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Rationale: Various occupational groups are required to maintain optimal physical and cognitive function during overnight periods of wakefulness, often with less than optimal sleep. Strategies are required to help mitigate the impairments in cognitive function to help sustain workplace safety and productivity., Objectives: To test the effectiveness of repeated 200 mg doses of caffeine on cognitive function and live-fire marksmanship with soldiers during three successive nights of sustained wakefulness followed by 4-h afternoon sleep periods., Methods: Twenty Special Forces personnel (28.6 ± 4.7 years, 177.6 ± 7.5 cm and 81.2 ± 8.0 kg) were randomly assigned to receive four 200-mg doses of caffeine (n = 10) or placebo (n = 10) during the late evening and early morning hours during three successive days. An afternoon 4-h sleep period followed. The psychomotor (PVT) and field (FVT) vigilance, logical reasoning (LRT) tests and a vigilance monitor assessed cognitive function throughout the study. Live-fire marksmanship requiring friend-foe discrimination was assessed., Results: Caffeine maintained speed on the PVT (p < 0.02), improved detection of events during FVT (p < 0.001), increased number of correct responses to stimuli as assessed by the vigilance monitor (p < 0.001) and increased response speed during the LRT (p < 0.001) throughout the three overnight testing periods. Live-fire marksmanship was not altered by caffeine., Conclusions: A total daily dose of 800 mg caffeine during successive overnight periods of wakefulness is an effective strategy to maintain cognitive function when optimal sleep periods during the day are not available.

Energy drinks (EDs) contain caffeine and are a new, popular category of beverage. It has been suggested that EDs enhance physical and cognitive performance; however, it is unclear whether the claimed benefits are attributable to components other than caffeine. A typical 235 mL ED provides between 40 and 250 mg of caffeine, equating to doses that improve cognitive and, at the higher levels, physical performance. EDs often contain taurine, guaraná, ginseng, glucuronolactone, B-vitamins, and other compounds. A literature search using PubMed, Psych Info, and Google Scholar identified 32 articles that examined the effects of ED ingredients alone and/or in combination with caffeine on physical or cognitive performance. A systematic evaluation of the evidence-based findings in these articles was then conducted. With the exception of some weak evidence for glucose and guaraná extract, there is an overwhelming lack of evidence to substantiate claims that components of EDs, other than caffeine, contribute to the enhancement of physical or cognitive performance. Additional well-designed, randomized, placebo-controlled studies replicated across laboratories are needed in order to assess claims made for these products., (© 2012 International Life Sciences Institute.)

The effects of caffeine-induced arousal on global versus local object focus were investigated in non-habitual consumers using a double-blind, within-subjects, repeated-measures design. Following an overnight fast, low caffeine consumers (N=36; M=42.5mg/day caffeine) completed 5 counterbalanced test sessions (normal consumption, 0mg, 100mg, 200mg, and 400mg) separated by at least 3 days. During each session, volunteers either consumed their normal amount of caffeine or were administered 1 of 4 treatment pills. One hour later they completed two tasks assessing visual attention, in counterbalanced order. Measures of mood, salivary caffeine and cortisol were taken at multiple time points. Dose-dependent elevation of caffeine in the saliva demonstrated the experimental manipulation was effective. Furthermore, analyses of the mood and arousal measures detected consistent changes on arousal subscales and caffeine administration elevated saliva cortisol. Analyses of the visual attention tasks revealed that caffeine-induced physiological arousal produced global processing biases, after as little as 100mg caffeine. These data suggest caffeine consumption may influence how individuals attend to and process information in their environment and could influence daily tasks such as face recognition, learning new environments and navigation, especially for those who normally consume little caffeine., (Published by Elsevier Inc.)

Recent work suggests that a dose of 200-400 mg caffeine can enhance both vigilance and the executive control of visual attention in individuals with low caffeine consumption profiles. The present study seeks to determine whether individuals with relatively high caffeine consumption profiles would show similar advantages. To this end, we examined the effects of four caffeine doses (0 mg, 100 mg, 200 mg, 400 mg) on low- and high-level visual attention in individuals with high consumption profiles (n=36), in a double-blind study using a repeated measures design. Results from the Attention Network Test indicated that caffeine enhanced both vigilance and the executive control of visual attention, but only at the highest administered dose (400 mg). We demonstrate that in habitual consumers high doses of caffeine can produce beneficial changes in visual attention. These results carry implications for the theorized interactions between caffeine, adenosine and dopamine in brain regions mediating visual attention., (Published by Elsevier Inc.)

