FDA to regulate energy drinks.
      • Thombs DL
      • O'Mara RJ
      • Tsukamoto M
      • et al.
      Event-level analyses of energy drink consumption and alcohol intoxication in bar patrons.
      Clearly, more research is needed concerning the combined effects of the substances listed in this report and, specifically, at the doses EBs provide. Teens and young adults, both athletes and nonathletes, are consuming EBs at an alarming rate; thus, we need to determine whether long-term use of EBs by this population will translate into deleterious effects later.

      RECOMMENDATIONS

      On the basis of this review, we make the recommendations listed in Table 2.
      TABLE 2Recommendations Regarding Energy Beverage Consumption
      • For the nonathlete consumer
        • Limit your consumption of EBs to no more than 500 mL, or 1 can per day
        • Do not mix EBs with alcohol; this can mask intoxication and may be extremely dehydrating
        • Rehydrate with water or an appropriately formulated SD after exercise or intense physical activity
        • If you experience an adverse reaction to an EB, report it to your health care professional or organization
        • If you are being treated for hypertension, avoid using EBs
        • If you have a serious underlying medical condition, including coronary artery disease, heart failure, or arrhythmia, consult with your physician before using EBs
      • For the athlete participating in exercise lasting <1 h
        • Do not use EBs
        • SDs appear safe, but we recommend against EBs while exercising because of the possibility of dehydration, elevation of blood pressure, and lack of equivocal benefits vs water or SDs
      • For the athlete participating in exercise lasting ≥1 h
        • Do not use EBs
        • SDs containing carbohydrates and electrolytes help prevent dehydration and restore important minerals lost through perspiration, and they produce better hydration than water
      EB = energy beverage; SD = sport drink.
      In summary, one can of an EB during one session is safe for most healthy individuals. However, excess consumption and consumption with other caffeine-containing beverages or alcohol may lead to adverse effects and possibly death. Patients with clinically relevant underlying medical conditions, including heart disease and hypertension, should consult with their physician before drinking EBs.

      CONCLUSION

      Coaches and athletic departments should take the initiative in addressing the issue of EBs with student athletes and in educating them about the effects and risks. The main ingredients of energy/power drinks are caffeine, taurine, glucuronolactone, B vitamins, guarana, ginseng, ginkgo biloba, l-carnitine, sugars, antioxidants, and trace minerals. The negative effects of excess caffeine have been proven, but the positive effects of many of the other additives, such as taurine and glucuronolactone, remain unproven, as does the combined effect of these ingredients in EBs.
      Ingestion of EBs before an event or during training can have serious adverse effects, most notably restlessness and irritability; can increase blood pressure; and may result in dehydration. The long-term effects of EBs on the human body have not been established.
      Limited ingestion of EBs by healthy people is not likely to cause major adverse effects, but binge consumption or consumption with alcohol may lead to adverse events. Individuals with medical illnesses, especially underlying heart disease, should check with their physician before using EBs, because they may exacerbate their condition.

