Downing energy drinks packed with caffeine actually causes your heart to pump more forcefully, according to researchers who are pretty sure that isn't a good thing. The heart researchers, who were trying to determine why the drinks are linked to tens of thousands of emergency room visits annually, gave volunteers drinks containing large amounts of caffeine and taurine, another key energy drink component, and found that their hearts were contracting harder within an hour, reports the BBC.
"We've shown that energy drink consumption has a short-term impact on cardiac contractility," the lead researcher says. "We don't know exactly how or if this greater contractility of the heart impacts daily activities or athletic performance," he says—but the team suggests children and people with irregular heartbeats steer clear of the drinks. The maker of Monster Energy drinks, however, calls the study "alarmist and misleading" and makes the case for the benefits of its drinks, notes the LA Times. Taurine boosts the pumping force of the heart without affecting blood pressure, and this is "widely considered to be beneficial," the company said in a statement. (Read more energy drinks stories.)