The cognitive dimension of mental energy can be assessed by tests of vigilance and choice reaction time. These behaviors are relatively simple cognitive functions and can be measured with precision and reliability if carefully designed and implemented tests are used. Because the concept of mental energy is still evolving, the selection of appropriate tests to assess it must be tentative. However, vigilance and choice reaction time seem to have the necessary psychometric properties for assessing mental energy, including construct, predictive content, and face validity. Tests of reaction time and vigilance are correlated with questionnaires that measure mood states corresponding to mental energy--such as sleepiness, fatigue, and alertness--in the expected manner and are of approximately equivalent sensitivity.

The serotonin system may contribute to reduced human performance when hypohydrated in the heat. This study determined whether branched-chain amino acid (BCAA) supplementation could sustain exercise and cognitive performance in the heat (40 degrees C dry bulb, 20% relative humidity) when hypohydrated by 4% of body mass. Seven heat-acclimated men completed two experimental trials, each consisting of one preparation and one test day. On day 1, a low-carbohydrate diet was eaten and subjects performed exhaustive cycling (morning) and treadmill exercise in the heat (afternoon) to lower muscle glycogen and achieve the desired hypohydration level. On day 2, subjects consumed an isocaloric BCAA and carbohydrate (BC) or carbohydrate-only drink during exercise. Experimental trials included 60 min of cycle ergometry (50% peak oxygen uptake) followed by a 30-min time trial in the heat. A cognitive test battery was completed before and after exercise, and blood samples were taken. BC produced a 2.5-fold increase (P < 0.05) in plasma BCAA and lowered (P < 0.05) the ratios of total tryptophan to BCAA and large neutral amino acid. Blood prolactin, glucose, lactate, and osmolality were not different between trials but increased over time. Cardiovascular and thermoregulatory data were also similar between trials. BC did not alter time-trial performance, cognitive performance, mood, perceived exertion, or perceived thermal comfort. We conclude that BCAA does not alter exercise or cognitive performance in the heat when subjects are hypohydrated.

Purpose: Navy SEALs (sea, air, land) are elite special warfare units that conduct unconventional warfare primarily in marine environments. Marksmanship accuracy and sighting time were quantified with 62 male trainees during Navy SEAL Hell Week, which involves the combined stress of sleep loss, operational combat scenarios, and cold-wet environmental conditions. Caffeine was administered to minimize deficits due to sleep deprivation., Methods: Volunteers dry-fired a disabled rifle equipped with a laser-based marksmanship simulator system to measure shooting speed and accuracy. The target was a 2.3-cm diameter circle at a distance of 5 m, simulating a 46 cm target at a distance of 50 m. Marksmanship was assessed prior to training, and at 73 and 80 h into Hell Week. Volunteers were randomly assigned to 1 of 4 treatments: 100, 200, or 300 mg of caffeine or a placebo. Dosing occurred 72 h after training commenced., Results: The combined effects of almost 73 h of total sleep deprivation and operational and environmental stress degraded all marksmanship accuracy measures (p < 0.05) as shown by the 37.5% increase in percent of targets missed, 38% increase in distance from center of mass of the target, and the 235% increase in shot group tightness. Sighting time increased by 53% or 3.1 s after 73 h of sleep deprivation (p < 0.05). Sighting time was significantly faster in sleep deprived individuals after taking 200 or 300 mg of caffeine compared with placebo or 100 mg of caffeine. No differences in accuracy measures between caffeine treatment groups were evident at any test period., Conclusion: During periods of sleep deprivation combined with other stressors, the use of 200 or 300 mg of caffeine enabled SEAL trainees to sight the target and pull the trigger faster without compromising shooting accuracy.

Purpose: We wanted to determine whether sleep is disrupted when soldiers sleep in a new chemical protective mask, the M40. Sleep quantity and quality, extent of protection provided by the mask during sleep, and next day performance were assessed., Method: After several days of training, 9 male soldiers slept with and without the M40 mask on four occasions., Results: Soldiers were able to tolerate the mask for most or all of the night. However, sleep, as assessed by wrist-worn activity monitors, was significantly disturbed. Minutes (mean +/- SEM) of waking significantly increased, from 25 +/- 2.1 to 86 +/- 8.5 per night (p < 0.001), and number of awakenings rose from 8 +/- 0.6 to 20 +/- 0.9 (p < 0.0001). Soldiers reported that it took longer and was more difficult to fall asleep when wearing the mask. Errors on a choice reaction time task increased significantly and subjects reported greater fatigue and sleepiness the day after sleeping in the mask. Protection provided by the masks varied substantially among subjects and declined over the course of the study. Some soldiers were protected throughout the night but others were only protected intermittently., Conclusion: We conclude that sleeping in the chemical protective mask should only be done when necessary, given the adverse effects on sleep and daytime function, as well as the variability of protection, of the mask.