      REFERENCES

        • Reissig CJ
        • Strain EC
        • Griffiths RR
        Caffeinated energy drinks—a growing problem.
        Drug Alcohol Depend. 2009; 99: 1-10
        • Weise E
        Petition calls for FDA to regulate energy drinks.
        USA Today. October 22, 2008; (Accessed September 3, 2010.)
        • Bryce DJ
        • Dyer JH
        Strategies to crack well-guarded markets.
        Harv Bus Rev. 2007; 85: 84-92
        • Ballard SL
        • Wellborn-Kim JJ
        • Clauson KA
        Effects of commercial energy drink consumption on athletic performance and body composition.
        Phys Sportsmed. 2010; 38: 107-117
        • Thombs DL
        • O'Mara RJ
        • Tsukamoto M
        • et al.
        Event-level analyses of energy drink consumption and alcohol intoxication in bar patrons.
        Addict Behav. 2009; 35: 325-330
        • Miller KE
        Energy drinks, race, and problem behaviors among college students.
        J Adolesc Health. 2008; 43: 490-497
        • Howarth KR
        • Moreau NA
        • Phillips SM
        • Gibala MJ
        Coingestion of protein with carbohydrate during recovery from endurance exercise stimulates skeletal muscle protein synthesis in humans.
        J Appl Physiol. 2009; 106: 1394-1402
        • Riesenhuber A
        • Boehm M
        • Posch M
        • Aufricht C
        Diuretic potential of energy drinks.
        Amino Acids. 2006; 31: 81-83
        • Rashti SL
        • Ratamess NA
        • Kang J
        • Faigenbaum AD
        • Chilakos A
        • Hoffman JR
        Thermogenic effect of meltdown RTD energy drink in young healthy women: a double blind, cross-over design study.
        Lipids Health Dis. 2009; 8: 57
        • Davis JM
        • Burgess WA
        • Slentz CA
        • Bartoli WP
        • Pate RR
        Effects of ingesting 6% and 12% glucose/electrolyte beverages during prolonged intermittent cycling in the heat.
        Eur J Appl Physiol Occup Physiol. 1988; 57: 563-569
        • Berger AJ
        • Alford K
        Cardiac arrest in a young man following excess consumption of caffeinated “energy drinks.”.
        Med J Aust. 2009; 190: 41-43
        • Nagajothi N
        • Khraisat A
        • Velazquez-Cecena JL
        • et al.
        Energy drink-related supraventricular tachycardia.
        Am J Med. 2008; 121: e3-e4
        • Jones G
        Caffeine and other sympathomimetic stimulants: modes of action and effects on sports performance.
        Essays Biochem. 2008; 44: 109-123
        • Clauson KA
        • Shields KM
        • McQueen CE
        • Persad N
        Safety issues associated with commercially available energy drinks.
        J Am Pharm Assoc. 2008; 48 (2003): e55-e63
        • Calamaro CJ
        • Mason TB
        • Ratcliffe SJ
        Adolescents living the 24/7 lifestyle: effects of caffeine and technology on sleep duration and daytime functioning.
        Pediatrics. 2009; 123: e1005-e1010
        • Ganio MS
        • Klau JF
        • Casa DJ
        • Armstrong LE
        • Maresh CM
        Effect of caffeine on sport-specific endurance performance: a systematic review.
        J Strength Cond Res. 2009; 23: 315-324
        • Sokmen B
        • Armstrong LE
        • Kraemer WJ
        • et al.
        Caffeine use in sports: considerations for the athlete.
        J Strength Cond Res. 2008; 22: 978-986
        • Clarkson PM
        Nutrition for improved sports performance: current issues on ergogenic aids.
        Sports Med. 1996; 21: 393-401
        • Blanchard J
        • Sawers SJ
        The absolute bioavailability of caffeine in man.
        Eur J Clin Pharmacol. 1983; 24: 93-98
        • Laurent D
        • Schneider KE
        • Prusaczyk WK
        • et al.
        Effects of caffeine on muscle glycogen utilization and the neuroendocrine axis during exercise.
        J Clin Endocrinol Metab. 2000; 85: 2170-2175
      1. Piirainen H, Ashok Y, Nanekar RT, Jaakola VP. Structural features of adenosine receptors: from crystal to function [published online ahead of print June 2, 2010]. Biochim Biophys Acta. doi:10.1016/j.bbamem.2010.05.021.

      2. Mayo Clinic Staff. Nutrition and healthy eating: caffeine: how much is too much? MayoClinic.com Web site. Published March 24, 2009. http://www.mayoclinic.com/health/caffeine/NU00600#. Accessed September 3, 2010.

