Energy drinks can give you a big boost when you’re feeling fatigued. But a new study from the American Heart Association suggests that the major lift could come at a cost to your heart’s electrical system and blood pressure—and it’s not even the abundance of caffeine in the drinks that’s the problem.
Six days later—after that one-time drink was believed to be fully “washed out” of the body—the groups switched drinks. Participants’ blood pressure and cardiac electrical activity were measured five times within 24 hours of beverage consumption.
Researchers found that those in the energy drink group had a faster QT interval, which is the time it take heart ventricles to generate a beat. When these intervals are too long or too short, it can cause the heart to beat abnormally.
In terms of blood pressure, those in both groups had similar increases in systolic pressure, but it took longer for the energy drinkers to return to their original readings. (Here’s how energy drinks also gave a man hepatitisnergy drinks also gave a man hepatitis.)
The researchers concluded that this means ingredients other than caffeine may be at play, but it will require further evaluation to tease out what’s causing the negative effects.
That could be challenging, since every brand claims it has a blend of proprietary ingredients. Two common ones include guarana—a form of Brazilian cocoa that also contains caffeine—as well as an amino acid, taurine. An Australian study in 2012 highlighted concerns about these ingredients as a mix, especially when they’re blended with alcohol or other stimulants.
Another hurdle is that the most recent study has limitations—especially in terms of sample size and duration. Having so few participants makes the findings less conclusive, and it’s not possible from this study to understand the long-term effects of energy drink consumption on the heart. Also, the study was done on healthy, young adults. It’s not known what the effect of these drinks may be on someone who already has heart issues.
More research will have to be done to confirm the results. But for now, the researchers suggest that people who have high blood pressure or underlying cardiac conditions may want to be especially cautious when consuming energy drinks.