The study was presented to the American Heart Association's Scientific Sessions 2007 taking place in Orlando, Florida this week, and was carried out by Dr James Kalus, senior manager of Patient Care Services at Henry Ford Hospital in Detroit, Michigan, and colleagues.
Although the heart rate and blood pressure increases observed in this study were not dangerous for healthy volunteers, the results suggest the drinks could be dangerous to patients with heart disease, or if drinking more than two cans a day led to even higher increases, to healthy people too.
Kalus advised people with high blood pressure and heart rate to "avoid these drinks".
Energy drinks, unlike "sports" drinks that contain water, sugar and salts, have high levels of caffeine and taurine aimed at increasing "energy" or alertness. Taurine is an amino acid found in protein foods like meat and fish. Like caffeine, it has been shown to increase blood pressure and heart rate.
The researchers asked 15 healthy young adult volunteers (8 women and 7 men, average age 26 years) to stop consuming caffeine from other sources for two days before, and throughout the duration of the study.
On the first day of the study, they measured each volunteer's blood pressure and heart rate and also took an electrocardiogram (ECG) to assess heart function.
After that, the participants drank two cans of an energy drink containing 80 milligrams of caffeine and 1,000 milligrams of taurine, and this was followed by further blood pressure, heart rate and ECG measurements 30 minutes, one two, three and four hours later. This was repeated each day for the next five days, until the seventh day of the study when they repeated what they did on the first day.
In their analysis Kalus and colleagues compared the average at baseline (day 1) and day 7 with the peaks during the intervening 5 days.
The results showed that:
- Within 4 hours of consuming the energy drink, the maximum systolic blood pressure (the higher of the two blood pressure measures, when the heart compresses), increased by 7.9 per cent on day 1 and 9.6 per cent on day 7.
- Within 2 hours of consuming the energy drink, the maximum diastolic blood pressure (the lower of the two blood pressure measures, when the heart relaxes between beats) went up 7 percent on day 1 and 7.8 percent on day 7.
- Heart rate increased by 7.8 per cent on day 1 and 11 per cent on day seven.
- Over the period of the study, heart rates went up between 5 and 7 beats per minute and systolic blood pressure went up by 10 mm mercury (Hg) after having the energy drink.
- No significant ECG changes were observed.
"While energy drinks increase concentration and wakefulness, people with risk factors for heart disease could have a bad reaction. The subjects in this study were healthy with low blood pressure," he explained.
The researchers said they did not know what effect exercise or combining alcohol with energy drinks might have. However, they did say some countries advise people not to consume energy drinks while playing sports.
Blood pressure and heart rate rise naturally during intense physical exercise. These could go up even more with energy drinks said Kalus.
"Energy drinks could affect some individuals if they didn't know they had a problem in the first place," he added.
The researchers said their findings "raised concerns" and advised people with high blood pressure or heart disease keep off energy drinks because they could increase blood pressure or change the effect of any drugs they are taking.
Click here for American Heart Association.
Written by: Catharine Paddock