A study, published this week in the Journal of the American Heart Association (JAMA), concludes that consuming an energy drink produces more pronounced cardiovascular effects than a drink containing the same amount of caffeine.
Energy drinks have drastically risen in popularity over recent years. Today, there are more than 500 types of energy drinks on the market.
In 2006, the market was worth in the United States alone.
At the same time, the number of energy drink-related hospital visits and deaths has also increased.
Although the Food and Drug Administration (FDA) consider doses of caffeine under 400 milligrams to be safe, energy drinks contain a range of other substances.
These additives also have the potential to play a physiological role.
The latest study is authored by Emily A. Fletcher, deputy pharmacy flight commander from the David Grant U.S. Air Force Medical Center at Travis Air Force Base in California.
When asked why she chose to investigate these products, she answered: “We decided to study energy drinks' potential heart health impact because previous research has shown 75 percent of the base's military personnel have consumed an energy drink. And nearly 15 percent of military personnel, in general, drink three cans [per] day when deployed.”
Investigating energy drinks
The study involved 12 men and six women, all aged between 18 and 40 years.
They were randomly split into two groups.
The first group was given 32 ounces of a commercially available energy drink. This product contained 108 grams of sugar, 320 milligrams of caffeine, and a range of other compounds.
The other group received a drink containing the same quantity of caffeine, 40 milliliters of lime juice, 140 milliliters of cherry syrup, and carbonated water.
Six days later, the participants returned for a second trial and were given the other drink.
To assess the effects of the beverage, the team measured the electrical activity of the participants’ hearts using an electrocardiogram.
They also measured peripheral and central blood pressures at the start of the study and then at one, two, four, six, and 24 hours after consuming the drink.
Fletcher explains the difference between peripheral and central blood pressure: "Peripheral blood pressure is the measurement of the pressure in an outlying artery, typically an upper arm. Central blood pressure is the measurement of the pressure in the aorta near the heart.”
She goes on to explain that: “Blood pressures at each location are not always affected equally when a substance is introduced, such as medications. Central blood pressure is an emerging and potentially superior method to assess health outcomes related to elevated blood pressure."
Effects of an energy drink on the heart
At the two-hour mark, when compared with the control group, the energy drink group showed some significant differences.
Namely, they had a corrected QT interval 10 milliseconds higher.
The QT interval is a measure of the time that it takes for the lower chambers of the heart (or the ventricles) to repolarize, ready for the next beat. It is the pause between the end of an electrical impulse and the start of the next.
If this gap is too short or too long, it can produce an abnormal heartbeat – known as arrhythmia.
Although a 10-millisecond difference does not sound like a lot, it is a significant shift. For instance, if a medication affects the corrected QT interval by just 6 milliseconds, there will be a warning on the product’s label to that effect.
When comparing systolic blood pressure across the two groups, there was little difference. However, within six hours, the control group’s readings had almost returned to normal.
This was not the case in the energy drink group, as Fletcher explains: “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.”
Fletcher concludes that, although these are preliminary findings on a relatively small sample, people who have underlying cardiac conditions, high blood pressure, or other health issues might want to be cautious about consuming these types of drinks.