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Cortisol and Caffeine

Guest Bernadette

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Guest Bernadette

(8/30/00 HeartInfo) - Drinking two to three cups of coffee can elevate blood pressure and increase the body's production of a stress hormone known as cortisol, studies have shown. This is true whether you drink coffee while relaxed or under stress, even if you drink caffeinated beverages regularly. Caffeine may also reduce the effectiveness of hypertension medications, research suggests.

Graduate student Jack D. Shepard and colleagues from the University of Oklahoma Health Sciences Center in Oklahoma City studied the effects of caffeine on medical students. The team reports their findings in the May 3 American Journal of Hypertension. Few studies have examined the effects of stress and caffeine on people outside of the laboratory setting, the team notes.

Drinking caffeinated beverages while under stress from taking exams caused systolic blood pressure to rise to above 140 mm Hg. The increase in blood pressure with stress and caffeine is more than if the person wasn't ingesting caffeine, the authors write.

The combined effect on blood pressure is so great that people who are likely to develop hypertension should avoid caffeinated beverages, particularly when they are under stress, the team reports. In addition, people who are going to have their blood pressure taken should avoid caffeine.

The study participants were 31 healthy, male, coffee-drinking medical students. Of these, 20 were at low risk of developing hypertension, based on family history, and because their blood pressure was less than 125/78 mm Hg. The others had a family history of high blood pressure, and their blood pressures were between 125/78 mm Hg and 139/89 mm Hg.

During the randomized, double-blind, crossover trial, researchers measured the students' blood pressure and cortisol levels before two low-stress lectures and two stressful exams. Prior to the lectures and exams, the students drank either six ounces of unsweetened grapefruit juice laced with the amount of caffeine found in two cups of coffee (3.3 -mg/kg) or grapefruit juice alone.

Blood pressure increased by 4/1 mm Hg in the low risk group and by 7/3 mm Hg in the high-risk group in response to stress alone, and by 5/4 mm Hg versus 3/3 mm Hg in response to caffeine alone. Consuming caffeine during the high-stress times produced a double whammy --- blood pressure in the low risk group increased by 9/5 mm Hg and by 10/6 in high-risk group. The differences between the two groups were not statistically different.

However, during the exams when dranking caffeine, men in the high-risk group experienced a blood pressure jump to the hypertensive range. Their elevated blood pressure remained high for at least 4 hours.

Cortisol levels were increased by the stress of exams and by consuming caffeine. The combination of caffeine and stress increased cortisol levels by 7.4 nmol/L, an increase much greater than from stress alone.

Is it okay for such individuals to indulge in caffeine on occasion while under stress? "There are no [national] guidelines for caffeine intake currently," coauthor Dr. William R. Lovallo told HeartInfo. But these results "indicate it would be best to avoid it....The magnitude of the blood pressure effect that we saw is big enough to significantly reduce the effect of medication or other beneficial lifestyle changes," he warned.

The Oklahoma researchers have recently found women have a similar response to caffeine as men while under stress, but the mechanisms causing their blood pressure increase appears to differ, Dr. Lovallo told HeartInfo.


---Shepard, J. D., et al., "Additive Pressor Effects of Caffeine and Stress in Male Medical Students at Risk for Hypertension," American Journal of Hypertension, Volume 13, May 2000, pgs. 475 -448.

---Chamberlain Communications Group, Inc. press release, May 2000.  

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