In a new study from the University of California, San Francisco, researchers found caffeinated coffee may come with a blend of short-term benefits and harms.
They closely monitored 100 volunteers for two weeks and found participants logged more steps a day on days when they drank coffee than on days when they didn’t.
And more coffee was associated with fewer episodes of one type of abnormal heart rhythm.
But on days they drank coffee, participants had more incidents of another type of abnormal heartbeat. They also slept less.
In the study, volunteers wore continuous recording monitors to track heart rhythm and blood sugar levels. Wrist-worn devices tracked physical activity and sleep.
Over two weeks, they were assigned to either avoid or drink coffee for no more than two consecutive days each. Coffee and espresso consumption was tracked in real-time via a “timestamp button” on the heart monitor.
The team found compared to days when participants did not drink coffee, coffee consumption was linked to more than 1,000 additional steps per day, 36 fewer minutes of sleep per night, and a 54% increase in episodes of a type of abnormal heartbeat that originates in the lower heart chambers, called premature ventricular contractions.
More frequent abnormal beats from the lower chambers increase the risk of heart failure.
Each additional cup of coffee was associated with nearly 600 more steps per day and 18 fewer minutes of sleep a night.
But episodes of an abnormally rapid heart rhythm that arise from the upper heart chambers, called supraventricular tachycardia, were 12% less frequent for each additional cup.
Researchers also found people with genes associated with faster caffeine metabolism exhibited more abnormal heartbeats originating in the lower chambers of the heart when more coffee was consumed.
The slower a coffee drinker metabolized caffeine, the more sleep they lost.
The team says that because coffee was randomly assigned to the study participants – with repeated assessments of days when each participant drank coffee versus days when they did not – cause-and-effect can be inferred.
The study is presented at the American Heart Association’s virtual Scientific Sessions. One author of the study is Dr. Gregory Marcus.
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