Nov. 6, 2007 (Orlando, Fla.) -- Energy drinks may boost your blood pressure and heart rate as well as your vitality, researchers say.
In a small study, they found that drinking just two cans of a popular drink increased blood pressure and heart rate within four hours.
While the increases didn't reach dangerous levels in the healthy volunteers studied, they could be harmful for people with heart disease or who are taking medication to control blood pressure, says James Kalus, PharmD, senior manager of patient care services at Henry Ford Hospital in Detroit.
"These people should avoid these drinks," he tells WebMD.
"Pending more study, at least talk to your doctor about potential risks," Kalus says.
The findings were presented at the American Heart Association's (AHA) Scientific Sessions 2007.
Energy Drinks Raise Blood Pressure
In the study, 15 healthy young men and women drank two cans of an energy drink that contained 80 milligrams of caffeine every day for a week. All agreed to abstain from any other forms of caffeine for two days prior to and throughout the study.
Within four hours of consuming the drinks on the first day, systolic blood pressure (the top number) shot up by 9 points; on the seventh day, it rose 10 points. Diastolic blood pressure (the bottom number) rose 5 points on both days, Kalus says.
Heart rate increased five beats per minute on the first day; seven days on the last.
The volunteers were sitting in a chair, watching a movie, when the changes occurred, he says.
In contrast, many young people mix the energy drinks with alcohol and dancing. And some of the marketing for energy drinks is aimed at extreme sports, he says.
Since it wasn't studied, Kalus says he can't say for certain that mixing energy drinks with booze or exercise raises the risks. But some countries advise against using energy drinks to quench thirst while playing sports, according to the AHA.
And just yesterday, researchers reported that college students who mix alcohol with energy drinks are at higher risk for alcohol-related injuries than students who drink cocktails alone.
Energy Drinks Pack Caffeine Punch
AHA President Daniel Jones, MD, of the University of Mississippi Medical Center in Jackson, tells WebMD that he always cautions his patients to watch their caffeine intake.
"Energy drinks are a new source of caffeine -- and one of which many people aren't aware," he says.
Some energy drinks contain even higher amounts of caffeine than the product studied. A recent review of a dozen popular drinks in Consumer Reports found caffeine levels, which often aren't listed on the label, can top 200 milligrams per bottle or can.
While the energy drink used in the study had as much caffeine as one to two cups of coffee, Kalus says that "comparing the two is like comparing apples and oranges. Each contains other compounds that could have good or bad effects on the heart."
Energy drinks contain taurine, an amino acid found in protein-rich foods like meat and fish that generally has been found to have positive effects on the heart, he says. And coffee has phenol, an antioxidant that has been shown to reduce the risk of heart disease, he says.