New Orleans, Louisiana — Tossing back one to three energy drinks may result in more than just a buzz. A small-meta analysis found that immediately afterward, subjects had increased systolic blood pressure and, more troubling, they also had, on average, a 10-msec prolongation in their QT interval [1].

The study, by Dr Sachin Shah (University of the Pacific, Stockton, CA) and colleagues, was presented at EPI-NPAM 2013, the Epidemiology and Prevention/Nutrition, Physical Activity and Metabolism 2013 Scientific Sessions.

"The blood-pressure finding falls in line with what we would suspect because of the caffeine content," Shah told heartwire . "The QT prolongation that we are seeing--I was very surprised with that. It's a bit of a wake-up call for us investigators to start studying it a bit more thoroughly, and it needs to happen sooner rather than later."

The group aimed to see how energy drinks affect heart health, given that these drinks, along with dietary supplements, are not regulated as stringently as new drugs that must meet Food and Drug Administration (FDA) safety requirements, Shah said.

In a literature search, they identified seven observational and interventional trials that evaluated the impact of energy drinks on QT interval, blood pressure, and heart rate.

Three studies with a pooled sample of 93 subjects had QT/QTc data. Six studies with a pooled sample of 132 subjects had blood-pressure data, and seven studies investigated heart rate.

The patients, who were all young (aged 18 to 45) and healthy, underwent ECG and blood-pressure testing before and just after drinking one to three cans of energy drink--most commonly Red Bull, but also others such as Full Throttle and Meltdown RTD. An 8.4-oz can of Red Bull contains 80 mg of caffeine, compared with 35 mg of caffeine in a 12-oz Coke or about 100 mg of caffeine in an average cup of coffee, Shah said.

Shortly after drinking the energy drinks, the pooled subjects had a systolic blood pressure increase of an average 3.5 mm Hg. "If people are drinking energy drinks every day, that change in blood pressure could be very significant," Shah noted, adding that, as reported by heartwire , research on torcetrapib was terminated because of a similar 3-mm-Hg increase in blood pressure.

People who don't normally drink coffee might have a heightened blood-pressure response to an energy drink, he added.

In a clinical setting, physicians are usually concerned if a patient has a QT-interval increase of about 30 msec from baseline, Shah noted. He acknowledges that this was a small study, but it did uncover a disturbing signal that needs to be further investigated.

Diastolic BP and heart rate increased nonsignificantly.

Although the 10-msec prolongation in the QT interval is a "small number, if it were consistently produced by a drug being considered by the FDA, the FDA would require more testing to make sure that there was not a liability for producing further, more serious, and life-threatening prolongation of the QT interval and associated arrhythmias," AHA spokesperson and past president Dr Gordon F Tomaselli (Johns Hopkins University, Baltimore, MD) commented.

Both Shah and Tomaselli pointed out that people who are older or who have underlying CVD might have even more heart-related side effects from energy drinks than the young, healthy people in this meta-analysis.

The authors had no conflict of interest related to this study.