Table 5.
Summary of studies examining the effects of caffeine and CHO in combination on cognitive performance and subjective mood.
| Author | Sample Size (Age) | Design (Within or Between Subjects) | Performance Measured (Relative to Drink Intake) | Drink (Volume/Vehicle) | Outcome Measures | Outcomes |
|---|---|---|---|---|---|---|
| Horne & Reyner, 2001 [179] | 11 (M = 24) | Within (restricted sleep (5 h); overnight caffeine fast) | 30 min drive–30 min break (drink)–2 h driving | (500 mL) caffeine 160 mg + 28.25 g CHO (11.3 g/100 mL) vs. placebo energy drink | Driving simulator (lane drifting and RT) | Caffeine + CHO significantly improved both lane drifting and RT. Effect strongest in 1st h |
| Warburton et al. 2001 [173] | Study 1: 20; Study 2: 22 (18–24) | Within (1 h caffeine abstinence) | +45 min | (250 mL) (Red Bull) 80 mg caffeine + 21 g sucrose + 5 g glucose +1 g taurine vs. Study 1: sugar-free water; Study 2: water + ~6 g glucose | RVIP; verbal reasoning; verbal and non-verbal memory test; Bond-Lader mood VAS | Energy drink improved attention, and verbal reasoning RT vs. glucose and non-glucose placebo, and reduced variability in RT performance. No difference between glucose and non-glucose drinks. No memory effects |
| Reyner & Horne, 2002 [182] | 12 (M = 24) | Within (overnight caffeine fast; restricted sleep (5 h)) | 30 min drive–30 min break (drink)–2 h driving | (250 mL) (Red Bull) 80 mg caffeine + 21 g sucrose + 5 g glucose vs. placebo version | Driving simulator (lane drifting and RT); EEG; Karolinska Sleepiness Scale | Caffeine + CHO = reduced sleep-related driving incidents and subjective sleepiness during the afternoon. Effect strongest in 1st 90 min |
| Kennedy & Scholey, 2004 [171] | Study 1: 30 (18–25); Study 2: 26 (18–24) | Double-blind, placebo-controlled, cross-over design (24 h; overnight fast and caffeine abstinence) | +10 min | Study 1: (380-mL) 38 mg caffeine + 68 g glucose vs. 46 mg caffeine + 68 g of glucose, vs. vehicle placebo; Study 2: (330-mL) 33 mg caffeine + 60 g glucose vs. just the vehicle. | 10 min cognitive test battery × 6 times (=60 min cog. demand): Serial 3s and 7s; RVIP; mental fatigue VAS | Both studies: improved accuracy of RVIP performance with all 3 active treatments. Effects emerged + 35 (38g and 46g caffeine) and +45 (33g caffeine) min after drink intake. 46 mg caffeine drink improve WM in initial 2 blocks. Higher dose of caffeine (46 mg) and caffeine drink (33 mg) reduced self-assessed mental fatigue during the extended period of cognitive performance (no effect of 38 g = baseline effect?) |
| Smit et al. 2004 [178] | Study 1: 28 (18–49); Study 3: 97 (18–55) | Study 1: Within (overnight caffeine abstinence); Study 3: Between (CHO (breakfast) deprived) | +5–+90 min | (250 mL) Study 1: 75 mg caffeine + 37.5 g glucose vs. placebo vs. water; Study 3: 62.5 mg caffeine + 37.5 g glucose vs. 62.5 mg caffeine vs. 62.5 mg caffeine + 37.5 g glucose non-carbonated | Simple RT; RVIP; immediate and delayed word recall; letter search task; mood VAS | Caffeine + glucose drinks improved and/or maintained mood (arousal) and RT performance during fatiguing and cognitively demanding tasks relative to placebo |
| Rao et al. 2005 [172] | 40 (18–30) | Between (no fasting; caffeine abstinence on test day) | Not known | (330 mL) 40 mg caffeine + 60 g glucose syrup vs. sweetness/flavor matched placebo | BP; HR; EEG; ERP; sustained selective attention | Glucose + caffeine drink = improved accuracy and RT on sustained selective-attention task vs. placebo. Glucose + caffeine = improved stimulus processing at several stages of information processing (ERP) |
| Anderson & Horne, 2006 [181] | 10 (=22.4) | Double blind, crossover design (1 week; restricted sleep (5 h); taken with soup lunch; ~14 h caffeine abstinence) | +10 min | (250 mL) 30 mg caffeine + 42 g sugars (glucose, fructose, sucrose) vs. sugar- caffeine-free orange flavored drink | Psychomotor Vigilance Test; Karolinska Sleepiness Scale | Energy drink did not counteract sleepiness and = slower RTs and more lapses 80 min post-intake |
| Smit et al. 2006 [184] | 76 (18–40) | Between (overnight food and caffeine fast) | +7–+120 min | (330 mL) Familiar drink: 30 mg caffeine + 54 g glucose vs. familiar drink placebo vs. Novel drink: 30 mg caffeine + 54 g glucose vs. novel drink placebo | Simple RT; RVIP; serial 7’s; letter search task; mood VAS | First exposure: familiar drink and its placebo improved alertness, mental energy and mental performance vs. baseline and novel placebo drink. Repeated exposure/increased familiarity with the novel drinks: both caffeine + CHO containing drinks = sustained beneficial effects vs. placebo drinks and baseline measures |
