Nov. 6 (HealthDay News) -- Energy drinks boost blood pressure and heart rate and could pose risks to people with hypertension and heart disease, say Wayne State University researchers.

They found that drinking two cans of a popular energy drink increased blood pressure and heart rate in 15 healthy adults, average age 26.

Within a few hours of having the energy drinks, the volunteers' systolic blood pressure (top number) increased by as much as 9.6 percent, and diastolic blood pressure increased by as much as 7.8 percent. Heart rate increased by as much as 11 percent.

"This occurred while participants were sitting in chairs watching movies," study leader James Kalus noted in a prepared statement. "The increase in heart rate and blood pressure weren't enough for something to happen acutely, but a person on hypertension medication or who has a cardiovascular disease may not respond as well."

"While energy drinks increase concentration and wakefulness, people with risk factors for heart disease could have a bad reaction. The subjects in this study were healthy with low blood pressure," Kalus added.

He and his colleagues noted that most energy drinks contain high levels of caffeine and an amino acid called taurine, both of which have been shown to have effects on heart function and blood pressure. The researchers emphasized that energy drinks are different from sports drinks, which don't contain ingredients designed to heighten alertness.

The study was expected to be presented Nov. 6 at the American Heart Association annual meeting, in Orlando, Fla.

SOURCE: Nov. 6, 2007, presentation , American Heart Association annual meeting, Orlando, Fla.