Table 3:
Experimental Studies measuring the relationship between caffeine use and cognitive, behavioral and sleep measures
| First Author (Year) | Study Design | Study population | Goals | Measurement/Scales | Findings |
|---|---|---|---|---|---|
| Lieberman et al (2002) | A randomized placebo-controlled trial of caffeine. | Navy SEAL volunteers (N=68) randomly assigned to 100, 200, or 300 mg caffeine or placebo capsules | To examine whether moderate doses of caffeine reduce adverse effects of 72-hour sleep deprivation | *Neurocognitive battery to assess visual vigilance, reaction time, memory task, and self -reported fatigue and mood | * Higher doses of caffeine (200 or 300 mg doses) reduced sleepiness, fatigue, visual vigilance and reaction time. |
| Tharion et al (2003) | A randomized trial comparing caffeine, or placebo | Male Navy SEAL trainee volunteers (N=62) who used caffeine 100, 200, or 300 mg of caffeine or placebo | To evaluate the effect of caffeine at different doses to minimize performance deficits after sleep deprivation | *Marksmanship measures of sighting time, and accuracy | * When compared to placebo or 100 mg dose of caffeine, caffeine 200 and 300 mg improved their sighting time * Caffeine at any dose did not improve accuracy between these groups. |
| McLellan et al (2004) | A double-blind trial comparing caffeine and placebo | * Volunteer soldiers(N=16) * 400mg of caffeine at 21:30 followed by 2 doses of 100mg doses at 03:00 and 05:00. |
To investigate the effect of caffeine use on overnight military activity after a period of sleep loss | *Sandbag piling task * Time to exhaustion |
* Caffeine use reduced the time to complete the sandbag piling task in session 1 only, and not session 2 *Caffeine use improved the time to exhaustion by 25%, Vs placebo. |
| Tikuisis et al (2004) | A double-blind trial of caffeine and placebo | Volunteer soldiers (N=20), ingested 400, 300 and 100 mg of drug, 7.5, 3, or 0 hours before shooting | To appraise the efficacy of caffeine on improving performance after 22 hours of wakefulness | *Target engagement time *Number of shots fired *Accuracy *Precision |
*Caffeine restored the target engagement time, as compared to placebo; *Caffeine relatively improved the number of shots fired; * Caffeine did not improve any other measure. |
| McLellan et al (2005) (McLellan et al., 2005a) |
A randomized, placebo-controlled, double-blind trial of caffeine for performance during an urban warfare situation | Volunteer Soldiers (N=30), randomized to caffeine 600mg (N=15), or placebo (N=15). On night 1 they slept for 3 hours and stayed awake overnight in Night 2, till 11:00 on Day 3. Caffeine/placebo dose was given at 21:45 (100mg), 23:45 (200mg), 1:45 (100mg), and 3:45 (200mg). | To study the effect of caffeine on physical and cognitive performance during a 55-hour period of training operation that involved insufficient sleep | *PVT (Reaction time, major lapses) *5-km run *Marksmanship task *Urban Operation Vigilance Task |
*Reaction time was maintained with caffeine use on Day 3 * Minor lapses increased in the placebo group on Day 3 compared to the caffeine group that remained steady all through out *Marksmanship scores during sleep deprivation showed no marked change with caffeine use but decreased in the placebo group *Caffeine retained the Urban Operation Vigilance Task performance in the second session at 6:00, but not at 02:00. *5-km run did not show any between-group difference |
| McLellan et al (2005) (McLellan et al., 2005b) |
A randomized, placebo-controlled trial of caffeine | Special Forces Personnel (N=31), randomized to 200 mg of caffeine (N=16) or placebo (N=15). Day 1 had a 6.3-km run; on Day 2 they did an ORVT task in the field; on Day 3, after overnight sleep deprivation, ORVT done twice between 02:00 and 06:00. | To explore the effect of caffeine on vigilance, marksmanship, and run performance during 27 hours of sustained wakefulness | *PVT (Reaction time, major lapses) *Observation and Reconnaissance Vigilance Task (ORVT) *Marksmanship task |
