Effects of Caffeine
Differ in Men and Women

Researchers have long known that caffeine increases blood pressure. Now, new findings show that this blood pressure rise may occur for different reasons in men and women.

The investigators found that, in women, caffeine tends to raise blood pressure by increasing the activity of the heart, causing it to pump blood faster and raising so-called cardiac output. In contrast, caffeine ups men's blood pressure by narrowing blood vessels, increasing the resistance of blood vessels to the flow of blood.

Although caffeine appears to raise pressure for different reasons in men and women, blood pressure increased by the same amount in both sexes, suggesting that the potential health risks of caffeine are the same for men and women, study author Dr. William R. Lovallo stated.

"Caffeine can increase blood pressure, and it can elevate pressure still further when a person is under mental stress," he said. "If you are developing high blood pressure, or if you already have high blood pressure, give up caffeine."

During the study, Lovallo and his colleagues asked premenopausal 42 women and 35 men of similar ages to take either an inactive pill or a pill containing as much caffeine as 2 to 3 cups' worth of coffee. All participants were in good health, had normal blood pressure and drank coffee regularly.

To induce mental stress, the researchers then asked some of the people who took caffeine to make a speech in front of a video camera and two researchers wearing white coats.

The investigators found that caffeine raised blood pressure by the same amount in men and women. However, men responded to the caffeine pills by showing an increase in blood vessel resistance, with no change in cardiac output. In contrast, women showed no change in vessel resistance, and instead showed an increase in cardiac output, according to the American Journal of Cardiology report.

Lovallo, who is based at the Veterans Affairs Medical Center and the University of Oklahoma Health Sciences Center in Oklahoma City, explained that previous research has established that caffeine tends to increase blood pressure in men by increasing constriction of blood vessels.

Although the reasons why women showed a different response are not clear, researchers have shown that public speaking may provoke more anxiety in women than in men, he noted.

"When women are experiencing anxiety, they may have greater increases in how forcefully their hearts contract, in comparison to men. As a result, caffeine may have intensified the anxiety and response of the heart in the women, creating the difference in responses we saw," Lovallo said.

SOURCE: American Journal of Cardiology, April 15, 2004.

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