Your doctor may have cautioned that the caffeine in coffee can set your heart racing and cause an abnormal heartbeat. Well, that's bunk, a new study finds.
"We were unable to find any evidence that those who drank coffee had a higher risk of developing abnormal heart rhythms. That's especially relevant because a common reason that health care providers recommend avoiding coffee is precisely to avoid abnormal heart rhythms," said lead researcher Dr. Gregory Marcus.
In fact, coffee may reduce the risk for future atrial fibrillation (a-fib) and other arrhythmias, said Marcus, a professor of atrial fibrillation research at the University of California, San Francisco.
Arrhythmia refers to an improper beating of the heart -- either too fast, too slow or erratically. Untreated arrhythmias can lead to cardiac arrest and stroke, according to the American Heart Association.
For the study, Marcus and his colleagues collected data on nearly 300,000 people in the U.K. Biobank, a long-term study in Britain. Average age of participants was nearly 57.
Over five years of follow-up, more than 13,000 people developed an arrhythmia. This included more than 4,700 with atrial fibrillation or atrial flutter, nearly 800 with supraventricular tachycardia, nearly 400 with ventricular tachycardia, and more than 300 with premature ventricular complex.
Compared with not drinking coffee, having up to 5 or more cups a day actually lowered the risk for any of these arrhythmias, the researchers found. Moreover, every additional cup lowered the risk 3%.
Marcus said that coffee might be good for you. It contains antioxidants, improves metabolism, enhances exercise performance and increases alertness and concentration.
A regular coffee habit may also lower the risk of heart disease and stroke.
Still, the study only observed an association. And there may be exceptions, especially for someone with an existing heart rhythm abnormality.
"It has been a concern for a long time that caffeine can cause heart rhythm problems, so reading this is reassuring in some ways, but I think what the lay public always needs to do is understand what research studies show and don't show," said Dr. Laurence Epstein, system director of electrophysiology at Northwell Health in Manhasset, N.Y. He was not part of the research.
What this study shows is that people who drank coffee had a lower risk of heart rhythm problems. "And that's fine, but one of the things we know, and we found over the years, is that each patient is different," Epstein said.
"There are some patients who can tell you triggers for atrial fibrillation, and there are others who can't," he said. "There are some people for whom caffeine is a definite trigger that if they drink any coffee or chocolate or anything with caffeine, it produces atrial fibrillation, but for other people, it has no effect."
People need to know their own body, and it's always best not to overdo, Epstein said.
"Moderation is always the key," he said.
Marcus agreed that for those who already have an irregular heartbeat, caffeine could trigger a-fib.
Heart patients should watch their reaction to caffeine, he noted.
"The primary goal when we treat patients with an arrhythmia is to help them with their quality of life, to help them feel well to do the things they want to do," Marcus said.
"If coffee is interfering with that, that's a reason to cut back, but if coffee is helping them with that and they're not experiencing any related adverse effects, then these data suggest it's safe to go ahead and enjoy your coffee," he added.
The results of the study were scheduled for presentation at the meeting of the Heart Rhythm Society, which was canceled due to the coronavirus epidemic. Data and conclusions released prior to peer review are generally considered preliminary.
For more on caffeine, see the Mayo Clinic.