Department of psychiatry and
behaviral sciences; Duke University,
Meducal Center, Durham,
USA
CAFFEINE is one of the most popular drugs in
the world today, but its habitual use is not
without side effects. One of them is the clear
pattern of physiological withdrawal symptoms
that appears when habitual consumers abruptly
stop their intake. The best known symptom
following, sudden caffeine abstinence is
headache, which was described as early as 1952.
Studies in the late 1960s reported that abnormal
sleepiness and irritability were also common
symptoms. Withdrawal symptoms are not associated
only with high levels of chronic caffeine
intake. It was noted that withdrawal symptoms of
headache, fatigue, sleepiness and decreased
vigor, alertness and activity can occur even in
people who normally consume as little as 100 mg,
of caffeine per day. More severe symptoms have
been reported as well. For example, a study of
light to moderale coffee drinkers reported
increased scores for clinical symptoms of
depression and anxiety and the presence of
flu-like symptoms, in many individuals, after 2
days od caffeine abstinence.These symtoms of
caffeine withdrawal can clearly be clinically
signifian, and the may be quite common given the
widespread consumption of the drug.
Most experimental investigations of caffeine
withdrawal symptoms have involved several days
or more of caffeine deprivation. While extended
periods of deprivation provide the opportunity
to observe the full range and intensity of
clinical symptoms, extended deprivation is
relatively rare in everyday life. Much more
common are shorter periods of deprivation, for
example when someone misses his or her regular
morning coffee. Even such brief periods of
caffeine deprivation can lead to clinically
signifiant symptorns of headache and
fatigue.
A recent study in our laboratory
investigated mood, symptoms and psychomotor
performance in coffee drinkers who had drunk
coffee ad libitum or been abstinent during the
morning prior to testing at midday, an
experimental design intended to simulate these
natural episodes of brief deprivation. After
only a few hours of caffeine deprivation,
participants reported decreased energy, desire
to socialize and ability to concentrate as well
as increased drowsiness, lethargy and
yawning. Participants reported that they did
not feel like working, and headache and flu-like
feelings were reported by some. In contrast, we
detected no decrements in performance of a
variety of computerized psychomotor tasks.
The emphasis on natural conditions of
caffeinated beverage consumption in this study
raised two concerns about the interpretation of
results. First, participants differed in their
actual caffeine intake during the morning of ad
lib consumption, which could have made detection
of mood, symptoms and performance effects more
difficult by increasing the variability of
changes associated with acute deprivation.
Second, participants were aware of their
experimental condition on each day of testing.
Their expectations could have biased reports of
mood and symptoms, perhaps exaggerating the
differences between the ad lib and deprived
conditions.
The present study was designed to continue
the investigation of the effects of short-term
caffeine deprivation on mood, symptoms and
psychomotor performance under more controlled
conditions that would address the limitations of
the first study. The ad lib coffee consumption
and deprivation conditions were replaced by
double-blind administration of a fixed dose of
caffeine (250 mg) and placebo. Controlled doses
eliminated the variability in caffeine intake
associated with ad lib consumption. Double-blind
administration provided a control for
participants expectations and their influence on
symptoms and motivation for task performance.
These changes shifted the focus from the
naturalistic study of coffee drinking behavior
and isolated the contributions of the drug
caffeine to the pattern of mood, symptom and
performance effects observed after short-term
deprivation. [...]
DISCUSSION :
The results of this study confirm that some
withdrawal symptoms will appear in regular
coffee drinkers after only a few hours of
caffeine deprivation beyond normal overnight
abstinence. The pattern of affective and
sornatic symptoms sleepiness, yawning,
fatigue, decreased vigor are consistent with
previous studies, including our own. The results
of the present study demonstrate that the
effects can be attributed to caffeine and do not
require the presence and absence of the many
sensory and behavioral cues associated with
coffee drinking. Moreover, the doubleblind
counterbalanced administration of drug and
placebo treatments ensures that the effects
cannot be attributed to expectation,
experimental demand or other systematic
bias.
