The effects of brief caffeine deprivation on
vigilance performance, mood, and symptoms of
caffeine withdrawal were studied in habitual
coffee drinkers. Thirty male and female coffee
drinkers were tested twice at midday (1130 to
1330 hours) after mornings in which they either
consumed caffeinated beverages ad lib or
abstained. Vigilance performance was tested with
a 30-min computerized visual monitoring task.
Mood and withdrawal symptom reports were
collected by questionnaires. Caffeine
deprivation was associated with impaired
vigilance performance characterized by a
reduction in the percentage of targets detected
and an increase in response time, and by
subjective reports of decreased vigor and
increased fatigue and symptoms characterized by
sleepiness, headache, and reduced ability to
work. Even short periods of caffeine
deprivation, equivalent in length to skipping
regular morning coffee, can produce deficits in
sustained attention and noticeable unpleasant
caffeine-withdrawal symptoms in habitual coffee
drinkers. Such symptoms may be a common
side-effect of habitual caffeine consumption
that contributes to the maintenance of this
behavior.
CAFFEINE is one of the most popular drugs in
the world today, and it is consumed by more than
85% of Americans. Unfortunately, the habitual
use of caffeine is not free of detrimental
consequences for health and well-being. Perhaps
the most common adverse effect of habitual
caffeine consumption is the pattern of symptoms
that characteristically appears when habitual
consumers abruptly stop caffeine intake, a
syndrome labeled caffeine withdrawal. The
clearest symptom of caffeine withdrawal is
headache, which was described in the literature
as early as 1952. The caffeine withdrawal
syndrome is also characterized by sleepiness and
fatigue, irritability, and difficulty
concentrating, and some studies have reported
the appearance of flu-like symptoms and
clinically meaningful levels of depression and
anxiety. Caffeine withdrawal is a concern not
only for heavy coffee drinkers. Symptoms of
headache, fatigue, sleepiness and decreased
vigor, alertness, and activity were observed on
days of abstinence in people who normally
consumed as little as 100 mg of caffeine per
day, which is the amount contained in a single
cup of coffee. Given the experimental evidence
and the widespread consumption of caffeine in
coffee, tea, soft drinks and medications, the
majority of the population is at risk for the
appearance of the caffeine withdrawal syndrome
if their normal patterns of intake are
disrupted. The impact that this syndrome may
have on health and behavior deserves
investigation.
Most experimental investigations of caffeine
withdrawal symptoms have involved several days
or more of caffeine deprivation, a research
strategy that provides the opportunity to
observe the full range and intensity of clinical
symptoms. However, such extended periods of
abstinence are rare in everyday life. We have
recently been investigating the effects of
shorter periods of deprivation, equivalent to
the situation in which someone misses his or her
morning coffee. Such periods of deprivation,
lasting only a few hours beyond the time of
normal consumption, are probably common in the
course of daily life. Evidence from our studies
and those of other investigators suggests even
brief deprivation can lead to noticeable
symptoms of headache and fatigue in habitual
coffee drinkers.
In our studies, habitual coffee drinkers
have been examined at midday following mornings
of caffeine intake or caffeine deprivation.
Studies have contrasted both ad lib consumption
versus voluntary abstinence and fixed doses of
250 mg of caffeine versus placebo administered
in capsules under double-blind conditions. When
deprived of caffeine for only a few hours,
habitual coffee drinkers reported decreased
energy, desire to socialize, ability to
concentrate, and urge to work, as well as
increased drowsiness, lethargy, and
yawning. Headache and flu-like feelings
were reported by many. Despite the subjective
symptoms that appeared, deprivation had no
effect on psychomotor performance measured with
a battery of brief (2 mm) tasks that assessed a
range of simple and complex cognitive functions
including motor speed, reaction time, working
memory, and logical reasoning. The short
duration of these tasks may have contributed to
the failure to detect impaired psychomotor
performance, because participants reported
casually that they could push themselves to
overcome the deficits they felt. The present
study was conducted to characterize further the
effects of brief caffeine deprivation and to
explore whether psychomotor deficits might be
apparent in a longer task. After mornings of ad
lib caffeine consumption or voluntary caffeine
abstinence, habitual coffee drinkers rated their
mood and experience of withdrawal symptoms and
performed a 30-min visual monitoring vigilance
task. The vigilance task was selected because
caffeine is often used to enhance or sustain
attention during monotonous circumstances. Given
the symptoms associated with caffeine withdrawal
in our studies, we hypothesized that sustained
attention and vigilance performance would suffer
when coffee drinkers were deprived of
caffeine.
