Is Coffee Bad for the Heart? What a New Trial Says About Coffee and Atrial Fibrillation

Written by Michael Bronfman, for Metis Consulting Services

December 1, 2025

If you have heart rhythm issues, ditch the caffeine, is good advice, right? Not necessarily. A groundbreaking new trial challenges that long-held belief with surprising evidence. Read the full article below in this week’s Guard Rail:” Your morning cup might be safe—and possibly even good for you and your heart.

Is Coffee Bad for Irregular Heartbeat?

For many years, people have heard that coffee is bad for the heart. Doctors often warn patients with heart rhythm problems to stay away from caffeine because it might trigger an irregular heartbeat. This belief has been part of common medical advice for decades. Coffee is one of the most popular drinks in the world, and many people depend on it to start their day. As a result, the question of whether coffee harms or benefits the heart has become very important for both patients and clinicians.

A new randomized clinical trial offers an answer to a question that has not been thoroughly studied before. The study asked a simple but essential question. Does drinking caffeinated coffee help, harm, or not affect the risk of having another episode of atrial fibrillation after a patient has been treated for it?

What is Atrial Fibrillation?

Atrial fibrillation is a common heart rhythm disorder. In atrial fibrillation, the top chambers of the heart beat in a fast and irregular way. This can cause symptoms such as shortness of breath or chest discomfort. It can also increase the risk of stroke. Many people who have atrial fibrillation undergo a procedure called cardioversion. This procedure uses controlled electrical energy to restore a normal heart rhythm. Cardioversion works for many patients, but the irregular rhythm often comes back because of that, doctors are always looking for ways to reduce the risk of another episode.

This new trial enrolled 200 adults with persistent atrial fibrillation. These adults came from five hospitals in the United States, Canada, and Australia. Every person in the study had a history of drinking coffee either currently or in the past five years. All patients were scheduled to undergo cardioversion, and the researchers wanted to know what would happen if some continued drinking coffee and others stopped completely.

The study design was simple. Half of the patients were asked to drink at least 1 cup of caffeinated coffee daily for 6 months after their cardioversion. The other half were asked to avoid all coffee and all products that contain caffeine. This included decaffeinated coffee because decaffeinated products still contain a small amount of caffeine.

The main question the researchers wanted to answer was whether there would be a difference in the number of patients who had another episode of atrial fibrillation during the six-month follow-up period. The study was open-label. This means both the patients and the researchers knew which group each patient was in. The random assignment helped ensure the groups were similar so that any difference in outcomes could be linked to the coffee exposure.

The average age of the people in the study was sixty-nine years. About seventy-one percent of the participants were men. Before the trial began, the typical patient in each group drank about seven cups of coffee per week. During the study, the coffee group continued to drink an average of seven cups a week. The abstinence group drank almost no coffee.

Results of the AFib and Coffee Trial

The results were surprising to many people who still believe that caffeine is dangerous for people with abnormal heart rhythms. Forty-seven percent of the people in the coffee group had another episode of atrial fibrillation or atrial flutter. That number is high, but it is expected because atrial fibrillation often returns even with good treatment. However, sixty-four percent of the abstinence group had another episode. This means the patients who drank coffee had a lower risk of having the rhythm problem return.

The researchers used a measurement called a hazard ratio to compare the two groups. A hazard ratio of one point zero would mean there is no difference. In this study, the hazard ratio was 0.61. This means the coffee group had a thirty-nine percent lower risk of a repeat episode than the group that did not drink coffee. The difference was strong enough that it was very unlikely to be due to chance.

There was another result that is important for patients and doctors. There was no difference in serious side effects between the two groups. This means that drinking coffee did not cause harm in this specific population of patients. There were no signals that coffee triggered dangerous events or led to worse outcomes.

This result challenges a long-standing belief. Many people assumed that caffeine would make atrial fibrillation more likely. The idea was based mostly on older theories and not on solid clinical data. Earlier observational research often found a neutral effect or even a small protective effect from coffee. However, observational research can be influenced by outside factors. That is why a randomized trial is important. A randomized trial is the strongest way to test cause and effect in medicine.

Coffee May Reduce the Risk of AFib Episodes

The results of this trial suggest that moderate consumption of caffeinated coffee may be safe for patients who have atrial fibrillation and who have recently undergone cardioversion. In fact, the results suggest that coffee may reduce the risk of having another episode. The study does not fully explain why this happens. There are several possible reasons.

Coffee beans contain many natural compounds beyond caffeine. Some of these compounds may reduce inflammation. Some may improve blood vessel function. Some may affect how electrical signals travel through the heart muscle. These effects might help protect the heart from irregular rhythms. It is also possible that regular coffee drinkers in the study had better health behaviors or routines that supported heart health. The randomized design helps limit this type of bias, but it cannot remove every possible factor.

The amount of coffee in the study is also important. The patients were encouraged to drink at least one cup of coffee a day. They did not drink extremely high amounts. Very high caffeine intake can cause problems such as anxiety and trouble sleeping. It can also lead to temporary increases in heart rate. The study did not test very high levels of caffeine intake. Therefore, the results apply only to moderate coffee intake.

The study also did not include people who have never consumed coffee. The results only apply to people who already drink coffee and have a history of tolerating it. Patients who feel unwell after drinking coffee or who have other medical issues may not respond the same way.

Doctors may need to rethink old advice about caffeine. Telling all patients with atrial fibrillation to avoid coffee may not be helpful, and in some cases, it may take away a drink that brings comfort and routine to their day. People often enjoy the taste and social experience of coffee. Removing it without strong evidence can reduce quality of life.

More Research is Needed

This trial is one piece of evidence. More research will be needed to understand how coffee affects different types of heart rhythm disorders. It is possible that the benefit seen in this group would not apply to other cardiac conditions. It will be important to study patients with very high caffeine intake and patients with severe structural heart disease. It will also be important to understand how other caffeinated products, such as tea or energy drinks, compare to regular coffee.

For now, the results of this study offer reassurance. Patients who enjoy coffee may be able to continue drinking it after cardioversion. They should always talk with their cardiologist because each patient is different. This study gives patients and clinicians useful evidence to guide those conversations.

For the pharmaceutical and medical community, this trial also reminds us why randomized research remains essential. Many assumptions in medicine come from a long tradition or theories that were never tested. When a question is tested directly, sometimes the answer surprises us. That is what happened here.

The key message is simple. For patients with atrial fibrillation who have undergone cardioversion and who already drink coffee, moderate caffeinated coffee intake may reduce the risk of another episode. It also appears to be safe in this context. This allows clinicians to give more balanced advice and to reduce unnecessary restrictions on patients' lives.

Coffee has always been more than a drink. It is part of daily rituals, cultures, and routines. For many patients, it brings comfort during stressful periods of illness. It is helpful to know that for many people with atrial fibrillation, one cup a day may be both safe and possibly even helpful.

Does your organization operate on long-standing assumptions that haven't been rigorously tested? At Metis Consulting Services, we specialize in evidence-based strategy, helping you move beyond conventional wisdom Contact us today to ensure your decisions are grounded in the strongest current evidence. hello@metisconsultingservices.com .

Sources

1. Clinical Trial Registration NCT05121519 https://www.clinicaltrials.gov/study/NCT05121519 

2. Journal article summary from JAMA Network: https://jamanetwork.com/journals/jama/fullarticle/2822040