What’s more, the study also found that drinking coffee may actually help protect the heart against arrhythmias.
The study used information gathered by the UK Biobank—a large prospective study of participants in England’s National Health Services. The researchers evaluated data from more than 386,000 coffee drinkers who were taking part in the study.
After adjusting for other lifestyle factors, the researchers considered how the participants’ coffee intake might be associated with their heart-related health outcomes.
The main finding of the study was that there was no link between daily coffee consumption and a rapid or uneven heartbeat. However, the researchers also noted that having an additional eight-ounce cup of coffee per day was actually associated with a 3% reduced risk of developing a problem with heart rhythm.
“We found no evidence that caffeine consumption leads to a greater risk of arrhythmias,” Gregory Marcus, MD, a cardiologist and a professor of medicine at the University of California, San Francisco, School of Medicine, and the lead author of the study, tells Verywell.
A Look at Genetic Factors
In addition to looking for any relationship between coffee intake and arrhythmias, the study also evaluated the participants for genetic factors that affect how caffeine is metabolized.
The researchers used a technique called Mendelian randomization when they reviewed the participants’ genetic data to help them determine if there could be a genetic basis for any relationship between caffeine and arrhythmias.
“We were unable to identify any interactions between various genes that play a role in caffeine metabolism and the possible coffee-arrhythmia relationship,” says Marcus. “However, there may yet be other genes or perhaps other environmental influences that render some rare individuals prone to more arrhythmia symptoms when they consume coffee.”
Marcus adds that some people do seem to “experience more symptoms of arrhythmias when they consume coffee or caffeine” but that these individuals “are the more rare exception rather than the rule.”
Coffee Could Be Protective
Marcus says that while studies have suggested that drinking coffee did not cause heart arrhythmias, the research has also been contradictory. “A protective relationship has been described in regard to atrial fibrillation before,” he says. “But no previous study has demonstrated a reduced risk of all arrhythmias among coffee consumers.”
The researchers also relied on participants reporting how much coffee they drank. Those responses could have been variable as people may have reported their intake inaccurately. While the UK Biobank did ask participants about how much tea they drank, Marcus’ research did not evaluate other sources of caffeine such as tea or cola.
It’s also worth noting that the study Marcus led looked at whether coffee affected arrhythmias—not specifically caffeine, a well-known and well-loved stimulant that can be consumed in forms other than coffee.
“There are several biologically plausible mechanisms that could explain a protective effect of either coffee or caffeine on arrhythmias,” says Marcus. He points out that there are other ingredients in coffee besides caffeine, and some might explain why coffee appears to have a protective role against arrhythmias.
An 8-ounce cup of regular coffee can have about 80 milligrams (mg) to 100mg of caffeine. An 8-ounce cup of black or green tea has about 30mg to 50mg of caffeine. A 12-ounce serving of most colas (an average soda can) has about 30mg to 40mg of caffeine. Energy drinks can have as little as 8mg and upwards of 250mg of caffeine per fluid ounce.
For example, caffeine has an adrenaline-like effect that might suppress some arrhythmias. It could also be that the stimulating effect helps motivate people to exercise more, which in turn helps their hearts.
Future Research
Marcus and his colleagues are continuing to investigate coffee drinking and heart rhythms and there is a need for more robust research.
“We recently completed a study where the same individuals were randomly assigned to consume versus avoid coffee while wearing a continuous electrocardiogram recording device. We are analyzing those results now,” says Marcus. “However, we would love to perform a large trial should funding support from an unbiased source become available.”
Such a clinical trial—where participants are divided into groups who drink coffee or those who do not—would help researchers understand if there is evidence to support advising people about their coffee drinking habits and heart health.
In fact, some people may get heart-protective benefits, as drinking coffee was associated with a lower risk of arrhythmias.
