Makers of energy drinks, meanwhile, have insisted the beverages are safe and that some of the cases of bad reactions may have been due to pre-existing conditions the individuals in question had.
In an effort to get more information about exactly happens in the human body after consuming one of the drinks, Mayo Clinic researcher Anna Svatikova and her colleagues recruited 25 volunteers.
All were young adults age 18 or older, nonsmokers, free of known disease and not taking medications. They were asked to drink a 16-ounce can of a Rockstar energy drink and a placebo with the same taste, texture, color and nutritional contents but without the caffeine and other stimulants within five minutes on two separate days.
The energy drink had the following stimulants: 240 mg of caffeine, 2,000 mg of taurine and extracts of guarana seed, ginseng root and milk thistle.
Researchers took numerous measurements first before subjects drank and 30 minutes after. With the placebo, there was very little change. With the energy drink, however, many changes were marked:
Systolic blood pressure (the top number): 6.2 percent increase.
Diastolic blood pressure (the bottom number): 6.8 percent increase.
Average blood pressure: 6.4 percent increase.
Caffeine in blood: Increase from undetectable to 3.4 micrograms/milliliter.
Norepinephrine level (the stress hormone, which can give you the shakes when you have too much caffeine) in blood: Increase from 150 picograms/milliliter to 250 pg/ml.
Writing in JAMA, the researchers said these changes may predispose those who drink a single drink to increased cardiovascular risk.
This may explain why a number of those who died after consuming energy drinks appeared to have had heart attacks.
The physical stressor involved asking participants to squeeze a handgrip; the mental one was to complete a serial mathematical tasks as fast as possible and the cold test, was to immerse one hand into ice water. Interestingly, there was no further change.