Is Caffeine Bad for Your Heart?
New Research Suggests Caffeine Elevates Blood Pressure, Stress
Aug. 1, 2002 -- Like millions of Americans, self-described coffee addict Kathy Liebswager can't quite function in the mornings until she has had her caffeine fix. She typically drinks eight to 10 cups throughout the day, and she says she believes the caffeine has a calming effect on her.
"When I worked, I literally couldn't think until I had had my first cup of coffee," the retired Navy counselor says. "There have been periods when I cut way down or mixed decaffeinated coffee with regular, but I definitely missed the caffeine."
Liebswager is not alone in thinking of caffeine as a stress reliever, but a new study suggests the opposite is true. Researchers at Duke University Medical Center found that caffeine actually exaggerates stress and its effect lasts throughout the day.
Even more troubling, the researchers concluded that the equivalent of four cups of coffee raises blood pressure for many hours. Although the increases appear modest, they are large enough to affect heart attack and stroke risk, says lead author James D. Lane, PhD. The findings were reported in the July/August issue of the journal Psychosomatic Medicine.
"The level of blood pressure change we saw has been associated with an increased risk of heart disease," Lane tells WebMD. "People consuming typical amounts of coffee and caffeinated soft drinks are probably raising their blood pressure by an amount equal to the beneficial reduction seen with antihypertensive drugs. So if you are taking blood pressure medication, it may not be doing you any good if you are drinking three or four cups of coffee a day."
Caffeine is consumed daily by an estimated 85% of adults in the U.S. in the form of coffee, tea, and sodas. The average daily number of cups per coffee drinker is 3.3, and 64% of all coffee is consumed at breakfast.
To determine the impact of caffeine consumption during the morning and early afternoon, Lane and colleagues recruited 47 daily coffee drinkers for a two-day study. Half of the subjects were given caffeine capsules on the first day and the other half were given placebo pills. On the second study day, the two groups were switched; the previous day's placebo group got the caffeine and the caffeine group got the placebo.
The total caffeine given equaled that found in four cups of coffee, and the capsules were consumed in the morning and at lunchtime. Blood pressure and heart rate were measured repeatedly on both days using a portable monitor, and stress hormone levels were monitored through urine samples.
When caffeine and placebo days were compared, the researchers found blood pressure to be consistently higher on the caffeine days -- an average of 4 millimeters (mm) higher for systolic pressure and 3 mm for diastolic. Stress hormone levels also rose by an average of 32% on the caffeine days, and both the blood pressure and adrenaline increase lasted throughout the day and into the evening.