Melatonin (10, 20, 40, or 80 mg, PO) or placebo was administered at 1145 hours on five separate occasions to 20 healthy male volunteers and the effects on serum melatonin levels, mood, performance, and oral temperature were monitored. Subjects were studied between 0930 and 1700 hours. A battery of interactive computer tasks designed to assess performance and mood was completed, oral temperature was measured, and blood samples were taken for serum melatonin radioimmunoassay. The areas under the time-melatonin concentration curve (AUC) varied significantly in proportion to the various melatonin doses. Compared with placebo treatment, all melatonin doses significantly decreased oral temperature, number of correct responses in auditory vigilance, response latency in reaction time, and self-reported vigor. Melatonin also increased self-reported fatigue, confusion, and sleepiness.

In humans, exposure to bright light at night suppresses the normal nocturnal elevation in circulating melatonin. Oral administration of pharmacological doses of melatonin during the day, when melatonin levels are normally minimal, induces fatigue. To examine the relationship between illumination, human pineal function, and behavior, we monitored the overnight serum melatonin profiles and behavioral performance of 24 healthy male subjects. On each of three separate occasions subjects participated in 13.5 h (1630-0800 h) testing sessions. Each subject was assigned to an individually illuminated workstation that was maintained throughout the night at an illumination level of approximately 300, 1500, or 3000 lux. Melatonin levels were significantly diminished by light treatment, F(2, 36) = 12.77, p < 0.001, in a dose-dependent manner. Performance on vigilance, reaction time, and other tasks deteriorated throughout the night, consistent with known circadian variations in these parameters, but independent of ambient light intensity and circulating melatonin levels.

Caffeine, in addition to being a food constituent, is also a common analgesic adjuvant that is used in combination with aspirin in certain over-the-counter preparations. Caffeine has previously been shown to significantly improve certain aspects of human performance, particularly sustained vigilance, when administered in low and moderate doses (32 to 256 mg). We therefore attempted to determine whether caffeine, in the dose (64 mg) found in some over-the-counter drugs, retains this beneficial property when combined with aspirin. We also measured self-reported mood state, using various standardized questionnaires, since caffeine has been reported to have both beneficial and adverse effects on alertness and anxiety. We observed that caffeine (64 mg), when added to aspirin (800 mg), significantly improves vigilance performance and increases self-reported efficiency when compared with either placebo or aspirin alone. As previously reported, this caffeine dose alone significantly increased vigilance and decreased reaction time. No adverse effects of caffeine were detected on any of the parameters that were assessed. This study therefore demonstrated that the addition of caffeine to aspirin, in a dose commonly employed in over-the-counter drugs, has significant beneficial consequences with respect to mood and performance.

Caffeine is thought to have stimulant-like behavioral effects on mood and performance. However few behavioral studies have examined this substance's acute effects when administered in a range of doses that include the low doses typically found in foods and over-the-counter drugs. We therefore gave single doses of caffeine (32, 64, 128 and 256 mg) to 20 healthy male subjects and assessed various aspects of performance and self-reported mood states, as well as plasma caffeine concentration. As little as 32 mg (which elevated plasma caffeine concentration to less than 1 microgram/ml), typical of the dose found in a single serving of a cola beverage, and less than that found in a single cup of coffee or a single dose of over-the-counter drugs, significantly improved auditory vigilance and visual reaction time. All other caffeine doses administered also significantly improved performance on these tests. No adverse behavioral effects, such as increased anxiety or impaired motor performance, were noted even at the highest dose administered.

We examined the behavioral effects of the dietary constituents tryptophan and tyrosine on human mood, sensorimotor performance and pain sensitivity. Tryptophan and tyrosine are neurotransmitter precursors present in varying amount in protein-containing foods. Tryptophan (50 mg/kg) increased subjective drowsiness and fatigue but unlike many hypnotics did not impair sensorimotor performance. Tryptophan also decreased human pain sensitivity in a manner that was more specific than certain analgesic drugs.