Doctors have always told patients with atrial fibrillation (AF) to limit caffeine, saying it could trigger irregular heartbeats, however, a new international trial shows that moderate coffee intake is safe, and could lower the risk of AF returning after treatment.

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AF is the most common heart rhythm disorder, also known as arrhythmia, where there is very fast and disorganised contraction of the top chambers of the heart.

Published in JAMA on November 9, the DECAF trial (Does Eliminating Coffee Avoid Fibrillation?) enrolled 200 adults across five hospitals in the United States, Canada, and Australia.

All participants were either current or recent coffee drinkers with persistent AF or atrial flutter who were scheduled for electrical cardioversion, a procedure that restores normal heart rhythm.

After successful cardioversion, participants were randomly assigned to two groups; one continued to drink at least one cup of caffeinated coffee daily, while the other completely refrained from coffee and other caffeine-containing products for six months.

Baseline coffee consumption was similar in both groups, averaging about seven cups per week.

By the end of the study, among those who continued drinking coffee, 47 percent experienced a recurrence of AF or atrial flutter. In contrast, 64 percent of those in the caffeine-abstinence group had a recurrence.

Drinking coffee was associated with a 39 percent lower hazard of recurrent AF compared with refraining. When focusing only on AF episodes, the benefit was comparable. There were no differences in adverse events such as hospitalizations, strokes, or heart attacks between the groups.

Dr. Gregory Marcus, a cardiologist and senior author from the University of California, San Francisco, said the findings challenge long-held beliefs that coffee is harmful for people with AF, suggesting that moderate coffee consumption could even help protect against arrhythmia recurrence.

The trial is among the first randomized clinical tests to examine coffee’s effects in people with AF. While earlier observational studies suggested that coffee might have a neutral or even beneficial impact on heart rhythm, they couldn’t account for lifestyle or other contributing factors.

According to researchers, by using randomization, the DECAF trial helped level those differences, and offered stronger evidence for its findings.

Researchers suggest several explanations, noting that caffeine’s ability to block adenosine receptors may help prevent the triggers that lead to atrial fibrillation. Coffee’s anti-inflammatory properties could also help, since inflammation is a known risk factor for AF.

Additionally, coffee drinkers often tend to be more physically active, and the beverage’s hydrating effect may help reduce the risk of irregular heart rhythms.

The study had some limitations, including its open-label design, where participants knew whether they were consuming coffee or not. Researchers also did not follow a strict schedule for arrhythmia monitoring, and some eligible patients declined to participate, either because they didn’t want to give up coffee or weren’t willing to increase their intake.

Even after accounting for small differences among participants, the findings remained consistent. The researchers caution, however, that people’s reactions to caffeine can vary, and those who are sensitive were likely underrepresented in the study.

For clinicians and patients in coffee-loving regions such as Rwanda, the study provides evidence that cutting out coffee may not be necessary for most people with persistent AF. Though personal triggers and other health conditions must always be considered, a cup of coffee each day can likely be enjoyed without increasing risk of recurrent arrhythmia.