If you have high blood pressure, you might want to avoid downing energy drinks, like Red Bull, according to a new study conducted by Wayne State University researchers.

The researchers found drinking two cans a day of a popular energy drink increased blood pressure and heart rate in 15 healthy adults with an average age of 26.

"While the increases didn’t reach dangerous levels in the healthy volunteers, the increases in blood pressure and heart rate could prove to be clinically significant in patients with heart disease or in those who consume energy drinks often," said study leader James Kalus, senior manager of Patient Care Services at Henry Ford Hospital in Detroit, Mich., and a former Wayne State researcher, in a news release.

Within four hours of consuming the energy drinks, the participants maximum systolic blood pressure (top number) shot up by as much as 9.6 percent, and diastolic blood pressure (the bottom number) increased by as much as 7.8 percent. Heart rate also went up by as much 11 percent.

“This occurred while participants were sitting in chairs watching movies,” said Kalus. “The increases in heart rate and blood pressure weren’t enough for something to happen acutely, but a person on hypertension medication or who has cardiovascular disease may not respond as well.”

Energy drinks generally contain high levels of caffeine and taurine, an amino acid also found in protein-containing foods such as meats and fish. Both have had effects on heart function and blood pressure in some studies. In contrast, “sports drinks” often contain various mixtures of water, sugars and salts alone, without chemicals aimed at increasing “energy” or alertness, the researchers offered as background.

“While energy drinks increase concentration and wakefulness, people with risk factors for heart disease could have a bad reaction," said Kalus.

Until further research is done, Kalus said people with high blood pressure or heart disease should avoid energy drinks because they could affect their blood pressure and may even alter the effectiveness of their medications.

The study was presented at the American Heart Association’s Scientific Sessions 2007 in Orlando, Fla., which wraps up today.