DURHAM, N.C. -- A study by researchers at Duke University
Medical Center shows that caffeine taken in the morning has
effects on the body that persist until bedtime and amplifies
stress consistently throughout the day. These results show for
the first time that the effects of caffeine last considerably
longer than originally thought, said the scientists, and that
caffeine exaggerates stress in people who consume it every
day.

The study, which was funded by the National Institutes of Health, appears
in the July/August 2002 issue of Psychosomatic
Medicine.

"The effects of coffee drinking are long-lasting and
exaggerate the stress response both in terms of the body's
physiological response in blood pressure elevations and stress
hormone levels, but it also magnifies a person's perception of
stress," said James D. Lane, Ph.D., associate research
professor in the department of psychiatry and behavioral
sciences at Duke and lead author of the study. "People haven't
really accepted the fact that there could be a health downside
to caffeine consumption, but our evidence – and that of other
studies – shows that this downside exists and people should be
aware of it in order to make the best possible health
choices."

To determine the effects of caffeine on people as they go
about their normal activities, the researchers enrolled 47
healthy, habitual coffee drinkers in a double blind,
placebo-controlled study. That is, neither the participants nor
the researchers knew when the participants were receiving
caffeine or the placebo.

To qualify for the study, the coffee drinkers were asked to
fill out a daily diary of caffeine intake for a period of one
week. They kept the diary in order to determine the average
amount of caffeine they consumed on a daily basis, the type of
caffeinated beverages they drank, and the variation from day to
day, all of which helped verify the participants as habitual
coffee drinkers.

Once the coffee drinkers qualified for the study, their
responses to caffeine were measured on two different, randomly
chosen days. On one day, the coffee drinkers were given a
250-milligram dose of caffeine in the morning and again at
lunchtime. On the other day, they were given identical capsules
containing a placebo at the same time interval. The doses of
caffeine -- equal to four cups of coffee -- and the dosage
times were chosen to reflect normal patterns of coffee drinking
in adults. Half of the study participants received caffeine on
the first day of study and the others received it on the second
day. The coffee drinkers were given, on average, two to three
days off between study days during which they could consume as
many caffeinated beverages as they normally desired.

On both study days, coffee drinkers wore a portable monitor
that measured blood pressure and heart rate four times an hour
from early morning until bedtime, while they went about their
normal daily activities. They were asked to collect urine
samples so that the researchers could measure the amount of
stress hormones they had produced that day. They were also
asked to keep a diary to record their perceived stress levels
as well as their physical position – standing, sitting or lying
down – each time the monitor was activated.

When the researchers compared the caffeine days to the
placebo days they discovered that caffeine consumption
significantly raised systolic and diastolic blood pressure
consistently throughout the day and night, and adrenaline
levels rose by 32 percent. The researchers found that the
elevated levels persisted as the evening progressed to
bedtime.

The study also showed that while caffeine increases blood
pressure and heart rate, it also amplifies those effects at the
times when participants report higher levels of stress during
their day, said Lane. The caffeine appears to compound the
effects of stress both psychologically in terms of perceived
stress levels and physiologically in terms of elevated blood
pressures and stress hormone levels -- as if the stressor is
actually of greater magnitude, he said.

"The caffeine we drink enhances the effects of the stresses
we experience, so if we have a stressful job, drinking coffee
makes our body respond more to the ordinary stresses we
experience," he said. "The combination of stress and caffeine
has a multiplying, or synergistically negative effect.

"Everyone accepts that stress can be unhealthy. Our results
suggest that drinking coffee or other caffeinated drinks can
make stress even more unhealthy."

The researchers noted that while habitual coffee drinkers
might be expected to demonstrate tolerance to the effects of
caffeine, they still showed significant responses to the
drug.

"Our findings indicate that eliminating coffee and other
caffeinated beverages from the diet could be a helpful way to
decrease blood pressure and other stress reactions," said Lane.
"I think that people who feel 'stressed out' should at least
consider quitting caffeine to see if they feel better. Quitting
caffeine could be particularly beneficial for people suffering
from high blood pressure, just as diet and exercise can help
keep blood pressure under control."

The researchers said that despite the perceived safety of
overwhelmingly popular caffeinated beverages such as coffee,
the drug does show short-term negative health effects that, if
continued over a period of years, could increase risk of heart
attack and stroke.

"While today's cup of coffee might not, by itself, cause you
much harm, the cumulative effects of drinking it day after day
over a lifetime could really be unhealthy," Lane concluded.

Other authors on the study are Carl Pieper, DrPH, Barbara
Phillips-Bute, Ph.D., John Bryant, Ph.D., and Cynthia Kuhn,
Ph.D., all of Duke.