        • Mahmud A
        • Feely J
        Acute effect of caffeine on arterial stiffness and aortic pressure waveform.
        Hypertension. 2001; 38: 227-231
        • Neuhäuser-Berthold B
        • Beine S
        • Verwied SC
        • Lührmann PM
        Coffee consumption and total body water homeostasis as measured by fluid balance and bioelectrical impedance analysis.
        Ann Nutr Metab. 1997; 41: 29-36
        • Maughan RJ
        • Griffin J
        Caffeine ingestion and fluid balance: a review.
        J Hum Nutr Diet. 2003; 16: 411-420
        • Robertson D
        • Wade D
        • Workman R
        • Woosley RL
        • Oates JA
        Tolerance to the humoral and hemodynamic effects of caffeine in man.
        J Clin Invest. 1981; 67: 1111-1117
        • Fisher SM
        • McMurray RG
        • Berry M
        • Mar MH
        • Forsythe WA
        Influence of caffeine on exercise performance in habitual caffeine users.
        Int J Sports Med. 1986; 7: 276-280
        • Armstrong LE
        • Pumerantz AC
        • Roti MW
        • et al.
        Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption.
        Int J Sport Nutr Exerc Metab. 2005; 15: 252-265
        • Gaull GE
        Taurine in pediatric nutrition: review and update.
        Pediatrics. 1989; 83: 433-442
        • Ghandforoush-Sattari M
        • Mashayekhi S
        • Krishna CV
        • Thompson JP
        • Routledge PA
        Pharmacokinetics of oral taurine in healthy volunteers.
        J Amino Acids. 2010; (Accessed September 3, 2010.): 10
        • Lourenço R
        • Camilo ME
        Taurine: a conditionally essential amino acid in humans? An overview in health and disease.
        Nutr Hosp. 2002; 17: 262-270
        • Sato S
        • Kurasaki M
        The physiological role of taurine in tissues and organs, especially in the liver and kidney.
        Foods Food Ingred J Jpn. 2003; 208: 133-139
        • Zółtaszek R
        • Hanausek M
        • Kiliańska ZM
        • Walaszek Z
        The biological role of D-glucaric acid and its derivatives: potential use in medicine [in Polish].
        Postepy Hig Med Dosw (Online). 2008; 62: 451-462
        • Scientific Committee on Food
        European Commission, Health & Consumer Protection Directorate-General. Opinion of the Scientific Committee on Food on additional information on “energy” drinks. Published March 5, 2003.
        (Accessed September 3, 2010.)
        • Depeint F
        • Bruce WR
        • Shangari N
        • Mehta R
        • O'Brien PJ
        Mitochondrial function and toxicity: role of the B vitamin family on mitochondrial energy metabolism.
        Chem Biol Interact. 2006; 163: 94-112
        • Ba A
        Metabolic and structural role of thiamine in nervous tissues.
        Cell Mol Neurobiol. 2008; 28: 923-931
        • Lakshmi AV
        Riboflavin metabolism–relevance to human nutrition.
        Indian J Med Res. 1998; 108: 182-190
        • Sauve AA
        NAD+ and vitamin B3: from metabolism to therapies.
        J Pharmacol Exp Ther. 2008; 324: 883-893
        • Spinneker A
        • Sola R
        • Lemmen V
        • Castillo MJ
        • Pietrzik K
        • Gonzalez-Gross M
        Vitamin B6 status, deficiency and its consequences—an overview.
        Nutr Hosp. 2007; 22: 7-24
        • Balla T
        Regulation of Ca2+ entry by inositol lipids in mammalian cells by multiple mechanisms.
        Cell Calcium. 2009; 45: 527-534
        • da Costa Miranda V
        • Trufelli DC
        • Santos J
        • et al.
        Effectiveness of guarana (Paullinia cupana) for postradiation fatigue and depression: results of a pilot double-blind randomized study.
        J Altern Complement Med. 2009; 15: 431-433
        • Smith N
        • Atroch AL
        Guaraná's journey from regional tonic to aphrodisiac and global energy drink.
        Evid Based Complement Alternat Med. 2007; 5: 5
        • Bahrke MS
        • Morgan WP
        • Stegner A
        Is ginseng an ergogenic aid?.
        Int J Sport Nutr Exerc Metab. 2009; 19: 298-322
        • Nicolaï SP
        • Kruidenier LM
        • Bendermacher BL
        • Prins MH
        • Teijink JA
        Ginkgo biloba for intermittent claudication.
        Cochrane Database Syst Rev. 2009; (CD006888.)
        • Zhou W
        • Chai H
        • Lin PH
        • Lumsden AB
        • Yao Q
        • Chen C
        Clinical use and molecular mechanisms of action of extract of Ginkgo biloba leaves in cardiovascular diseases.
        Cardiovasc Drug Rev. 2004; 22: 309-319
        • Karlic H
        • Lohninger A
        Supplementation of L-carnitine in athletes: does it make sense?.
        Nutrition. 2004; 20: 709-715
        • Bain MA
        • Milne RW
        • Evans AM
        Disposition and metabolite kinetics of oral L-carnitine in humans.
        J Clin Pharmacol. 2006; 46: 1163-1170
        • el-Sayed MS
        • MacLaren D
        • Rattu AJ
        Exogenous carbohydrate utilisation: effects on metabolism and exercise performance.
        Comp Biochem Physiol Physiol. 1997; 118: 789-803
        • Burke LM
        • Millet G
        • Tarnopolsky MA
        • International Association of Athletics Federations
        Nutrition for distance events [published correction appears in J Sports Sci. 2009;27(6):667].
        J Sports Sci. 2007; 25: S29-S38
        • Jeukendrup AE
        • Jentjens RL
        • Moseley L
        Nutritional considerations in triathlon.
        Sports Med. 2005; 35: 163-181
      3. Tappy L, Lê KA, Tran C, Paquot N. Fructose and metabolic diseases: new findings, new questions [published online ahead of print May 13, 2010]. Nutrition. doi:10.1016/j.nut.2010.02.014.

