Energy drinks are consumed by many Americans on a regular basis. A new study by researchers at the Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota, has found that consumption of energy drinks can jeopardize cardiovascular health. The findings were published online in the Journal of the American Medical Association (JAMA) on November 8.
The study authors note that energy drink consumption has been associated with serious cardiovascular events, which are possibly related to caffeine and other stimulants. They theorized that drinking a commercially available energy drink compared to a placebo drink increases blood pressure and heart rate in healthy adults at rest as well as in response to mental and physical stress. In addition, they proposed that these hemodynamic (blood circulation-related changes are associated with activation of the sympathetic nervous system, which could increase cardiovascular risk. Stimulation pf the sympathetic nervous system occurs in a “fight or flight” situation (e.g., an intruder breaking into your home).
The study group comprised 25 healthy volunteers aged 18 years or older, who were nonsmokers, free of known disease, and not taking medications. The investigators conducted a randomized, double-blind, placebo-controlled, crossover pilot study: a study in which the participants were randomly assigned to receive either a placebo or energy drink; the two groups were then switched; and neither the participants nor the researchers were aware of who was receiving the energy drink. Each participant consumed either one can (480 mL; 16 oz) of a commercially available energy drink (Rockstar; Rockstar Inc.) or a placebo drink within 5 minutes, in random order on two separate days, a maximum of two weeks apart. The placebo drink, selected to match the nutritional elements of the energy drink, was similar in taste, texture, and color but lacked caffeine and other stimulants of the energy drink (240 mg of caffeine, 2000 mg of taurine, and extracts of guarana seed, ginseng root, and milk thistle).
Twenty-four hours before each study day, the subjects were fasting and abstained from caffeine and alcohol. Blood was drawn for serum levels of caffeine, plasma glucose, and norepinephrine, and blood pressure and heart rate were measured at baseline and 30 minutes after drink consumption. Hemodynamic measurements were also obtained during a two-minute physical, mental, and cold stressors performed in that order with 10-minute recovery times. Physical stress was achieved by asking participants to sustain an isometric handgrip of one-third of maximum voluntary handgrip contraction, using a dynamometer. During mental stress, the participants were required to complete serial mathematical tasks as fast as possible. During the cold-pressor test, performed last because of its long-lasting effects, participants immersed one hand into ice water.
The investigators found that caffeine levels remained unchanged after consumption of the placebo, but increased significantly after energy drink consumption. Glucose levels increased similarly between the groups. Baseline blood pressure and heart rate were normal and similar for participants on both the energy drink and placebo study days. Consumption of the energy drink produced a 6.2% increase in systolic blood pressure (from 108.4 mm Hg to 115.0 mm Hg) vs. a 3.1% increase with the placebo (from 108.3 mm Hg to 111.6 mm Hg). Diastolic blood pressure increased by 6.8% vs. 0% with the placebo Average blood pressure increased after consumption of the energy drink by 6.4% from 74.2 mm Hg to 78.9 mm Hg vs by 1.0% with the placebo drink (from 74.9 mm Hg to 75.4 mm Hg). There was no significant difference in heart rate increase between the two groups. The energy drink did not further increase hemodynamic responses to any stress stimuli. The average norepinephrine level increased from 149.8 pg/mL to 249.8 pg/mL after consumption of the energy drink and from 139.9 pg/mL to 178.6 after the placebo (change rate: 73.6% vs. 30.9%).
The authors concluded that a commercially available energy drink significantly increased levels of blood pressure and catecholamines (stimulant hormones) in young healthy adults. Physical, mental, or cold stress did not further heighten the blood pressure increase. These acute hemodynamic and adrenergic changes may predispose to increased cardiovascular risk.