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B Previous Recornrnendations on Caffeine from the Committee on Military Nutrition Research The following is an excerpt from: Institute of Medicine. 1994. Food Com- pontents to Enhance Performance. Washington, DC: National Academy Press. Pp.32-34, 5~57. CAFFEINE The literature on the effects of caffeine on behavior, performance, and health is extensive and somewhat contradictory (for reviews see, for example, Bergman and Dews, 1987; Graham 1987; Hughes et al., 1988; Jarvis, 1993; Smith et al., 1994a,b). David Penetar and colleagues (chapter 20) present a new study on the effects of caffeine on cognitive performance, mood, and alertness in human subjects who had been sleep-deprived, and summarize current knowl- edge about the use of such supplements. Caffeine is known to exert its central nervous system-mediated effects by blockade of adenosine receptors. Its stimu- lant effects when compared with those of other drugs such as amphetamines are weak, but most studies to date suggest that it tends to delay sleep, reduce the deterioration of performance associated with fatigue and boredom, and decrease steadiness of the hands, particularly when performance is already partially de- graded by repetitive, nonintellectual tasks. Less well understood are the effects of caffeine in reversing changes caused by sleep deprivation. To clarify these issues, three doses of caffeine (150, 300, and 600 mg/70 kg of body weight) were assessed among normal healthy males after 2 days of sleep deprivation. Cognitive performance, mood, alertness, vital signs, serum caffeine concentrations, and plasma catecholamine levels were also assessed. Cognitive performance was measured using a computerized assessment battery. Choice reaction time (for 8 hours) significantly improved after caffeine administration, although tests of code substitution and immediate and delayed recall were unaffected. 143
144 CAFFEINE FOR MENTAL TASK PERFORMANCE Mood was assessed by ratings on a profile of mood states questionnaire. Sig- nificant increases in vigor were reported for 2 hours after taking the dose, with decreases in fatigue and confusion. Also, significant improvements in mood for 2 hours postdose were reported on visual analog scales for increased alertness, confidence, energy level, and talkativeness and decreased sleepiness. However, anxiety and jitteryness/nervousness also increased. At 12 hours postadministra- tion, ratings for increased energy levels, decreased sleepiness, and jittery- ness/nervousness remained elevated. Alertness, assessed by the modified multiple sleep latency test, also im- proved for 4.5 hours after caffeine administration, returning to 50 percent of rested levels when the highest doses were used. Oral body temperature remained elevated for 12 hours and blood pressure (diastolic) for one hour, but neither rate nor systolic blood pressure were elevated. It was concluded that large doses of caffeine reversed sleep deprivation- induced degradation in cognitive performance, mood, and alertness without serious side effects. These data were consistent with those represented in most other studies reviewed. Therefore, Penetar et al. (Chapter 20) recommended that caffeine be included in rations at 250 mg per tablet and that it be made available to soldiers for maintaining performance during specific military operations. The authors did not study individuals with habitually high levels of caffeine inges- tion; it would be useful to determine whether the effects of the doses of 30~600 mg noted in this study were as pronounced in individuals with markedly higher levels of typical intakes. Sustaining optimal soldier performance is recognized to depend on other measures as well. The first is training, so that tasks can be performed with a minimal level of cognitive effort, cross-training so that individuals can substitute for each other, developing and adhering to appropriate work and rest cycles, exercising wise leadership so that unnecessary demands are not placed on sub- ordinates, and modification of systems to minimize errors. Second is enforcing sleep discipline so that the sleep-deprived individual sleeps as much as he or she can and in as hygienic a manner as possible. The relationship between caffeine intake and health outcomes, particularly cancer incidence, cardiovascular disease (CVD), and effects on fertility, and pregnancy and child outcome, has been the focus of many studies. While data from individual studies have been contradictory, reviews tend to conclude that there is no significant association or negligible/transient effects relating moder- ate caffeine consumption and cancer, CVD, fertility, and osteoporosis (see, for example, AMAC, 1984; Cooper et al., 1992; Gordis, 1990; Joesoef et al., 1990; Johansson et al., 1992; Lubin and Ron, 1990; Olsen, 1991; Rosenberg, 1990; Schairer et al., 1986; Wilson et al., 1989~. However, reports continue to demon- strate that caffeine intake causes an elevation in blood pressure (Smith et al., 1994a,b). Although the blood pressure elevation produced by caffeine has been interpreted as transient and within the range produced by typical activities
APPENDIXB 145 (HHS, 1988; Myers, 1988), blood pressure bears monitoring in any future stud- ies of performance enhancement with caffeine supplementation. Recent reports that assess the safety of caffeine consumption during pregnancy have continued to produce conflicting information (Eskenazi, 1993; Infante-Rivard et al., 1993; Mills et al., 1993~. These data indicate that high levels of caffeine intake (> 300 mg/d) potentially increase the risk of spontaneous abortion and intrauterine growth retardation during pregnancy (Mills et al;, 1993~. The risk to pregnant women of low levels of caffeine intake is uncertain. Further, women often do not realize they are pregnant and/or do not receive prenatal care until after the time period when most spontaneous abortions occur. Should the Army pursue further research in performance enhancement using caffeine products, these health issues must be carefully considered. In summary, continued research on the mechanisms for the evident effects of caffeine on cognitive performance, mood, and alertness and how these may be enhanced in combination with other dietary measures is warranted. Of par- ticular interest is how to maximize positive effects when performance is already degraded. Individual differences, expectancy, and placebo effects need further elucidation. In the meantime, practical applications of demonstrated effects in ration planning may be in order. COMMITTEE RECOMMENDATIONS REGARDING FOOD COMPONENTS PROPOSED BY THE ARMY 1. The following components have clearly demonstrated their ability to enhance performance under appropriate simulated conditions and should be evaluated in appropriate delivery systems. Caffeine. Caffeine functions as a weak stimulant that, in low doses, tends to delay sleep and reduce the deterioration of performance associated with fatigue and boredom At higher doses caffeine reverses the sleep deprivation-induced degradation in cognitive performance, mood, and alertness. The long experience with the use of coffee suggests that caffeine is safe at levels required to achieve the desired effects, and its effects are reversible over time. The primary issues that need to be answered in providing caffeine are the appropriate carrier that should be used to provide the supplement and the amount required to achieve the desired benefit in those both habituated and nonhabituated to it. Since it would not be desirable to inhibit sleep when operations permit, the timing of in- gestion and availability of the caffeine-containing food component should be evaluated.