Your morning cup of coffee may be doing more harm than previously thought, according to a new study by Medical Center researchers that shows caffeine consumed in the morning increases blood pressure and amplifies stress throughout the day.
The study, published in the July/August 2002 issue of Psychosomatic Medicine, is the first to demonstrate caffeine's lasting stress effects in a clinical setting.
"When regular coffee drinkers ingest caffeine, they are raising their blood pressure and adrenaline levels above what they would be without caffeine," said James Lane, associate research professor of behavioral psychiatry and lead author of the study. He added that even if a person does not consume any caffeine after 1 p.m., the effects may persist until bedtime.
To investigate caffeine's effects, the researchers recruited 47 habitual coffee drinkers, mostly Duke employees.
The researchers measured their response to caffeine on two separate days. On one day, the coffee drinkers were given a 250-milligram dose of caffeine in the morning and again at lunchtime, equivalent to four cups of coffee in total. On the other day, they were given placebos in an identical capsule and at the same times. Neither the coffee drinkers nor the researchers knew when the placebos were being administered, and several days were allowed in between for regular coffee consumption.
The coffee drinkers were each hooked up to a portable monitor that measured blood pressure and heart rate four times an hour, from morning until bedtime. In addition, the participants were asked to collect urine samples to measure the levels of stress hormones like cortisol and adrenaline, and to record their feelings of stress every time their blood pressure was measured.
"What we found is that the average blood pressure was elevated on the caffeine days," said Lane, who has studied the health effects of caffeine for the past 15 years. "These effects were present both during the workday and at nighttime... and this is without any caffeine after lunchtime."
The researchers also found that the coffee drinkers felt more stressed, their adrenaline levels were over 30 percent higher and their heart rate increased on the caffeine days.
"Caffeine is eliminated by the liver, but it takes three to five hours for the liver to get rid of half of it, and it takes another three to five hours to get rid of the next quarter, and so on," Lane explained. "So lunchtime coffee may affect sleep."
Lane warned that although moderate coffee drinking does not represent a severe health risk, a lifetime of extensive caffeine consumption may pose health problems. "It is well established that stress is linked to higher risk of heart disease, stroke and death," Lane said. "Stress is bad for you."
Caffeine consumption may especially endanger those with existing stress conditions and diseases exacerbated by stress, such as the type II form of diabetes, Lane noted. "People who already have high stress and use caffeine might want to eliminate it. Our data suggests they may feel less stressed without it," he said.
"Think about the effect coffee is having in your life," Lane advised.
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Several coffee drinkers said the findings are a motivation to consume caffeine in moderation.
"People drink too much caffeine, but they need it to get through their day," said Katherine Haggerty, a Perkins Library assistant who also works at a local coffee shop. "It perks you up, makes you feel better." Haggerty, who said she drinks coffee and tea regularly, warned against drinking too much caffeine to avoid getting jittery.
Added senior Katie Van Wert, "[Coffee] may be stressful, but no more than a stressful career--or m Mom." She said she has started drinking decaffeinated coffee to ease her addiction.