Although trips to the emergency room linked to energy drinks almost doubled between 2007 and 2011, little was known about how the highly caffeinated beverages affected the heart.

Now, researchers say that healthy adults who downed the drinks, which are also high in the amino acid taurine, had increased heart contraction rates an hour later, according to a study presented Monday at the annual meeting of the Radiological Society of North America.

“We don’t know exactly how or if this greater contractility of the heart impacts daily activities or athletic performance,” said researcher and radiology resident Jonas Dörner, M.D., of the University of Bonn, Germany, in a news release. There are concerns about the products’ potential adverse side effects on heart function, especially in adolescents and young adults, but there is little or no regulation of energy drink sales.”

The researchers did a cardiac MRI on 18 healthy adults before and after consuming a caffeinated energy drink with taurine. The MRI revealed more peak strain in the heart’s left ventricle, where oxygenated blood flows from the lungs and is pumped to the aorta. There were no differences in heart rate or blood pressure.

“We’ve shown that energy drink consumption has a short-term impact on cardiac contractility,” Dörner said. “Further studies are needed to evaluate the impact of long-term energy drink consumption and the effect of such drinks on individuals with heart disease.”

The study is ongoing, but for now, researchers advise people with known cardiac arrhythmias to avoid energy drinks, hypothesizing that changes in contractility could provoke arrhythmias.

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