SAN DIEGO -- People who drink four or five cups of coffee throughout the morning have slightly elevated blood pressure and higher levels of stress hormones all day and into the evening, creating a scenario in which the body acts like it is continually under stress, according to a group of Duke University Medical Center scientists.
In a study of 72 habitual coffee drinkers, the researchers found that subjects produced more adrenaline and noradrenalin and had higher blood pressure on days when they drank caffeine compared with days they abstained. The two stress hormones are vital to helping the body react quickly in times of danger or stress, but they can damage the heart over a lifetime of heightened production, said James Lane, associate research professor of psychiatry at Duke.
Lane prepared results of his study, funded by the National Heart, Lung and Blood Institute, for presentation Thursday to a meeting of the 1999 Society of Behavioral Medicine.
"Moderate caffeine consumption makes a person react like he or she is having a very stressful day," Lane said in an interview before the meeting. "If you combine the effects of real stress with the artificial boost in stress hormones that comes from caffeine, then you have compounded the effects considerably."
During the two-week study, the subjects experienced, on average, a 32 percent increase in adrenalin and a 14 percent increase in noradrenaline on days when they consumed caffeine. Their blood pressure rose an average of 3 points.
Lane's study builds on smaller ones in which he found that caffeine boosted blood pressure, heart rate and stress hormones in subjects who drank 4 to 5 cups of caffeine per day. In the current study, Lane replicated those findings and added to them by showing that subjects' blood pressures and stress hormone levels stayed elevated until bedtime, even though they last consumed caffeine between noon and 1 p.m.