Table 1.
Summary of studies that explored the effects of caffeine on cognitive function
| Author | Participants | Protocol | Outcome |
|---|---|---|---|
| Sleep Deprived | |||
| Hogervorst et al. 2008 [82] | Well-trained cyclists (n = 24) |
• Bar with 100 mg caffeine and 45.0 g CHO • Bar with only 45.0 g CHO • 300 mL non-caloric beverage |
*↑Stroop and Rapid Visual Information Processing tests after 140 min and time to exhaustion exercise trial at 75% VO2max |
| McLellan et al. 2007 [334] | Soldiers (n = 20) |
• 600 mg total caffeine in 200 mg does over 6 h period • Placebo |
*↑ Increased vigilance |
| McLellan et al. 2005 [329] | Soldiers (n = 31) |
• 200 mg caffeine (gum) mg doses over 5 h • Placebo |
Maintained vigilance in control observation and reconnaissance vigilance task |
| McLellan et al. 2005 [330] | Soldiers (n = 30) |
• 600 mg total caffeine in 100 mg and 200 mg doses over a 6 h period • Placebo |
Sustained marksmanship vigilance and accuracy *less decrease in urban operations vigilance |
| Lieberman et al. 2002 [42] | U.S. Navy SEAL trainees (n = 68) |
• 100 mg caffeine • 200 mg caffeine • 300 mg caffeine • Placebo |
*↑improved vigilance and reaction time in both the 200 and 300 mg caffeine interventions following 72 h sleep deprivation |
| Kamimori et al. 2015 [332] | Special Forces Operators (n = 20) |
• Four 200 mg doses of caffeine • Placebo |
*maintained psychomotor speed, improved event detection, increased the number of correct responses to stimuli, and increased response speed during logical reasoning tests. ⬌Live-fire marksmanship was not altered by caffeine. |
| Tikuisis et al. 2004 [335] | Young Military Subjects (n = 20) |
• 400 mg caffeine • 100 mg caffeine • 100 mg of caffeine • Placebo |
*increased cognitive component of shooting task |
| Not Sleep Deprived | |||
| Share et al. 2009 [336] | Elite male shooters (n = 7) |
• 2 mg/kg caffeine • 4 mg/kg caffeine • Placebo |
⬌ shooting accuracy, reaction time, or target tracking time between groups |
| Pomportes et al. 2019 [337] | Modern pentathlon national team athletes (n = 10) |
• Four counterbalanced sessions with: • 30 g CHO • 300 mg guarana complex • 200 mg caffeine • Placebo |
* enhanced speed of information processing w CHO, and caffeine and guarana complex * lower RPE w caffeine and gaurana complex |
| Duncan et al. 2019 [228, 338] | Younger males (n = 12) |
• 5 mg/kg dose caffeine • Placebo 60 min before 30 s upper body Wingate anaerobic test |
*Readiness to invest physical effort, and cognitive performance *Reduced rating of perceived exertion ⬌Response accuracy |
| Other Stressors | |||
| Share et al. 2009 [336] | Elite male shooters (n = 7) |
• 2 mg/kg caffeine • 4 mg/kg caffeine • Placebo |
⬌ shoot accuracy, reaction time, or target tracking time between groups |
| Gillingham et al. 2004 [339] | Military reservists (n = 12) | • 5 mg/kg caffeine or placebo dosed before 2.5 h loaded march plus 1 h sandbag wall construction task then re-dose of 2.5 mg/kg caffeine or placebo |
*↑ marksmanship performance (engagement time and number of shots fired) ⬌friend-foe discrimination |
| Zhang et al. 2014 [340] | Firefighters (n = 10) |
• 400 mg caffeine • Menthol lozenges • Placebo |
⬌ Change in perceived exertion, mood reaction time, short-term memory, or retrieval memory |
| Crowe et al. 2006 [341] | Healthy subjects: male (n = 12) female (n = 5) |
• 6 mg/kg caffeine • Placebo |
⬌ rating of perceived exertion |
| Foskett et al. 2009 [244] | Male soccer players (n = 12) |
• 6 mg/kg of caffeine • Placebo |
* Enhanced fine motor skills via improved ball passing accuracy and control |
| Stuart et al. 2005 [342] | Competitive male rugby (n = 9) |
• 6 mg/kg caffeine • Placebo |
*Increased ball-passing accuracy |
| Duvnjak-Zaknich et al. 2011 [343] | Moderately trained male athletes (n = 10) |
• 6 mg/kg caffeine • Placebo |
*Main effect for condition on decision time |
Outcomes are bold caffeine group specific; * = significant difference, ↑ = improved performance, ⬌ no change, mg/kg = milligram per kilogram, CHO = carbohydrate