Page 81 - Journal of Special Operations Medicine - Winter 2016

powdered drinks (http://hprc-online.org/comrad). In fact, other brain functions. However, the amount of caffeine
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consumption of approximately 200–300mg of caffeine is ingested, metabolic characteristics, and genetics ulti-
encouraged to maintain vigilance and delay sleep onset mately determine the magnitude of subsequent actions
during continuous operations. This recommendation is of caffeine on brain responses. Like many drugs, caf-
3
15
based on extensive research examining caffeine’s effect feine may operate in the brain and body based on an
on performance in rested and sleep-deprived individu- inverted U-shaped function. Figure 1 presents such an
als (discussed later). Although most Special Operations idealized curve showing the desired effects come from
Forces (SOF) consume caffeine in coffee, many Ser- moderate doses or levels of caffeine, whereas negative
vicemembers also report consuming energy drinks and effects are elicited at higher doses. Consumption of low
energy shots. More than 80% of Servicemembers use to moderate doses of caffeine may produce desired ef-
4
caffeine daily. Even though the prevalence of use in the fects, but high amounts can be hazardous. For example,
5
military is similar to that of civilians, the average amount Chelben and colleagues reported clinical cases where
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consumed is much greater. 1,5,6 Servicemembers who are the overuse of energy drinks containing a combination
regular caffeine users report consuming greater than of amino acids and caffeine may have led to hospital-
300mg/day, whereas the average amount consumed by ization for hypervigilance, psychomotor unease, and ag-
5
civilians is closer to 180–240mg/day. 1,6 gravated mental state. Associations also have been made
between caffeine consumption and the onset of mania.
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Psychiatric classifications of caffeine-related disorders
Drug Properties
include caffeine intoxication, caffeine withdrawal, other
Although caffeine is a naturally occurring substance in a caffeine-induced disorders, and unspecified caffeine-
variety of plants, it is also a drug that, when introduced related disorder. These disorders are diagnosed based
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into the body, exerts physiological and psychological ef- on symptoms that occur after consuming caffeine (typi-
fects. Caffeine has its most marked effects in the brain, cally in doses in excess of 250mg) or after prolonged
7
where low and moderate doses are associated with in- use. Abrupt cessation can cause significant distress or
creased alertness and deferred fatigue. Importantly, in- impairment to the user, which clearly demonstrates that
8
terindividual differences in the metabolism, clearance, caffeine should be used carefully and in an intentional
and elimination of caffeine and its metabolites vary manner for performance-enhancing effects. Unit medi-
widely. For example, peak levels of caffeine in the blood cal personnel should be aware of signs and symptoms of
after ingestion are usually reached within 15 minutes caffeine overdose as well as withdrawal and be prepared
but may take up to 120 minutes. The half-life of caf- to act when necessary to abate those negative effects.
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feine in healthy adults is approximately 4–5 hours. 10 Further, by knowing the caffeine content of medications
(e.g., Excedrin ) and other substances regularly used,
®
Some factors that influence the metabolic and excretion medical personnel can educate unit members about these
rates of caffeine include smoking, dietary intake, rate products and the role caffeine plays in performance.
of gastric emptying, and genetics. Interestingly, the me-
tabolism of caffeine by smokers is almost twice as fast Figure 1 The inverted U-shaped curve as it may relate to
as that by nonsmokers, and habitual or heavy users of caffeine and performance. As the dose of caffeine goes up
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(>200mg), the beneficial effects are reversed and negative
caffeine metabolize caffeine faster than do nonusers. Im- adverse effects may become apparent. Lower doses do not
portantly, consuming more than 6mg/kg caffeine (420mg negatively affect performance; however, no clear benefit
for a 70kg [154lb] person or 600mg for a 100kg [220lb] is expected. Depending on body weight, mission, caffeine
person) appears to saturate hepatic caffeine metabolism. 7 metabolism, and typical caffeine use, the best dose is between
100mg and 200mg every 3 or so hours.
One of caffeine’s well-known actions is blocking adenos-
ine receptors. Adenosine is an endogenous substance
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involved in many bodily processes, including energy
transfer, slowing heart rate, modulation of neurotrans-
mission, and blood flow, to name a few. Additionally,
the buildup of adenosine across the day leads to a need
for sleep. Thus, caffeine and adenosine have opposing
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actions. Genetic differences in adenosine receptor sensi-
tivity and numbers may alter caffeine’s effects, particu-
larly with regard to alertness. 14,15

Caffeine also indirectly increases dopamine, norepi-
nephrine, and serotonin, which are brain chemicals or
neurotransmitters associated with mood, reward, and

Caffeine and Performance 65