According to the researchers, there is a perception that caffeine can be a trigger for heart rhythm problems, but this study suggests that drinking up to three cups of coffee a day may be safe for people with arrhythmia and may even have protective effects.
Arrhythmia, or abnormal heart rhythms, involves the heart beating too quickly, slowly, or unevenly. While in some cases, arrhythmia may be harmless or even go unnoticed, in others, the risk of sudden cardiac arrest can increase.
Atrial fibrillation (AFib), the most common heart rhythm disorder, causes the heart to beat rapidly and skip beats, and if left untreated, can lead to strokes.
A single cup of coffee contains about 95mg of caffeine and acts as a stimulant to the central nervous system. Once in the body, caffeine blocks the effects of adenosine, a chemical that can facilitate AFib.
Therefore, the authors analysed multiple population-based studies to determine an association between caffeine intake and its effects on atrial and ventricular arrhythmia (VA).
These studies have consistently shown a decrease in AFib with an increase in caffeine ingestion, with one meta-analysis of 228,465 participants showing AFib frequency decreasing by 6% in regular coffee drinkers, and a further analysis of 115,993 patients showing a 13% risk reduction.
"There is a public perception, often based on anecdotal experience, that caffeine is a common acute trigger for heart rhythm problems," said the review's lead author, Dr Peter Kistler, director of electrophysiology at Alfred Hospital and Baker Heart and Diabetes Institute in Australia. "Our extensive review of the medical literature suggests this is not the case."
The authors also determined that caffeine has no effect on VA — caffeine doses of up to 500mg daily (equivalent to six cups of coffee) did not increase the severity or rate of VA.
A randomised study of 103 post-heart attack patients who received an average of 353 mg/day resulted in improved heart rate and no significant arrhythmia. Only two studies showed an increased risk for VAs, where patients ingested at least 10 cups and nine cups a day, respectively.
"Caffeinated beverages such as coffee and tea may have long term anti-arrhythmic properties mediated by antioxidant effects and antagonism of adenosine," Kistler said.
"In numerous population-based studies, patients who regularly consume coffee and tea at moderate levels have a lower lifetime risk of developing heart rhythm problems, and possibly, improved survival."
However, the authors determined that energy drinks should be avoided by patients with pre-existing heart conditions. One energy drink can contain anywhere from 160 to 500mg of concentrated caffeine, and 75% of patients with pre-existing heart conditions who consumed two or more energy drinks a day reported palpitations within 24 hours.
The research concluded that both large population studies and randomised control trials suggest caffeine intake of up to 300mg a day may be safe for arrhythmia patients.
"Although there is no clearly defined threshold for caffeine harm, a regular intake of up to 300mg/day appears to be safe and may even be protective against heart rhythm disorders," it stated.
But it cautioned that there may be individual differences in susceptibility to the effects of caffeine, and that this issue requires further research.
Source: JACC: Clinical Electrophysiology
VOL. 4, NO. 4, 2018
"Caffeine and Arrhythmias Time to Grind the Data"
Authors: Peter Kistler, et al.