*Caffeine use improved the Reaction Time on Day 3 starting 3:40 *Caffeine group had significantly fewer lapses * No difference in the run-time between groups, after sleep deprivation * No difference between groups on accuracy, target engagement time or response time scores (marksmanship) |
| Lohi et al (2007) | A double blind, placebo controlled trial of caffeine on flight performance in a simulator | Volunteer Finnish military pilot students on 200 mg of caffeine (N=7) or placebo (N=6) administered before 4 flight sessions (average of 24-33 minutes), performed between days 1-2 at 09:00-12:00, 18:30-21:30, 02:00-05:00, and 09:00-12:00. | To examine the effect of caffeine consumption on simulated flight performance during 37 hours of sleep deprivation | *Instructor score for overall flight performance on a scale from 1 to 5 *Instructor evaluation on a visual analog scale (VAS) *Self-evaluation of flight performance |
*The scores given by the instructor did not differ between either treatment group *No difference in self-reported scores recorded by the pilots in either group *After about 20 hours of sleep deprivation, a non-significant trend was seen for those treated with caffeine to rate their overall flight performance to be better than their first and second flight sessions. |
|
McLellan et al (2007) (McLellan et al., 2005b) |
A randomized study comparing caffeine to placebo | Male Special Forces Personnel given 200mg of caffeine (N=10) or placebo (N=10), between 0100, 0345, 0700, and 21:45. They slept for 4 hours on nights 3 and 4. | To investigate whether caffeine given during multiple nights of wakefulness could maintain physical functioning despite partial sleep deprivation | *Vigilance task *Obstacle tasks |
*Caffeine use improved vigilance scores, when compared to placebo, on days 3-5 *The total run time on caffeine during day 3 was faster on caffeine than on placebo. The run time decreased on days 4 and 5 for both groups. |
| Kilpelainen et al (2010) | A double-blind randomized trial of 200 mg caffeine or placebo | A sample of young Finnish male, military pilot students (n=15), randomized to 200 mg pf caffeine (N=7), or placebo (N=8), four times before each simulator session | Does a moderate caffeine dose prevent decrements in mood, motivation and task performance after 37-hour sleep deprivation | *Sustained Attention Task (Clock Test) * Learning Task (learning Japanese) * POMS (mood) * Motivation (VAS) |
*Sustained attention did not differ between the caffeine or placebo groups *No between-group difference in the Learning Task * Relative to placebo, caffeine prevented a deterioration of their mood symptoms |
| Newman et al (2013) | A double blind placebo-controlled cross-over study, involving 100 mg of caffeine or placebo. | Healthy, active-duty military personnel (N=15). Lights were switched off at 00:00, and woken at 01:00 to complete PVT, and then awakened again at 06:00 to do the PVT. | To explore the effect of caffeine during sleep inertia on PVT done at 0, 6, 12, and 18 min. post--awakening after sleeping for 1 and 6 hrs. | * speed of responses on PVT *number of lapses on PVT |
*At 1:00, the caffeine group maintained better speed increased at 12 and 18 min and lower lapses at 18 min. *At 6:00, the caffeine group showed improved speed at 18 min decreased lapses at 12 and 18 minutes |
| Kamimori et al (2015) | A randomized, double-blind, placebo-controlled trial of caffeine | Healthy male volunteers from special forces (N=20). Subjects were given placebo or caffeine 100 mg every 4 hours (total ≤800 mg). | To examine the efficacy of repeated 200mg caffeine doses on functioning after being awake for 3 nights and 4-h afternoon naps. | *PVT *Logical Reasoning test (LRT) *Field Vigilance Task (FVT) *Marksmanship test *Vigilance monitor (VM) |
*Caffeine use improved their: *reaction time (PVT), *improved event detection (FVT), *improved # of correct responses (VM), *speed of response (LRT). |
Legend: PVT = Psychomotor Vigilance Task, POMS = Profile of Mood States; VAS = Visual Analog Scale;