Skip to main content

New Evidence on How Alcohol and Caffeine Affect Heart Rhythm Found in UCSF Studies

In separate studies, UC San Francisco researchers examined the effects of two widely consumed beverages – coffee and alcohol – on irregular heartbeat.


Study 1: Coffee Consumption and Incident Tachyarrhythmias

  • UCSF scientists investigated whether regular coffee consumption was associated with arrythmias and whether genetic differences in caffeine metabolism affected the association.
  • During follow-up, just 4 percent of participants developed an arrythmia.
  • There was no evidence that regular coffee consumption or genetic differences in caffeine metabolism increased cardiacarrythmia risk.

Caffeinated coffee has been associated with a lower risk of cancer, diabetes, Parkinson’s disease and overall mortality. Without much evidence, it is also assumed to heighten the chance of arrythmias. UCSF cardiologist and electrophysiologist Gregory Marcus, MD, and a team of researchers set out to test this assumption. In the largest prospective cohort study of its kind, they utilized data from more than 380,000 participants aged 40 to 69 from a large databank of health and genetic information in the U.K. Participants, slightly more women than men, were grouped into eight categories based on how much coffee they drank, with a median of two cups a day. They were also genotyped for variations in caffeine metabolism.


Mendelian randomization

Most research supporting an association between caffeine and arrhythmias is observational and relies on self-reports about the amount of coffee consumed. In addition to self-reports, USCF scientists used Mendelian randomization analysis to identify alleles in common genetic variants associated with coffee consumption. Since no other factors can affect the genotype, this helped mitigate the confounding common in observational, self-report studies.


No evidence of caffeine-arrythmia relationship

During a four-year follow-up, there were 16,369 incident arrhythmias of all types, including supraventricular and ventricular tachycardias and premature atrial and ventricular complexes. More coffee consumption was associated with a lower risk of all arrhythmias grouped together. Only lower risks of atrial fibrillation (AF) alone and supraventricular tachycardia alone reached statistical significance when each arrhythmia type was examined together. There was no evidence of a greater arrhythmia risk among slow or fast metabolizers.

 The researchers suggest several possible explanations for this finding. One may be caffeine’s antioxidant and anti-inflammatory properties. Inflammation is an underlying mechanism in cardiac arrythmias and, as evidence increasingly suggests, atherosclerosis. Caffeine also blocks adenosine receptors. High adenosine is known to trigger AF and its inhibition is associated with reduced AF in animal models. Further, caffeine seems to increase left atrial effective refractory periods while AF occurs more readily when atrial refractory periods are short.


Caffeine is safe and possibly protective

The study is notable for its unprecedented sample size and Mendelian randomization analysis. “Only a randomized clinical trial can definitely demonstrate the clear effects of coffee and caffeine,” Marcus said. “But our study found no evidence that consuming caffeinated beverages increased the risk of arrythmia. It provides reassurance that common prohibitions against caffeine to reduce arrhythmia risk are likely unwarranted.” He added that coffee may even protect against some arrhythmias.


Study 2: Acute Consumption of Alcohol and Discrete Atrial Fibrillation Events

  • Long-term alcohol use is associated with atrial fibrillation (AF), the most common arrhythmia affecting some 12 million people in the United States.
  • Patients with AF also cite alcohol as an acute trigger.
  • Marcus and a team of UCSF researchers investigated the association between drinking alcohol and an AF episode occurring a few hours later.
  • Alcohol may be a modifiable risk factor for recent AF events in patients with arrhythmia. 

 Long-term alcohol use is associated with atrial remodeling, making the atria more prone to fibrillate. Yet patients with AF also report AF episodes within hours of drinking. To test the validity of these reports, researchers recruited 100 adults with paroxysmal AF from UCSF cardiology and electrophysiology clinics. 


Real-time monitoring

For a median 27 days, participants wore an electrocardiogram (ECG) monitor that recorded the time and duration of each AF episode lasting more than 30 seconds. They were asked to press a button on the monitor every time they had a standard glass of wine, 12 ounces of beer or a shot of liquor. This provided real-time self-reporting of drinking events; a transdermal ankle sensor provided passive alcohol monitoring. Participants also had in-person visits at two and four weeks, where they were tested for phosphatidylethanol (PEth), an established marker of alcohol consumption reflecting alcohol consumed in the past two to three weeks.


One drink doubles the chance of acute AF events

More than half of study participants – 56 percent – had at least one episode of AF. One drink was associated with a twofold risk of a discrete AF event within a few hours and two drinks with a threefold risk. Both the total amount of alcohol and peak alcohol concentration detected by the wearable sensor also predicted a heightened risk of AF within hours.

“These observations mirror what have been reported by patients for decades,” Marcus, the study’s senior author, said. “But this is the first measurable, objective evidence that a modifiable exposure may acutely influence the chance that an AF episode will occur.”


To learn more

UCSF Cardiac Electrophysiology and Arrhythmia Service

Phone: (415) 353-2554 | Fax: (415) 353-2528

Refer a patient

Clinical trials