Downing an energy drink may seem like the perfect fix when you’ve hit that mid-afternoon slump and still have an email inbox full of messages. But any boost you get may come at a cost: a higher risk of heart disease.

Mayo Clinic researchers measured blood pressure and levels of norepinephrine (a stress hormone) on two separate days in 25 healthy young people before and after consuming a beverage. On one day, the beverage was an energy drink that contained caffeine and taurine (an amino acid purported to increase physical and mental performance)—common ingredients in energy drinks—and extracts of guarana seed, ginseng, and milk thistle. On the other, it was a drink that matched the energy drink in taste, color, and nutritional content, but did not have the caffeine or other ingredients.  

The subjects' blood pressure increased by an average of 6.4 percent after they had the energy drink, compared to 1 percent after the placebo drink. Norepinephrine levels rose 73.6 percent versus 30.9 percent. “Previous research has shown this degree of blood pressure and norepinephrine changes are associated with an increase in cardiovascular risk several years later,” says Anna Svatikova, M.D. Ph.D., lead author of the study. “Some young people consume energy drinks regularly, and these repetitive changes in norepinephrine may be potentially harmful.”  

“There is nothing unique about the caffeine in mainstream energy drinks, which is about half that of a similar sized cup of coffeehouse coffee," The American Beverage Association said in a statement. "The safety of energy drinks has been established by scientific research as well as regulatory agencies around the globe."

Is Caffeine the Cause?

The caffeine content of both energy drinks and coffee varies. The drink used in the study had 240 milligrams of caffeine in 16 ounces. A 16-ounce cup of coffee has roughly 70 to 360 milligrams. Healthy adults can safely consume up to 400 milligrams of caffeine a day. Pregnant women should stick to 200 milligrams, and kids no more than 85 milligrams.

But energy drinks and coffee aren’t the only sources of the stimulant. Caffeine is being added to chocolate bars, gum, peanut butter, water, and other foods. The Food and Drug Administration is concerned about this trend, citing the lack of careful consideration of the cumulative impact caffeine-containing foods could have, especially on children and teens. The agency has announced that it will be investigating the safety of caffeine in food products, but currently while food manufacturers have to list it in the ingredients list, they don’t have to tell you how much caffeine is in the product. In 2012, Consumer Reports analyzed the caffeine content of 27 energy drinks. Sixteen of those listed the caffeine content on the label, and of those, five had more than 20 percent more caffeine that the label stated.

Still, it’s not clear if it is caffeine or some other ingredient in energy drinks that boost the odds of developing heart disease. “Although the physiological effects of some energy drink ingredients have been documented, others are unknown,” says Svatikova. “It may also be the combination of the ingredients that led to the observed effects.”  

What to Do

"The rising tide of adverse cardiovascular events associated with energy drinks calls for further research," says Svatikova. In the meantime, she urges caution when using these drinks. "Energy drinks may be silent dangers for the heart," she says "They may potentially increase the risk of heart problems, even among young people, and those with hypertension or arrhythmia may be even more predisposed to increased risk."