Caffeinated energy drinks can increase the heart's contraction rates in healthy people, according to a new study.
While the potential health risks of this effect are still not known, researchers said the findings suggest people who have cardiac arrhythmia should avoid these drinks because arrhythmia could be triggered by changes to the heart's contraction rates.
"We've shown that energy drink consumption has a short-term impact on cardiac contractility," study researcher Jonas Dörner, M.D., of the University of Bonn, said in a statement. "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 was presented at the annual meeting of the Radiological Society of North America; because it has yet to be published in a peer-reviewed journal, its results should be regarded as preliminary.
For the study, researchers from the University of Bonn recruited 18 healthy people -- 15 men and three women -- with an average age of 27.5 to undergo cardiac magnetic resonance imaging before drinking an energy drink containing 32 milligrams/100 milliliters of caffeine and 400 milligrams/100 milliliters of taurine.
Then, an hour after consuming the drinks, all the participants underwent cardiac MRI to see if energy drink consumption had any effect on heart function. The researchers found that the participants' hearts had increased contraction rates -- indicated by increased peak systolic strain in the heart's left ventricle -- after drinking the energy drinks.
They did not find that drinking the energy drink had any impact on blood pressure, heart rate or ejection of blood from the left ventricle.
However, past research has shown a link between energy drink consumption and negative effects on blood pressure. Research presented at an American Heart Association meeting this year examined data from seven other studies, and found that energy drink consumption seemed to increase systolic blood pressure (the top number in a blood pressure reading), as well as increase the QT interval by 1 milliseconds.
A QT interval is "a measurement made from the ECG [electrocardiogram] of the time from the onset of the electrical wave in the heart to when the entire heart has reset and is ready for the next beat," according to Duke Health. A longer QT interval is a known risk factor for dangerous arrhythmia.
Energy drinks have been linked with a number of recent deaths and hospitalizations, including the death of 14-year-old Anais Fournier, who died after drinking two Monster drinks in a 24-hour-period. Fournier had a heart condition called mitral valve prolapse; after drinking the energy drinks (which had a combined 480 milligrams of caffeine), the Maryland teen went into cardiac arrest and died from cardiac arrhythmia due to caffeine toxicity.
While 400 milligrams of caffeine a day is regarded as a safe amount of caffeine consumption for adults (equivalent to four to five cups of coffee), the Food and Drug Administration noted that there is no set "safe" level for children, though kids and teens are discouraged from caffeine consumption by the American Academy of Pediatrics. A recent study from University of Miami researchers also noted that kids will find no benefit from energy drinks, and that they could potentially be dangerous.
The FDA announced earlier this year that it is investigating the safety of food and drink products that have caffeine added to them, particularly their effects on kids and teens. Right now, FDA requirements for companies adding caffeine to their products is as follows:
Manufacturers can add it to products if they decide it meets the relevant safety standards, and if they include it on the ingredient list. While various uses may meet federal food safety standards, the only time FDA explicitly approved adding caffeine was for colas in the 1950s. Existing rules never anticipated the current proliferation of caffeinated products.