A single can of an energy drink packs quite a wallop, causing potentially worrisome spikes in blood pressure and in a stress hormone that's a cousin to adrenaline, say researchers at the Mayo Clinic. Reporting in the journal JAMA, the Mayo team recruited 25 healthy adults for the study and measured the volunteers' blood pressure, heart rate, and levels of caffeine, glucose, and the hormone norepinephrine in their bloodstream before and after ingesting the energy drink Rockstar. They simultaneously tested a placebo that looked and tasted similar but lacked the caffeine and stimulants such as taurine and milk thistle extract found in the energy drink, the researchers report in a press release.
While heart rate didn't change significantly after a person drank one serving of Rockstar, average blood pressure increased by 6.4%, while average norepinephrine levels went up 31% after taking the placebo versus 74% after downing the energy drink. "These acute hemodynamic and adrenergic changes may predispose to increased cardiovascular risk," they write. The same group had earlier this year found that energy drinks can raise blood pressure to potentially unhealthy levels, reports Live Science, though they warn that larger studies will be required to confirm this study's results because the sample size is so small and involved just one type of energy drink. (Little evidence backs up the claim by energy drink makers that ingredients other than caffeine increase energy levels.)