Energy drinks boost blood pressure and may make the heart more susceptible to electrical short circuits, new research suggests.
But it's not clear how much of this effect on blood pressure has to do with caffeine, which also is found in coffee, or whether the effect significantly raises the risk of heart problems.
"I have no real concern that having an energy drink or two will negatively impact most people's health," said Dr. C. Michael White, a professor and head of pharmacy practice at the University of Connecticut. He has studied energy drinks and is familiar with the new review's findings.
However, he said, "there is enough information in this meta-analysis to make me concerned that there may be pockets of the population who may have an increased risk of adverse events, and more work needs to be done to see if this is true."
In other words, it's possible that some people could be especially vulnerable to the effects of energy drinks.
At issue are the caffeine-laden drinks that have become popular among people looking to stay alert, stay awake, or get a jolt. Sixteen-ounce cans of drinks like Monster Energy Assault and Rockstar pack in about 160 milligrams of caffeine, compared with roughly 100 milligrams in a 6-ounce cup of coffee.
Energy drinks also come with other ingredients like sugar and herbs, and medical experts have warned that they can spell trouble.
Industry representatives defend energy drinks, saying they contain about as much caffeine by the ounce as coffeehouse drinks. But people often consume much more of the energy drinks at one time.
In the new report, researchers looked at seven studies. Among them, a total of 93 participants drank energy drinks and had their "QT interval" measured, while another 132 underwent blood pressure measurement. In most of the studies, the participants -- aged 18 to 45 -- drank one to three cans of Red Bull.
The QT interval is an electrocardiogram (EKG) measurement of how the heart resets itself electronically while it beats. A longer interval raises the risk that a "short circuit" will develop in the heart and possibly kill a person.
The review found that the QT intervals lengthened after people consumed energy drinks. Federal officials would raise an alarm if a medication produced this level of an effect, said review co-author Dr. Ian Riddock, a preventive cardiologist at the David Grant Medical Center at Travis Air Force Base, in California.
One important question to answer, White said, is whether the effect on the heart goes up as people consume more of the drinks at a time or if it reaches a ceiling and stays there.
The review also found that the systolic blood pressure -- the top number in a blood pressure reading -- jumped by 3.5 points after participants consumed the drinks. That's not surprising considering the caffeine levels in the drinks, Riddock said. "But if this is going on [at] a chronic level, then it's worrisome," he said.
So what should consumers do? More research is needed, Riddock said, and "we need to start thinking about whether we need to regulate these things better."
The review findings were scheduled to be presented Thursday at an American Heart Association meeting in New Orleans. The report has not undergone the peer-review process that research must go through in order to be published in a scientific journal.