| Childs & de Wit, 2008 [177] | 35 (18–35) | Within (caffeine abstinence on test day) | Remained awake 5 p.m.–5 a.m. Energy capsule or placebo 3:30 a.m. Cog. testing +30 min | (Capsule) 200 mg caffeine + 50 mg white willow bark + 30 mg magnesium oxide + 10 mg taurine + 375 g dextrose vs. 375 g dextrose placebo | BP; physical activity meter; Simple and choice RT task; POMS and mood VAS | Caffeine = improved mood and mental energy and counteracted increases in simple and choice RT vs. placebo |
| Gendle et al. 2009 [175] | 36 (18–21) | Within (4 h fast and caffeine abstinence) | +30 min | (250 mL) 80 mg caffeine + 1000 mg taurine + 27 g glucose/sucrose vs. sugar and caffeine free version | Visual attention and RT (Conner’s Continuous Performance Test II) | No effects |
| Howard & Marczinski, 2010 [176] | 80 (M = 20.1) | Between (2 h fast; 8 h caffeine abstinence) | +30 min | Energy drink doses calculated by body weight. Caffeine content for average 78 kg ppt given in (): 1.8 mL/kg energy drink (45.6 mg) vs. 3.6 mL/kg energy drink (91.2 mg/30.8 g CHO) vs. 5.4 mL/kg energy drink (136.7 mg) vs. 3.6 mL/kg placebo drink (29.3 g CHO) vs. no drink) | Cued go/no-go task; mental fatigue VAS | Energy drink = increased stimulation, decreased mental fatigue, and decrease behavioral control RT. No effect on response inhibition. Lowest caffeine dose = greater RT and subjective measure improvement. Improvements diminished as the dose increased |
| Mets et al. 2011 [183] | 24 (M = 21–35) | Within | Drive 2 h–drink intake–drive 2h | (250 mL) (Red Bull) 80 mg caffeine + 21 g sucrose + 5 g glucose + 1 g taurine + vs. placebo (Red bull) drink | STISIM Drive™ driving simulator (standard deviation of lateral position (SDLP); standard deviation of speed); subjective driving quality and mental effort; Karolinska Sleepiness Scale | Energy drink significantly improved driving relative to placebo: SDLP reduced in 3rd and 4th h. Reduced standard deviation of speed, improved subjective driving quality, and reduced mental effort during 3rd hr. Subjective sleepiness was significantly decreased in 3rd and 4th h of driving |
| Aniţei et al. 2011 [174] | 153 (18–21) | Between | +40 min | 275 mg caffeine coffee vs. energy drink (1000 mg taurine + 80 mg caffeine + sucrose/glucose (not stated) vs. 275 mg caffeine + energy drink vs. no drink | Perceptual speed; visual and auditory attention RT; visual orientation performance; vigilance test | Caffeine alone and combined with CHO in energy drink increased motor reactivity, short-term attention (under 30 min) and visual attention RT. Effects less consistent/smaller when caffeine and energy drink combined (365 mg caffeine) |
| Sünram-Lea et al. 2012 [185] | 81 (M = 26) | Between (overnight fast + standardized breakfast; caffeine abstinence from waking) | +10 (pre-stressor) and +60 min (post-stressor) | (330-mL) 40 mg caffeine + 50 g glucose vs. 80 mg caffeine + 10.25 g fructose (41%)/glucose (59%) vs. placebo drink | Salivary cortisol; CBG; immediate and delayed free word call; letter cancellation task; grammatical reasoning task; letter digit substitution task; hand grip strength | 50 g glucose +40 mg caffeine =increased grip strength and improved memory performance. Both active drinks = improved information processing (letter-digit substitution task) performance vs. placebo. 50 g glucose/40 mg caffeine = reduced anxiety and subjective stress. No effects on reasoning and attention or subjective alertness |
| Scholey et al. 2014 [180] | 150 (18–55) | Between (12 h fast and caffeine abstinence) | +30 min | (330 mL) 40 mg caffeine + 60 g glucose vs. 25 g glucose vs. 60 g glucose | CBG; salivary caffeine level; multi-tasking framework (4 simultaneous tasks: mathematical processing task; stroop; memory search; target tracker task); Bond–Lader mood VAS; stress and fatigue VAS | Co-administration of glucose and caffeine = greater multi-tasking performance than placebo or glucose alone |
CHO—carbohydrate; EEG—electroencephalogram; VAS—visual analogue scale; RVIP—Rapid Visual Information Processing. EEG—electroencephalogram; VAS—visual analogue scale; RVIP—Rapid Visual Information Processing; ERP—event-related potential; BP—blood pressure; HR—heart rate; POMS—Profile of Mood States. CHO – carbohydrate; VAS—visual analogue scale; SDLP—standard deviation of lateral position. VAS—visual analogue scale; CBG—capillary blood glucose.