        • Peake JM
        • Suzuki K
        • Coombes JS
        The influence of antioxidant supplementation on markers of inflammation and the relationship to oxidative stress after exercise.
        J Nutr Biochem. 2007; 18: 357-371
        • Williams SL
        • Strobel NA
        • Lexis LA
        • Coombes JS
        Antioxidant requirements of endurance athletes: implications for health.
        Nutr Rev. 2006; 64: 93-108
        • Margaritis I
        • Rousseau AS
        Does physical exercise modify antioxidant requirements?.
        Nutr Res Rev. 2008; 21: 3-12
        • Steinke L
        • Lanfear DE
        • Dhanapal V
        • Kalus JS
        Effect of “energy drink” consumption on hemodynamic and electrocardiographic parameters in healthy young adults.
        Ann Pharmacother. 2009; 43: 596-602
        • Baum M
        • Weiss M
        The influence of a taurine containing drink on cardiac parameters before and after exercise measured by echocardiography.
        Amino Acids. 2001; 20: 75-82
        • Ragsdale FR
        • Gronli TD
        • Batool N
        • et al.
        Effect of Red Bull energy drink on cardiovascular and renal function.
        Amino Acids. 2010; 38: 1193-1200
        • Candow DG
        • Kleisinger AK
        • Grenier S
        • Dorsch KD
        Effect of sugar-free Red Bull energy drink on high-intensity run time-to-exhaustion in young adults.
        J Strength Cond Res. 2009; 23: 1271-1275
        • Ivy JL
        • Kammer L
        • Ding Z
        • et al.
        Improved cycling time-trial performance after ingestion of a caffeine energy drink.
        Int J Sport Nutr Exerc Metab. 2009; 19: 61-78
      4. Independent.ie. Red Bull, alcohol and drugs ‘can spark violence.’ Published February 21, 2007.
        (Accessed September 3, 2010.)
        • Terlizzi R
        • Rocchi C
        • Serra M
        • Solieri L
        • Cortelli P
        Reversible postural tachycardia syndrome due to inadvertent overuse of Red Bull.
        Clin Auton Res. 2008; 18: 221-223
        • Masuda K
        • Katoh N
        • Mizutani H
        • Kishimoto S
        Anaphylaxis to vitamin B2 added to an energy drink.
        Clin Exp Dermatol. 2009; 34: e263-e264
        • Hew-Butler T
        • Verbalis JG
        • Noakes TD
        Updated fluid recommendation: position statement from the International Marathon Medical Directors Association (IMMDA).
        Clin J Sport Med. 2006; 16: 283-292
        • CBC News
        Red Bull promotion near Halifax schools halted: energy drink maker tells province promotion was a mistake. Updated September 27, 2007.
        (Accessed September 3, 2010.)
        • Frishman WH
        • Del Vecchio A
        • Sanal S
        • Ismail A
        Cardiovascular manifestations of substance abuse: part 2: alcohol, amphetamines, heroin, cannabis, and caffeine.
        Heart Dis. 2003; 5: 253-271
        • Sudano I
        • Binggeli C
        • Spieker L
        • et al.
        Cardiovascular effects of coffee: is it a risk factor?.
        Prog Cardiovasc Nurs. 2005; 20: 65-69
        • Jones B
        Tapes reveal Stallworth had tequila, shots before fatal accident.
        USA Today. July 8, 2009; (Accessed September 3, 2010.)
        • Curry K
        • Stasio MJ
        The effects of energy drinks alone and with alcohol on neuropsychological functioning.
        Hum Psychopharmacol. 2009; 24: 473-481
        • Oteri A
        • Salvo F
        • Caputi AP
        • Calapai G
        Intake of energy drinks in association with alcoholic beverages in a cohort of students of the School of Medicine of the University of Messina.
        Alcohol Clin Exp Res. 2007; 31: 1677-1680
        • Wiklund U
        • Karlsson M
        • Ostrom M
        • Messner T
        Influence of energy drinks and alcohol on post-exercise heart rate recovery and heart rate variability.
        Clin Physiol Funct Imaging. 2009; 29: 74-80