Contrary to conventional wisdom, a coffee a day may help keep arrhythmia away, or at least it likely won’t increase risk, a new study has shown.

Published in JAMA Internal Medicine, the study reviewed the association between coffee consumption and arrhythmia risk in 368,258 UK Biobank participants between 2006 and 2018.

It found that each additional cup of habitual coffee consumed was associated with a 3% reduced risk of incident arrhythmia (HR: 0.97, 95% CI: 0.96–0.98, P < 0.001), after adjusting for demographic characteristics, comorbid conditions and lifestyle habits.

The risk of atrial fibrillation and/or flutter (AF) (HR: 0.97, 95% CI: 0.96-0.98, P < 0.001) and supraventricular tachycardia (HR: 0.96, 95% CI: 0.94–0.99, P = 0.002) risks were similarly lowered with habitual coffee consumption.

These associations were not significantly modified by genetic variants that affect caffeine metabolism, the authors wrote.

They said the findings were consistent with previous studies that showed reduced risk of or no association with AF.

If caffeine does affect arrhythmia risk, it may do so by prolonging left atrial effective refractory periods, blocking adenosine receptors and acting as an anti-inflammatory, the authors proposed.

“Even the catecholaminergic properties of caffeine could be protective against some arrhythmias, such as some premature ventricular complexes, as well as some arrhythmias triggered by enhanced vagal tone,” suggested Dr Eun-jong Kim of the Division of Cardiology, University of California, San Francisco.

AF is associated with shorter atrial effective refractory periods, higher doses of adenosine and can be triggered by inflammation, he noted.

However, while the authors’ results “strengthen the evidence that caffeine is not pro-arrhythmic … they should not be taken as proving that coffee is anti-arrhythmic”, cardiologist, Associate Professor Zachary Goldberger and internal medicine specialist, Professor Rodney Hayward warned in an accompanying commentary.

Additionally, the study cohort only included patients who did not have a formal prior arrhythmia diagnosis, and it is unclear whether coffee could aggravate atrial or ventricular ectopy, they wrote.

“The current study suggests that we can tell patients that waking up to a cup of coffee is not a dangerous ritual,” they said

“However, it will be more important to listen to patients about their symptoms in association with coffee or caffeine exposure and engage in shared decision-making on an individual level.”