Because the number of hospital visits and deaths related to consuming energy drinks has increased in recent years, researchers looked at how they affect the heart and blood pressure—and the findings may make physicians think differently.

Findings revealed that a 32-ounce energy drink with 320 milligrams of caffeine altered the heart’s electrical activity and blood pressure more than a 32-ounce control drink with the same amount of caffeine. The study was published in the Journal of the American Heart Association.

Though the U.S. Food and Drug Administration considers caffeine in doses of less than 400 mg safe, energy drinks usually include other ingredients that can prompt heart and blood pressure problems.

“We decided to study energy drinks’ potential heart health impact because previous research has shown 75 percent of the base’s military personnel have consumed an energy drink,” said Emily A. Fletcher, deputy pharmacy flight commander at the David Grant U.S.A.F. Medical Center at Travis Air Force Base in Fairfield, California, in a statement. “And nearly 15 percent of military personnel, in general, drink three cans a day when deployed, which is more than we studied here.”

In Fletcher’s study, 18 participants were randomly divided into two groups. One group drank a commercially available energy drink that contained 108 grams of sugar, 320 milligrams of caffeine and other various compounds. The other group consumed a control drink that had 320 milligrams of caffeine, 40 milliliters of lime juice and 140 milliliters of cherry syrup in carbonated water.

After six days, participants switched drinks and the researchers measured the electrical activity of their hearts. They also measured their blood pressure throughout the study.

Results showed that participants who drank the energy drink had a corrected QT interval 10 milliseconds higher at two hours than the caffeine group. Additionally, both groups had similar increases in systolic blood pressure, but levels in those who drank the control drink returned to their original readings after six hours.

“On the other hand, those who consumed the energy drinks still had a mildly elevated blood pressure after six hours,” Fletcher said. “This suggests that ingredients other than caffeine may have some blood pressure-altering effects, but this needs further evaluation.”