A small study doesn't expose direct cause and effect but suggests it's not the caffeine causing the observed change.
Study's energy drink arm had higher change in corrected QT interval
Drinking a high-volume energy drink was linked to more heart and blood pressure changes compared with a control drink containing the same amount of caffeine, according to a small crossover study of military personnel.
Those in the energy drink arm had a significantly higher change in corrected QT interval, a measure of cardiac repolarization, compared with those in the caffeine arm at 2 hours after baseline (0.44 ms versus 10.4 ms, P=0.02), reported Emily A. Fletcher, PharmD, of David Grant U.S.A.F. Medical Center at Travis Air Force Base Fairfield, Calif., and colleagues.
"Based on this preliminary evidence in young, healthy adults, people who have high blood pressure, underlying cardiac conditions or other health issues might want to avoid or use caution when consuming energy drinks until more is known about their impact on heart health," wrote the authors in the Journal of the American Heart Association.
John P. Morrow, MD, of Columbia University Medical Center in New York City, told MedPage Today that the study confirms previous findings that caffeine is probably safe in moderate doses.
"The bad news is that energy drinks may have concerning short-term effects on the cardiovascular system, although they are unlikely to cause serious side effects in healthy young people," said Morrow, who was not involved in the study.
Fletcher's group recruited 18 participants (12 men) via email and flyers from 2013 to 2014 on a U.S. Air Force Base installation. All participants were randomized to receive 32 oz of a commercially available energy drink or a control drink, both which contained 320 mg of caffeine. After a 6-day washout period, participants switched drinks.
The researchers collected ECG, peripheral blood pressure, and central blood pressure measurements at baseline and at 1, 2, 4, 6, and 24 hours after drink consumption.
Fletcher and colleagues found that changes in corrected QT intervals were different between the two groups after 2 hours, but not at other time points.
While both groups initially had similar increases in systolic blood pressure, a significant difference was evident after 6 hours in the energy arm but not the caffeine arm (4.72 mm Hg versus 0.83 mm Hg, P=0.01).
Additionally, the researchers reported a significant decrease in baseline-adjusted augmentation index after 6 hours in the energy drink arm compared with the caffeine arm ( 3.72 versus 1.50, P=0.02). No difference was seen with heart rate, diastolic blood pressure, central systolic blood pressure, and central diastolic blood pressure at any time point between the two groups (P>.07).
The authors concluded that the findings "suggest that ingredients other than caffeine may have some blood pressure altering effects, but this needs further evaluation."
Study limitations included the absence of a true placebo and that the results only appeared to be significant relative to the caffeine group.
Paul Eugenio, MD, of Montefiore Medical Center in New York City, who was not involved in the study, suggested that factors like the small sample size increase the probability that the study results were a "chance" finding.
However, "that being said, the results are of interest and serve as hypothesis generating for larger, more adequately powered studies to assess for a true effect of energy drinks on cardiac repolarization (the QT interval) and peripheral blood pressure," wrote Eugenio in an email.
Morrow agreed, noting that different energy drinks with different herbal or chemical ingredients may have different effects on the cardiovascular system.
"We cannot assume class effects, and we cannot assume that herbal/natural preparations are always safe. More work is needed, and we should not extrapolate these results to middle-age healthy people, or elderly people with heart disease," he told MedPage Today.
The study was funded by the Clinical Investigations Facility at Travis Air Force Base.
Fletcher and co-authors disclosed no relevant relationships with industry.
last updated 04.27.2017
Fletcher E, et al "Randomized controlled trial of high-volume energy drink versus caffeine consumption on ECG and hemodynamic parameters" J Am Heart Assoc 2017; DOI:10.1161/JAHA.116.004448.