A number of studies have shown that caffeinated energy drinks can raise blood pressure. Now a small study in the Journal of the American Heart Association provides more reason to be wary of these beverages, especially if you are at elevated cardiovascular risk: Drinking large volumes of them can prolong the QT interval, a measure of the heart’s electrical activity. A prolonged QT interval increases the risk of dangerous and possibly fatal arrhythmias.
Researchers randomly assigned 34 healthy young adults to drink 32 ounces of either of two brands of a caffeinated energy drink or a noncaffeinated placebo beverage (containing carbonated water, lime juice, and cherry flavoring) on three separate days. The energy drinks contained a combination of caffeine (304 to 320 milligrams per 32 ounces), B vitamins, and other substances.
Compared with the placebo beverage, the energy drinks significantly prolonged the QT interval over the four hours following consumption. Consistent with earlier research, the energy drinks also raised systolic and diastolic blood pressure more than the placebo (a difference of five and four points, respectively).
Interestingly, while the researchers attributed the blood pressure changes mainly to the beverages’ caffeine content, they surmised that the QT interval changes were likely related to the products’ mix of caffeine and other ingredients, which may interact in ways not yet understood.
It’s not clear what the long-term effects of the observed changes might be, nor whether the findings would apply to smaller amounts of the beverages. But according to the authors, “individuals with acquired or congenital long QT syndrome and those with hypertension should be more vigilant and limit their energy drink intake.”
Energy drinks have been linked in recent years with more than three dozen deaths and hundreds of other adverse events, including seizures and cardiac arrests. There is no reason to drink them. Pregnant women, children, teenagers, and people who are sensitive to caffeine should especially avoid them.