Energy drinks, which have been linked to deaths and hospitalizations, may boost blood pressure and lead to an erratic heartbeat, a study found.
An analysis of seven previous studies showed the beverages appeared to disturb the heart's natural rhythm, which over time may lead to an irregular heartbeat or death and raise blood pressure. The findings were presented at the American Heart Association meeting in New Orleans.
The U.S. Food and Drug Administration and other regulators have been investigating the drinks made by companies including Monster Beverage Corp., Living Essentials LLC and Red Bull GmbH after they were linked to hospitalizations and death. The findings mean people, particularly those with pre-existing heart conditions, should be cautious when consuming the drinks, said Sachin Shah, the lead study author.
"We need to look at the effects of long-term energy drinks consumption and see what the consequences are," said Shah, an assistant professor of pharmacy practice at the University of the Pacific in Stockton, California, in a telephone interview.
"Everything is good in moderation. Drink them within the limits that have been provided and be vigilant of what else you're consuming with it."
The high caffeine content may be causing these heart changes or it could be another ingredient in the drinks, Shah said. More studies are needed though to look at the ingredients and their health effects, he said. The heart changes don't appear to be permanent, he said.
Energy drinks aren't bound by FDA guidelines for caffeine in sodas because they are often sold as dietary supplements. Soda typically can have as many as 71 milligrams of caffeine per 12 ounces, while caffeine in energy drinks often ranges from 160 milligrams to 500 milligrams a serving, the FDA said in a letter last year.
Doctors this week wrote FDA Commissioner Margaret Hamburg saying energy drinks should have no more caffeine than sodas and companies should be required to list caffeine content on labels. The letter was signed by 18 doctors from centers that included Johns Hopkins University School of Medicine and the University of Maryland School of Public Health.
Democratic Senators Richard Durbin of Illinois, and Richard Blumenthal of Connecticut, urged the FDA in December to convene an expert panel to discuss the effects of consumers' caffeine consumption. Durbin began pushing the FDA almost a year ago to more strictly regulate energy drinks.
Researchers evaluated 93 people from three studies after they consumed one to three energy drinks. They found that the QT interval, which is a segment of the heart's rhythm on an electrocardiogram, was 10 milliseconds longer after they consumed the drinks than before.
Shah said doctors become concerned if patients have an extra 30 milliseconds in their QT interval. Prolonging QT over the long term could lead to life-threatening arrhythmias, or irregular heartbeats.
The American Beverage Association, a U.S. trade group that represents makers of non-alcoholic drinks, declined to comment on the research. Shares of Corona, California-based Monster Beverage declined 3 percent to $48.85 in extended trading at 4:46 p.m. New York time after closing at $50.35.
QT Interval Gordon Tomaselli, past president of the American Heart Association and a professor of medicine at Johns Hopkins University in Baltimore, said in accompanying video that a typical QT interval is about 400 milliseconds. People who have had a heart attack or heart failure may already have a prolonged QT interval so adding another 10 milliseconds by consuming energy drinks could worsen their health. He suggests that patients with heart problems or who have a family history of heart disease might want to avoid these drinks.
"These energy drinks should be considered like we consider a medication," he said. "They have a series of pharmacologically active ingredients, natural or not.
They need to be treated with that level of respect." In another analysis of six trials and 132 patients, the researchers found that systolic blood pressure, the top number of the blood pressure reading that measures the pressure in the arteries when the heart beats, increased about 3.5 points on average. The findings are particularly concerning for people who consume these drinks frequently and those who have high blood pressure, Shah said.
"Patients with high blood pressure or long QT syndrome should use caution and judgment before consuming an energy drink," he said. "Since energy drinks also contain caffeine, people who do not normally drink much caffeine might have an exaggerated increase in blood pressure."