Findings gathered by a team from the US revealed that drinking a commercially available energy drink containing 320 milligrams (mg) of caffeine results in increased electrical heart activity and rises in blood pressure.
These findings were in comparison to test subjects consuming a control drink also containing 320 mg of caffeine along with 40 millilitres (ml) of lime juice and 140 ml of cherry syrup in carbonated water.
The conclusions suggest the proprietary energy blends used to create energy drinks that work in tandem with caffeine to produce these heightened effects.
Commenting on the study, author Dr Emily Fletcher observed that those who consumed the energy drinks still had a mildly elevated blood pressure after six hours.
"This suggests that ingredients other than caffeine may have some blood pressure altering effects, but this needs further evaluation," added Dr Fletcher, who is also deputy pharmacy flight commander at Travis Air Force Base in California.
With over 500 types of energy drinks on the market, the team commented that the increase in energy-drink-associated cases have prompted questions about their safety.
Energy drinks and exercise
With cases highlighting energy drinks’ links to hypokaleamia and recommendations not to consume them during physical exercise, European regulatory authorities may need to re-examine what impact these beverages have on long-term health.
Current European Food Safety Authority (EFSA) guidelines indicate that 400 mg of caffeine a day from all sources is not a safety concern.
The same direction also applies to single doses of up to 200 mg for adults (18-65 years). This level remained safe when consumed less than two hours before intense exercise.
"We decided to study energy drinks' potential heart health impact because previous research has shown 75% of the base's military personnel have consumed an energy drink,” said Dr Fletcher.
“Nearly 15% of military personnel, in general, drink three cans a day when deployed, which is more than we studied here," she added.
Dr Fletcher and colleagues enrolled 18 participants between 18 and 40 years of age, into two groups.
The first group received 32 ounces (oz) (946 millilitres (ml)) of energy drink containing 108 g of sugar, 320 mg caffeine, vitamin B2, vitamin B3, vitamin B6, and vitamin B12.
The drink also contained a proprietary energy blend of taurine, panax ginseng extract, L‐carnitine, glucuronolactone, inositol, guarana extract and maltodextrin.
The other group was given the control drink containing 32‐oz control drink containing 320 mg of caffeine, 40 mL of lime juice, and 140 ml of cherry syrup in carbonated water. After a six-days, participants switched drinks.
Electrical activity of the volunteers' hearts were measured as were their peripheral and central blood pressures at the study's start and at one, two, four, six and 24 hours after drink consumption.
When compared to the caffeine group, they found those in the energy drink group had a corrected QT interval 10-milliseconds higher at 2 hours.
“The QT interval is the measurement of the time it takes ventricles in the heart (the lower chambers) to repolarize, or prepare to generate a beat again. It's the pause from the end of the electrical impulse generating the heart to beat to the next impulse," Dr Fletcher explained.
"If this time interval, which is measured in milliseconds, is either too short or too long, it can cause the heart to beat abnormally. The resulting arrhythmia can be life threatening."
Additional findings revealed increases in systolic blood pressure were seen in the energy drink and caffeine-only groups.
However, systolic pressures in the caffeine group had almost returned to their original readings after six hours, not so for the energy drink group.
‘Findings are odd’
Responding to the findings, The British Soft Drinks Association’s (BSDA), director general Gavin Partington said: “Caffeine in energy drinks is no different to caffeine in coffee so these findings are somewhat odd.
“The European Food Safety Authority latest opinion confirms the safety of energy drinks and their ingredients and therefore does not provide any scientific justification to treat energy drinks any differently to the main contributors to daily caffeine intake including tea, coffee and chocolate.
“It’s also worth remembering that coffees from popular high street chains contain the same or more caffeine than most energy drinks.”
Source: Journal of the American Heart Association
Published online ahead of print: doi.org/10.1161/JAHA.116.004448
“Randomized Controlled Trial of High‐Volume Energy Drink Versus Caffeine Consumption on ECG and Hemodynamic Parameters.”
Authors: Emily Fletcher, Carolyn Lacey, Melenie Aaron, Mark Kolasa, Andrew Occiano, Sachin Shah