Researchers conducted the largest controlled study yet of the effects of energy drinks on the heart and blood pressure in healthy adults.

While still a relatively small study, new research published in the Journal of the American Heart Association is still the largest controlled study looking at how energy drinks affect the heart.

And we will just cut to the chase here with what the researchers found:

Drinking an energy drink in a short timespan may increase blood pressure and the risk of electrical disturbances in the heart, which affect heart rhythm.

Given that some 30 percent of American teenagers between the ages of 12 and 17 consume energy drinks on a regular basis – which has been linked to increased emergency room visits and death (!) – this seems like pretty relevant news.

The study included 34 healthy participants ranging in age from 18 to 40 years. They either drank 32 ounces of one of two commercial caffeinated energy drinks or a placebo. They drank the drinks evenly paced during the course of an hour.

The energy drinks included between 304 to 320 milligrams of caffeine per 32 fluid ounces. For reference, less than 400 milligrams of caffeine is not expected to induce any electrocardiographic changes – indicating that other ingredients, or a combination thereof, are at play. Other ingredients in the study’s energy drinks included taurine, glucuronolactone, and B-vitamins.

Electrocardiograms measured the electrical activity of the participants’ hearts, and blood pressure was taken as well, at the beginning and then every 30 minutes for four hours after the drinks were consumed.

“In participants who consumed either type of energy drink, researchers found that the QT interval was 6 milliseconds or 7.7 milliseconds higher at 4 hours compared to placebo drinkers,” notes the American Heart Association. “The QT interval is a measurement of the time it takes ventricles in the heart (the lower chambers) to prepare to generate a beat again. If this time interval is either too short or too long, it can cause the heart to beat abnormally. The resulting arrhythmia can be life-threatening.”

They also found a statistically significant 4 to 5 mm Hg increase in systolic and diastolic blood pressure in the energy drink drinkers.

“We found an association between consuming energy drinks and changes in QT intervals and blood pressure that cannot be attributed to caffeine. We urgently need to investigate the particular ingredient or combination of ingredients in different types of energy drinks that might explain the findings seen in our clinical trial,” said lead author Sachin A. Shah, Pharm.D., professor of pharmacy practice at University of the Pacific, Thomas J. Long School of Pharmacy and Health Sciences in Stockton, California.

The authors note that these results don’t take into consideration the fact that energy drinks are often consumed in combination with alcohol and/or other substances.

“Energy drinks are readily accessible and commonly consumed by a large number of teens and young adults, including college students. Understanding how these drinks affect the heart is extremely important,” said study co-author Kate O’Dell, Pharm.D., professor of pharmacy and director of experiential programs at the Thomas J. Long School of Pharmacy and Health Sciences.

For more, see the full study here: Impact of High Volume Energy Drink Consumption on Electrocardiographic and Blood Pressure Parameters: A Randomized Trial.