The failure to detect performance
degradation in the caffeine deprivation
condition contradicts the anecdotal reports of
participants, but is consistent with our earlier
study. The research literature suggests that
caffeine has inconsistent effects on cognitive
performance, especially when administered to
habitual consumers. Our experience suggests that
task length may be a critical variable in
studies of caffeine deprivation. Participants
appeared to be able to push themselves for the 2
Min of task performance required, and they may
have been able to overcome any deficits
associated with deprivation. Longer tasks may be
necessary to demonstrate the effects of caffeine
deprivation on performance. A recent study found
dramatic performance differences during
simulated managerial tasks conducted for 8-h
intervals. The authors attributed the success of
their demonstration to the complexity of the
tasks involved, but it is also possible that the
extreme length of the task revealed deficits
that could not be overcome by the temporary
efforts of caffeine deprived participants.
Future studies may be able to characterize the
nature of the psychomotor deficits that
participants report in their subjective
experience of caffeine deprivation.
This study found that acute caffeine
deprivation was associated with lower casual
blood pressure, confirming the results of an
earlier study. The difference of 5 mm Hg may be
important to understanding the relationship
between caffeine consumption and blood pressure
in the population. Epidemiological studies have
not consistently found elevated blood pressures
in coffée drinkers, as would be expected
given the experimental evidence of the pressor
effects of caffeine. However, many of the
epidemiological studies utilized blood pressure
measurements taken under conditions of acute
caffeine deprivation, which we showed in this
study are associated with a depressor response
in habitual consumers. The normal blood
pressures of coffee drinkers would be
underestimated when caffeine abstinence was
required, and the relationship between
coffée drinking and elevated blood
pressure may have been obscured in those
studies. Further consideration of the effects of
caffeine consumption on blood pressure in the
population is warranted given the popularity of
the drug and the importance of blood pressure as
a risk factor for cardiovascular disease, but
studies must take normal patterns of caffeine
consumption into account and avoid artifacts
related to acute caffeine deprivation.
The present study has two limitations that
may merit discussion. First, there was no
objective confirmation of compliance with the
caffeine treatment condition. Participants did
report following instructions for taking the
caffeine and placebo capsules according to
schedule, but caffeine concentrations in plasma
or saliva were not measured. Some participants
may have failed to comply with instructions for
abstinence from caffeinated beverages prior to
testing. However, random noncompliance would not
likely yield the observed pattern of significant
differences in mood and symptoms, nor would it
yield the lack of différences in
performance scores, which were caused more by
the consistency in the means across conditions
than by large variability in the participants'
scores. Thus, the lack of objective measures of
caffeine concentration is probably not a
important limitation of the present study.
Second, the estimated daily caffeine intake of
our sample of habitual coffee drinkers was
higher than might be expected. Mean caffeine
intake for our group was 603 mg/day, or 7.8
mg/kg of body weight, but recent estimates
suggest that caffeine-consuming adults average
only 4 mg/kg/day. This difference raises the
question of whether our results might apply only
to the heavier than average consumer, but we do
not think so. Our sample included participants
with a wide range of daily caffeine intakes, and
multiple regression analyses failed te, detect
any relationship between self-reported intake
and the magnitude of the changes associated with
caffeine deprivation. Apparently, cïffei'ne
deprivation had similar effects on moderate and
heavy consumers alike in our study, which should
at least partially resolve the issue of
generalizability to a broader range of caffeine
consumption.
Evidence of the measurable symptoms of
withdrawal associated with short-term caffeine
deprivation adds to our understanding of the
health consequences associated with habitual
consumption of caffeine in coffee, tea and other
products. To the extent that this research
paradigm mirrors normal patterns of consumption,
the results of this study demonstrate the kind
of effects that brief deprivation can have.
Because habitual coffee drinkers probably do
miss their morning coffée occasionally,
the associated pattern of sleepiness and fatigue
is a clear potential side effect of daily
consumption. Such mild symptoms may be merely an
annoyance for most people, but the increase in
sleepiness and fatigue could be critical in
occupations requiring sustained attention and
alertness, such as truck-driving and controlling
air traffic among others. Moreover, the aversive
symptoms of withdrawal following brief
deprivation may motivate continued daily morning
coffee drinking, a relationship that would
indicate the presence of physical dependence and
raise questions about caffeine as a potential
drug of abuse. Given the expanding popularity of
coffee and other caffeinated beverages in this
country, the harmful consequences of these side
effects merit further consideration.
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