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OCR for page 143
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
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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
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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.
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Representative terms from entire chapter:
blood pressure
