Drinking coffee may have concerning effects on heart rhythm and sleep, according to a new study presented at the 2021 Scientific Sessions of the American Heart Association and described in an article at HealthDay.
Drinking coffee is linked to a number of potential health benefits, from improved insulin sensitivity to lower risks for heart failure and liver disease. And as we noted recently, drinking coffee — as well as tea — is linked to a lower risk for both dementia and stroke. But certain risks associated with coffee have also been known for a while, including increased risks for high cholesterol and dementia linked to heavy coffee drinking.
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For the latest study, researchers at the University of California, San Francisco, and Duke University were interested in exploring the effects of drinking coffee on heart function. They recruited 100 regular coffee drinkers as participants, with an average age of about 38 and an average body-mass index (BMI, a measure of weight in relation to height) that fell in the normal range (not overweight or obese). Participants wore several health-tracking devices as part of the study — a Fitbit (which records physical activity), a heart monitor, and a continuous glucose monitoring (CGM) device. Over a two-week period, participants were randomly assigned on a daily basis either to drink as much coffee as they desired, or not to drink coffee that day. This gave the researchers data they could use to compare the effects of drinking, or not drinking, coffee — both over time in individual participants, and between different participants.
The researchers found no evidence that drinking coffee increased the risk for arrhythmias (irregular heartbeats) in the upper chambers of the heart, or atria — an important finding since atrial fibrillation, also known as Afib, is a potentially dangerous condition that causes the risk for blood clots and stroke, among other possible complications. But they did find that coffee increased the risk that the lower chambers of the heart, or ventricles, had arrhythmias. In particular, participants were about 50% more likely to experience premature ventricular contractions (PVCs) — essentially extra heartbeats — on days when they drank coffee. While PVCs happen to nearly everyone on occasion and are usually not considered harmful, some studies have shown that having a higher number of PVCs increases the long-term risk for heart failure (inability of the heart to pump enough blood).
Another effect seen on days when participants drank coffee was less sleep, with participants sleeping about a half-hour on average less after one of these days. For each cup of coffee that participants drank, they slept an average of about 18 minutes less that night. This effect wasn’t seen in all participants, though — those who had a genetic variant linked to faster metabolization of caffeine experienced no significant sleep reduction on days when they drank coffee. And on the positive side, participants were more active on days when they drank coffee, taking an average of about 1,000 steps more than on days when they didn’t drink coffee. Each cup of coffee consumed was linked to an increase of about 500 steps that day.
This study, like any single study, doesn’t definitively show any link between drinking coffee and health risks. But it does suggest that if you’re experiencing certain health problems — like trouble sleeping — you might want to reconsider the role of coffee in your everyday life. It’s also worth noting that since the study included only regular coffee drinkers as participants, it didn’t demonstrate any differences between regularly consuming coffee over time and completely abstaining from coffee over time. It’s possible that a study comparing these two behaviors would lead to different results.
Want to learn more about protecting your heart? Read “Be Heart Smart: Know Your Numbers,” “Does Diabetes Hurt Your Heart?” “Fight Off Heart Disease With These Five Heart-Healthy Foods” and “Lower Your Risk of Heart Disease.”