Energy drinks that contain large amounts of caffeine and other ingredients designed to put some “pep in your step” may also be giving your heart a jolt, too—but not in a good way.
New research set to publish next month in the journal Food and Chemical Toxicology found that heart cells exposed to some energy drinks had adverse reactions, including speeding up heart rate and negatively affecting cardiac function. Looking at 17 widely available brands, researchers used samples of the heart cells, called cardiomyocytes, and treated them with each drink to observe differences in how the cells reacted. (Related: 15 Underrated Weight Loss Tips That Actually Work).
Believe it or not, caffeine wasn’t the biggest issue. The cardiomyocytes had the most adverse reaction to three common ingredients in these drinks: theophylline, adenine, and azelate. Because energy drinks aren’t regulated, manufacturers can use these ingredients to whatever degree they want—and it’s tough for consumers to know how much they’re ingesting since additives like this might be grouped into the category of “proprietary blend.”
Although the recent study used cells instead of human participants, other studies have found similar results with people. For example, a study published in the Journal of the American Heart Association recruited 34 healthy people between the ages of 18 and 40 and gave half of them 32 ounces of commercially available energy drinks on three separate days.
Compared to the placebo group, the energy drink participants showed higher QT intervals—the time it takes the lower chambers of your heart to prep for a beat— even four hours later. That’s important because if the interval is too short or too long, it can cause arrhythmia, a condition where the heart beats abnormally. Those in the energy drink group also had a significant increase in systolic and diastolic blood pressure, researchers noted.
“The effects we saw were temporary, and not enough to shock the heart,” says the lead author of that study, Sachin Shah, Pharm.D., professor of pharmacy practice at the University of the Pacific. “But that said, drinking a large amount within a short period of time should be avoided, especially if you have underlying heart issues.”
That advice is backed up by the World Health Organization, which has called energy drinks a potential danger to public health even as sales have soared. An occasional energy drink, especially in a modest amount, isn’t likely to make your heart go haywire, Shah says. But if you’re drinking them regularly, you may want to rethink your go-to energy fix.
Now, make sure to read 12 Dangerous Side Effects of Energy Drinks, According to Science.