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.