Why Coffee Causes Some Healthy People’s Hearts to Skip Beats

Introduction

This review examines a study from the University of California, San Francisco, investigating the negative effects of coffee consumption on heart health and sleep.

Heart Skips Beats

The study indicates that while coffee can serve as a quick pick-me-up, it also has mixed effects on health. Researchers found that coffee helps people stay active but significantly deprives some of sleep. While coffee consumption does not cause irregular rhythms in the heart’s upper chambers, it can cause the lower chambers to skip beats. These findings were presented at the online annual meeting of the American Heart Association.

Lead author Dr. Gregory Marcus, associate Chief of Cardiology for research at the University of California, San Francisco, said, “People should understand that this extremely commonly consumed beverage really does have substantive effects on our health, and they’re variable. It’s not that coffee is necessarily all good or all bad. It’s very likely that whether it’s net good or net bad depends on a combination of factors.”

Dr. Sana Al-Khatib, a heart rhythm expert with the Duke Electrophysiology Clinic in North Carolina, who was not involved with the study, added, “A very common question we get almost every week from patients is: Can I drink coffee? Especially in patients with atrial fibrillation.” She noted that previous studies had mixed results, making it difficult for clinicians to advise patients.

The Trial

For this clinical trial, Dr. Marcus and his team recruited 100 coffee drinkers and fitted them with devices such as a Fitbit, a heart monitor, and a blood glucose tracker. Over two weeks, participants were randomly assigned daily to either drink as much coffee as they liked or to abstain. The researchers then tracked health changes in each person based on their coffee consumption.

The Findings

The study found no evidence that coffee consumption caused irregular rhythms in the atria, the heart’s upper chambers. This is good news, as one major concern about coffee is its potential to promote atrial fibrillation. However, coffee consumption was found to cause the heart’s lower chambers, the ventricles, to skip beats.

Dr. Marcus said, “On days randomly assigned to coffee, people exhibited about 50% more Premature Ventricular Contractions [PVCs] — more early beats arising from the lower chambers of the heart. Those who consumed more than one drink of coffee exhibited essentially a doubling of their PVC counts.” He added, “These PVCs are common and are usually regarded as harmless. We all have them once in a while, and generally, they’re considered benign. But we and others have shown that more PVCs are an independent risk factor for heart failure over time. Not everyone with more PVCs has heart failure, but it is a factor.”

Other Factors

Coffee also significantly affected physical activity and sleep. Dr. Marcus said, “On days they were randomly assigned to drink coffee, participants on average took about 1,000 more steps than they normally would. For every additional cup of coffee consumed, there were an additional 500 steps.”

Sleep

Conversely, coffee tended to reduce sleep. Dr. Marcus stated, “On days randomly assigned to coffee, people slept on average about a half-hour less that evening. For every additional cup of coffee, there was about 18 minutes less sleep.”

However, people who were genetically inclined to metabolize coffee more quickly did not show a significant relationship between their coffee consumption and sleep deprivation.

Dr. Sana Al-Khatib noted that the study was well done, but she sees a need for follow-up research involving more patients over a longer time to determine if coffee’s immediate effects eventually lead to increased risks for heart disease, stroke, and other health problems.

The Cohort

Participants in this study were relatively young and healthy, with an average age of 38 and an average BMI on the high end of healthy. Dr. Al-Khatib commented that this is “Not typical of the patient population we see in clinical practice, who are older and have one or more health problems.”

Dr. Marcus stated, “If you’re concerned about the effects of coffee on your health, you should probably talk with your doctor. Depending on your personal health issues, it might make sense for you to either drink coffee or abstain from it.” He also said, “For those concerned about atrial fibrillation, these data suggest there’s no reason to worry about coffee consumption. On the other hand, if there are concerns about PVCs, it may make sense to avoid or minimize coffee consumption. If there’s a goal to increase or maintain physical activity, then coffee may be helpful. But for those who have difficulty sleeping, the sleep disruption caused by coffee may make it less worth it.”

The Way Ahead

Despite her reservations, Dr. Al-Khatib plans to use this study when counseling patients. She said, “I wouldn’t think of these results as, oh, OK, great, so what, let’s wait for the next study. I will incorporate those findings in my discussions with patients, of course, after I’ve read the full paper and assuming there are no surprises.”

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