High-caffeine soft drinks may do more than give people a jolt of energy. They may also boost heart rates and blood pressure levels, researchers say.

The results of a small study prompted the researchers to advise people who have high blood pressure or heart disease to avoid energy drinks because they could impact their blood pressure or change the effectiveness of their medications.

The drinks generally have high levels of caffeine and taurine, an amino acid found in protein-rich foods like meat and fish that can affect heart function and blood pressure, the researchers say.

“We saw increases in both blood pressure and heart rate in healthy volunteers who were just sitting in a chair watching movies. They weren’t exercising. They were in a resting state,” says James Kalus of Henry Ford Hospital in Detroit, who led the study.

The increases did not rise to dangerous levels in the group of 15 healthy volunteers, whose average age was 26, the researchers say.

But the increases potentially could be significant in people with cardiovascular disease or those taking drugs to lower heart rate or blood pressure, they told a meeting of the American Heart Association in Orlando, Florida.

The American Beverage Association industry trade group defends the findings.

“While the amount of caffeine in energy drinks or coffee may cause a slight and temporary increase in blood pressure, it would have no greater effect than walking up a flight of steps,” it says in response to the study.

“So singling out energy drinks in a unique manner, particularly when compared to a more commonly consumed caffeinated beverage like coffee, does not provide a full and proper context for consumers.”

Kalus declined to say which brand of energy drink was used in the study. He says the drinks generally contain similar ingredients.

“By giving the brand, it would dilute the message that all of these drinks need to be looked at,” he says.

Drink then measure

The study participants were asked not to consume other forms of caffeine for two days before starting the study and then throughout a study, in which they drank two cans of energy drinks daily over seven days.

Each can contained 80 milligrams of caffeine and 1000 milligrams of taurine.

The volunteers’ heart rates rose by about 8% on the first day and 11% on the seventh day.

Maximum systolic blood pressure, the top number in blood pressure readings that represents pressure while the heart contracts, rose by 8% on the first day and 10% on the seventh day.

Diastolic blood pressure, the bottom number that gives the pressure when the heart relaxes between beats, rose by 7% on the first day and 8% on the seventh day.

The study did not identify ingredients responsible for the changes, but Kalus says it is probably caffeine and taurine.

Kalus says the study did not address possible health effects from the way some people consume these drinks, such as mixing them with alcohol.

Will Dunham
Reuters