DISCUSSION
These results confirm our earlier studies
and suggest that even brief periods of caffeine
deprivation, lasting only a few hours beyond the
time that caffeine would normally be consumed in
the morning, can produce significant changes in
mood and symptoms associated with caffeine
withdrawal. Moreover, this brief deprivation was
associated with a deficit in the performance of
a visual monitoring vigilance task, reducing the
number of targets detected and slowing the speed
of response.
The effects on mood and symptom reports
replicate closely our earlier findings for
caffeine deprivation of this duration, in
studies that compared ad lib and abstinent
conditions and double-blind administration of a
fixed moderate dose and placebo. These effects
can be summarized as representing subjective
feelings of decreased alertness and increased
sleepiness along with increased irritability and
decreased interest in work and in socializing.
Headache does appear in some, but not all,
individuals with this length of deprivation.
Such symptoms could have a negative impact on
performance of daily activities and would
definitely be considered aversive.
The demonstration of a significant
impairment of vigilance performance in this
study contrasts with our earlier failure to
detect performance effects with a battery of
brief psychomotor tasks. At the present time we
cannot determine whether either the duration or
the nature of the task made a difference.
Certainly it was less likely that deprived
participants could overcome the subjective
effects of caffeine withdrawal for the 30 min
required by the vigilance task, as they had
reported doing when tasks lasted 2 min or less.
The significant interaction of caffeine
condition and trial block, which showed that the
decrement grew over time, supports the argument
that task duration contributed to the detection
of a deprivation effect. The deprivation-related
performance decrement was ambiguous in the first
5 min of the task, but was clearly present later
on. Moreover, performance demonstrated a greater
negative slope and a larger positive quadratic
component after deprivation. However, the
characteristics of the vigilance task, which
required sustained attention and effort under
monotonous conditions without immediate feedback
on performance, may also have contributed to the
demonstration of a decrement in performance.
Certainly tasks of this nature represent many
kinds of common everyday work activity. The
results of this laboratory study may perhaps be
generalized to similar tasks in the natural
environment, for which performance may also
suffer when habitual coffee drinkers are
deprived of caffeine.
The comparison of ad lib intake and
abstinence conditions was designed to simulate
natural circumstances of caffeine consumption
and deprivation, although this approach has two
potential limitations. Ad lib intake did vary
among the participants, which could have
obscured treatment effects by increasing
variability in dependent measures. However,
treatment effects were observed despite
variability in intake, and
correlation/regression analysis found that the
variations in intake could not consistently
account for variations in the effects. Second,
given the nature of the experimental treatments,
participants were not blind to the experimental
conditions of testing. As a result, expectations
about the effects of caffeine intake or
abstinence may have contributed to the treatment
differences. However, such expectations would be
present under the natural conditions of
consumption and deprivation where the effects of
caffeine deprivation would be important.
Moreover, we have previously reported similar
mood and symptom effects of caffeine deprivation
when treatments were administered double-blind
and expectations were controlled. Thus, the
presence of expectations is probably not an
important limitation for the interpretation of
these results.
These results have two implications for
understanding caffeine consumption in the real
world. First, brief periods of caffeine
deprivation in habitual caffeine consumers may
have a meaningful impact on everyday mood and
work performance. Although occasional episodes
of caffeine deprivation might not be detrimental
to overall work performance in many occupational
situations, some work activities do demand
constant vigilance. Air-traffic control and
interstate highway trucking can be offered as
two examples of occupations that cannot afford
even intermittent bouts of sleepiness and
impaired attention. Here caffeine deprivation
effects might prove to be more critical, and
field studies might be appropriate to determine
how caffeine deprivation affects performance and
safety in these and other similar occupations.
Second, the aversive nature of the mood,
symptom, and performance changes associated with
caffeine withdrawal may have implications for
understanding the motivations that maintain
habitual caffeine consumption. When caffeine is
consumed daily, overnight abstinence will lead
to the systemic clearance of caffeine from the
body and the presence of withdrawal symptoms
apparent upon awakening. Relief of these
aversive symptoms would provide reinforcement
for caffeine consumption in the morning, which
might contribute significantly to the
maintenance of typical daily caffeine
consumption behaviors. More research is needed
to clarify the relative contributions of
negative and positive reinforcement in caffeine
consumption, which will speak to the issue of
whether caffeine is a drug that creates physical
and psychological dependence.
Caffeine consumption is nearly ubiquitous,
and the effects of caffeine consumption
influence the lives of the vast majority of the
population. The investigation of brief caffeine
deprivation provides insight into one aspect of
caffeine consumption behavior that may have
implications for public health and safety.
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