Small, early study found contraction rate sped up after people downed beverage.

Energy drinks may provide a bit too much of a boost to your heart, creating additional strain on the organ and causing it to contract more rapidly than usual, German researchers report.

Healthy people who drank energy drinks high in caffeine and taurine experienced significantly increased heart contraction rates an hour later, according to research scheduled for presentation Monday at the annual meeting of the Radiological Society of North America, in Chicago.

The study raises concerns that energy drinks might be bad for the heart, particularly for people who already have heart disease, said Dr. Kim Williams, vice president of the American College of Cardiology.

"We know there are drugs that can improve the function of the heart, but in the long term they have a detrimental effect on the heart," said Williams, a cardiology professor at Wayne State University School of Medicine, in Detroit.

For example, adrenaline can make the heart race, but such overexertion can wear the heart muscle down, he said. There's also the possibility that a person could develop an irregular heartbeat.

From 2007 to 2011, the number of emergency room visits related to energy drinks nearly doubled in the United States, rising from slightly more than 10,000 to nearly 21,000, according to a meeting news release. Most of the cases involved young adults aged 18 to 25, followed by people aged 26 to 39.

In the new study, researchers used magnetic resonance imaging (MRI) to measure the heart function of 18 healthy participants both before and one hour after they consumed an energy drink.

The energy drink contained 400 milligrams of taurine and 32 milligrams of caffeine per 100 milliliters of liquid (about 3.4 ounces). Taurine is an amino acid that plays a number of key roles in the body, and is believed to enhance athletic performance. Caffeine is the natural stimulant that gives coffee its kick.

After downing the energy drink, the participants experienced a 6 percent increase in their heart contraction rate, said study co-author Dr. Jonas Doerner, a radiology resident in the cardiovascular imaging section at the University of Bonn, in Germany.

It appears that the unique blend of sugar, caffeine and taurine in an energy drink may combine to have an effect on the heart, Doerner said. He and his colleagues tested a second group using a drink containing only caffeine, but those patients did not show a significant increase in heart contractions.

"Maybe the mechanism could be from the taurine, or from the combination of taurine and caffeine," he said.

Because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

The American Beverage Association responded to the study with a prepared statement.

"The fact remains that most mainstream energy drinks contain only about half the caffeine of a similar size cup of coffeehouse coffee," the industry group said. "Caffeine is a safe ingredient and is consumed every day in a wide variety of foods and beverages, including energy drinks which have been enjoyed safely by millions of people for nearly three decades. Also, this paper, which looks at only 18 adults, has not been peer-reviewed or published."

Doerner was reluctant to speculate on potential damage to the heart that could result from long-term energy drink consumption, given that his study focused only on short-term effects.

"We have shown that even small amounts of energy drinks alters heart function," he said. "Because of that, further investigation needs to be done to address concerns regarding long term effects on kids and long-term effects on people with heart disease."

However, Doerner did advise that children and people who have an irregular heart beat should avoid energy drinks until more study is done.

Cardiology professor Williams agreed that further research is needed, adding that these results need to be followed up.

"Without data, one can only speculate," he said. "If you speculate on existing drugs that have that effect, it would be cause for concern."

SOURCES: Jonas Doerner, M.D., radiology resident, cardiovascular imaging section, University of Bonn, Germany; Kim Williams, M.D., vice president, American College of Cardiology, and cardiology professor, Wayne State University School of Medicine, Detroit; Dec. 2, 2013, statement, American Beverage Association; Dec. 2, 2013, presentation, Radiological Society of North America annual meeting, Chicago