SAN FRANCISCO — A new study has found that consuming alcohol, even as little as one can of beer or one glass of wine, can quickly increase the risk of a common type of cardiac arrhythmia known as atrial fibrillation in people who have a history of the condition.

Doctors have long suspected a link between alcohol and atrial fibrillation, but until now, they did not have definitive evidence that alcohol could cause arrhythmias. The new study is among the most rigorous to date: The researchers recruited 100 people with a history of atrial fibrillation and tracked them intensely for four weeks, monitoring their alcohol intake and their cardiac rhythms in real time.

The scientists found that drinking alcohol heightened the odds that a person would have an episode of atrial fibrillation, or an abnormal heart rhythm, within the next few hours. And the more they drank, the greater their likelihood of having an arrhythmia.

The new study was published Monday (Sept 6) in the Annals of Internal Medicine. The conclusions, along with data from previous studies, suggest that people with a history of atrial fibrillation could reduce their chances of developing arrhythmias by cutting back on alcohol or avoiding it altogether.

The authors speculated that the findings could have broader implications for healthy adults as well. Although moderate drinking is widely considered beneficial for heart health, the new research suggests that, at least in some people, it could potentially disrupt how the heart functions.

“This demonstrates that whenever we consume alcohol, it is presumably having a nearly immediate effect on the electrical workings of our hearts,” said Dr Gregory Marcus, an author of the study and a professor of medicine in the division of cardiology at the University of California, San Francisco.

Atrial fibrillation, also known as A-fib, is the most commonly occurring heart rhythm abnormality, affecting an estimated three million adults in the United States. It occurs when the upper chambers of the heart, the atria, start beating irregularly, which can disrupt blood flow to the lower chambers of the heart, called the ventricles.

Over time, it can lead to complications like heart failure and strokes. A-fib can be persistent, or it can occur sporadically, with symptoms such as palpitations, shortness of breath and fatigue that last for a few minutes or hours at a time. When the episodes occur occasionally, the condition is known as paroxysmal atrial fibrillation.

People have a greater chance of developing atrial fibrillation as they get older. It’s also more likely to occur in people who have risk factors such as high blood pressure, heart disease, obesity, European ancestry or a family history of arrhythmias.

About four decades ago, doctors began documenting cases of people experiencing arrhythmias after bouts of heavy drinking on weekends and holidays, a phenomenon that came to be known as holiday heart syndrome. Since then, a number of large observational studies have found that people who regularly consume alcohol, even as little as one drink a day, have an increased likelihood of going on to develop atrial fibrillation compared with people who abstain.

Many of these previous studies had important weaknesses. In most cases, they relied on people self-reporting their alcohol intake, which is not always reliable. Studies have found for example that people tend to underestimate how much they drink. Another limitation is that people who are asked to recall an episode of atrial fibrillation can mistakenly identify a variety of behaviours as triggers.

The new study, however, was designed to get around those limitations. Dr Marcus and his colleagues recruited 100 people with a history of paroxysmal atrial fibrillation, most of them men, and had them wear electrocardiogram monitors that tracked their cardiac rhythms around the clock.

The devices contained a button that the participants were told to press any time they had an alcoholic beverage. The researchers used other, objective measures to track alcohol intake as well. They fitted the participants with special ankle monitors that could detect their blood alcohol levels.

And they did routine finger-stick blood tests to measure participants’ levels of phosphatidylethanol, or PEth, a biomarker that gives some indication of a person’s recent alcohol consumption.

During four weeks of tracking, the researchers found that at least 56 participants had experienced an episode of atrial fibrillation. The data indicated that alcohol was often a trigger for arrhythmias.

Having one drink doubled a person’s odds of having an episode of atrial fibrillation over the next four hours, while having two or more drinks tripled the odds of an event. The higher a person’s blood alcohol concentration, the greater their likelihood of having an arrhythmia.

Dr Mariann R. Piano, a researcher who has published many studies on alcohol and cardiovascular health, and who was not involved with the new study, said that the findings represent an important step forward in our understanding of how alcohol affects the heart.

She said that health care providers should have conversations with their patients, especially those who have atrial fibrillation, about how much alcohol they consume and whether it would be prudent for them to cut back or avoid it.

“Atrial fibrillation is an arrhythmia that can have life-changing effects, like having a stroke, and so understanding what might be an acute trigger is really important to communicate to our patients,” said Dr Piano, a professor and associate dean for research at the Vanderbilt University School of Nursing.

“Drinking is something that we can both monitor and modify on an individual basis. It’s something that we can easily be mindful of.”

But she called the study rigorous and added that the findings were timely because the prevalence of atrial fibrillation is quickly rising. According to the Centers for Disease Control and Prevention, an estimated 12.1 million people in the United States are expected to have atrial fibrillation by 2030.

Dr Piano said that health care providers should help their patients who consume alcohol understand how to engage in what the National Institute on Alcohol Abuse and Alcoholism defines as “low risk drinking”.

For women, it means having no more than three drinks on any single day and a maximum of seven drinks in a week. For men, low risk drinking means a maximum of 14 drinks per week and no more than four drinks on any single day.

The US federal government defines a standard drink as 12 ounces (355ml) of regular beer, 5 ounces of wine, or 1 1/2 ounces of distilled spirits (40 per cent alcohol).

Dr Marcus at UCSF said that the findings were potentially empowering for people with atrial fibrillation because they suggest that there is a way for them to control an important trigger of arrhythmias.

“This shows that these atrial fibrillation events are not simply due to random chance, and that there are modifiable factors that can be harnessed to reduce the chances that an event will occur,” he said.

Of course, this doesn’t mean that everyone who drinks will go on to have heart problems. But for those without a history of atrial fibrillation, he said, the findings should serve as a caution against excessive drinking, because it appears that alcohol can interfere with the heart’s electrical properties.

This article originally appeared in The New York Times.