By Alison McCook

NEW YORK (Reuters Health) Jul 30 - People who consume caffeine may experience an increase in blood pressure, feel more stressed and produce more stress hormones than on days when they opt for decaf, US researchers report.

Furthermore, Dr. James D. Lane and his colleagues at Duke University in Durham, North Carolina found that the effects of caffeine appear to persist until people go to bed, even if they do not consume any caffeine after 1 pm.

Given the long-lasting effects of caffeine, the authors suggest that regular consumption of the substance could contribute to the risk of heart disease. Furthermore, Dr. Lane told Reuters Health that any condition influenced by stress could also be aggravated by caffeine.

For example, in people with type 2 diabetes stress can worsen the condition by influencing glucose metabolism, Dr. Lane said. He added that people with stress-related conditions, such as post-traumatic stress disorder or social anxiety, could also experience adverse effects from caffeine consumption.

"Any stress-related disease could be aggravated by caffeine," Dr. Lane said.

In the current study, 47 regular coffee drinkers consumed 500 milligrams of caffeine in the form of two pills, the rough equivalent of the amount of caffeine contained in four 8-ounce cups of coffee. The second pill was taken no later than 1 pm. Each participant took caffeine pills or placebo on alternate workdays, and frequently recorded their levels of stress. The participants did not know if the pills contained caffeine or placebo.

The researchers monitored the participants' blood pressure and heart rate, and performed urinalyses.

Reporting in the July/August issue of Psychosomatic Medicine, Dr. Lane's group found that the subjects had slightly higher blood pressure levels, produced 32% more of the stress hormone epinephrine, and felt more stressed on the days they took the caffeine pill compared with the days they took placebo.

In an interview with Reuters Health, Dr. Lane said that the effects of caffeine likely persist because it has an average half-life of 4 hours.

Dr. Lane added that he hesitates to tell people exactly how much caffeine they should consume each day. However, for those with conditions that are aggravated by stress, or have high blood pressure, "one simple thing they can try is to cut back on caffeine," he said, and see if that helps alleviate their symptoms.

Cutting out caffeine "doesn't cost a thing, and it may make you feel better. So it's worth a try," Dr. Lane advised.

Psychosom Med 2002;64:593-603.

Caffeine Affects Cardiovascular and Neuroendocrine Activation at Work and Home


OBJECTIVE: This study investigated the effects of moderate doses of caffeine on ambulatory blood pressure and heart rate, urinary excretion of epinephrine, norepinephrine, and cortisol, and subjective measures of stress during normal activities at work and at home in the evening.

METHODS: Healthy, nonsmoking, habitual coffee drinkers (N = 47) participated in 3 days of ambulatory study. After a day of ad lib caffeine consumption, caffeine (500 mg) and placebo were administered double-blind in counter-balanced order on separate workdays. Ambulatory blood pressure and heart rate were monitored from the start of the workday until bedtime. Urinary excretion of catecholamines and cortisol was assessed during the workday and evening.

RESULTS: Caffeine administration significantly raised average ambulatory blood pressure during the workday and evening by 4/3 mm Hg and reduced average heart rate by 2 bpm. Caffeine also increased by 32% the levels of free epinephrine excreted during the workday and the evening. In addition, caffeine amplified the increases in blood pressure and heart rate associated with higher levels of self-reported stress during the activities of the day. Effects were undiminished through the evening until bedtime.

CONCLUSIONS: Caffeine has significant hemodynamic and humoral effects in habitual coffee drinkers that persist for many hours during the activities of everyday life. Furthermore, caffeine may exaggerate sympathetic adrenal-medullary responses to the stressful events of normal daily life. Repeated daily blood pressure elevations and increases in stress reactivity caused by caffeine consumption could contribute to an increased risk of coronary heart disease in the adult population.

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James D. Lane, PhD, Carl F. Pieper, DrPH, Barbara G. Phillips-Bute, PhD, John E. Bryant, PhD and Cynthia M. Kuhn, PhD
From the Department of Psychiatry and Behavioral Sciences (J.D.L., B.G.P.-B., J.E.B.), Department of Community and Family Medicine and The Center for the Study of Aging and Human Development (C.F.P.), and Department of Pharmacology (C.M.K.), Duke University Medical Center, Durham, NC.

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Key Words: caffeine • ambulatory monitoring • blood pressure • catecholamines • cortisol • occupational stress


Abbreviations: DASH = Dietary Approaches to Stop Hypertension; • DBP = diastolic blood pressure; • HR = heart rate; • SBP = systolic blood pressure.

Do you know if Caffeine acts differently in a low carb person that a low fat person? I noticed coffee acts different to me. I drink 12oz cup of coffee a day. I noticed since low carbing I don't stay awake like I did before... then again its hard to judge isn't it?