Lots of us turn to energy drinks to pep us up when we’re feeling a little lethargic, but guzzling down large quantities of the caffeine-loaded fizzy stuff in a short time could potentially play havoc with our hearts, a study at Thomas J. Long School of Pharmacy and Health Sciences in Stockton, California, has found.

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The researchers gathered together 34 healthy volunteers between the ages of 18 and 40 and randomly assigned to drink two 500ml cans of one of two commercially available caffeinated energy drinks or a placebo drink on three separate days. The drinks were consumed within a 60-minute period but no faster than one can in 30 minutes.

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Both energy drinks tested contained between 152 and 160 milligrams of caffeine per can, an amount not expected to induce any changes in heart rhythms. Other common ingredients in the energy drinks in the study included taurine - an amino acid - glucuronolactone (found in plants and connective tissues) and B-vitamins. The placebo drink was made from carbonated water, lime juice and cherry flavouring.

They then monitored the electrical activity of the volunteers' hearts using an electrocardiogram, which records the way a heart is beating, every 30 minutes for four hours after the volunteers finished their drinks. They were specifically interested in changes in the QT interval - a measurement of the time it takes the lower chambers in the heart to prepare to generate a beat again. If this time interval is either too short or too long, it can cause the heart to beat abnormally. The resulting arrhythmia can be life-threatening.

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In participants who consumed either type of energy drink, researchers found that the QT interval was 6 milliseconds or 7.7 milliseconds higher at four hours compared to placebo drinkers – a significant difference.

“We found an association between consuming energy drinks and changes in QT intervals and blood pressure that cannot be attributed to caffeine. We urgently need to investigate the particular ingredient or combination of ingredients in different types of energy drinks that might explain the findings seen in our clinical trial,” said professor Sachin A. Shah. “The public should be aware of the impact of energy drinks on their body especially if they have other underlying health conditions. Healthcare professionals should advise certain patient populations, for example, people with underlying congenital or acquired long QT syndrome or high blood pressure, to limit or monitor their consumption.”


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Authors

Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.

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