The majority of long-term observational studies have suggested multiple potential benefits of drinking coffee, while this is the first randomized trial to investigate the real-time, physiologic consequences of coffee consumption.
Marcus and colleagues enrolled 100 adult volunteers, and they were assigned to wear continuously recording ECG devices (to track heart rhythm), wrist-worn devices to track physical activity and sleep; and continuous glucose monitors to track blood sugar levels for two weeks.
The participants were an average age of 38 years, 51% were women and 48% were white. Researchers also obtained DNA saliva samples from the participants to assess genetic variants that may affect caffeine metabolism.
Participants were then randomly assigned to either avoid or consume coffee for no more than two consecutive days each for 14 consecutive days.
Coffee and espresso consumption were recorded in real-time via an ECG monitor, and researchers tracked trips to coffee shops with geotracking. In addition, participants completed daily questionnaires to detail how much coffee they had consumed every morning.
The analysis found that coffee consumption was associated with a 54% increase in premature ventricular contractions, a type of abnormal heartbeat originating in the lower heart chambers reported to feel like a skipped heartbeat.
In contrast, drinking more coffee was associated with fewer episodes of supraventricular tachycardia, an abnormally rapid heart rhythm arising from the upper heart chambers.
The other findings were:
- Participants who consumed coffee logged more than 1,000 additional steps per day compared to days when they did not drink coffee.
- On the day’s participants drank coffee, they had 36 fewer minutes of sleep per night according to their Fitbit devices.
- Drinking more than one coffee drink more than doubled the number of irregular heartbeats arising from the heart’s lower chambers.
- Each additional cup of coffee consumed was associated with nearly 600 more steps per day and 18 fewer minutes of sleep per night.
- There were no differences in continuously recorded glucose measured when the study participants consumed versus avoided coffee.
These findings were corroborated by analyses of adherence to their randomization assignment and amplified when more versus less coffee was consumed.
Coffee consumption prompted more physical activity, has numerous health benefits, such as reduced risks of Type 2 diabetes and several cancers, and is associated with greater longevity.
On the other hand, reduced sleep is associated with a variety of adverse psychiatric, neurologic, and cardiovascular outcomes.
More frequent abnormal heartbeats influence the risk of atrial fibrillation, and heart failure. These results highlight the complex relationship between coffee and health.
The study participants with genetic variants associated exhibited more abnormal heartbeats when more caffeinated coffee was consumed because of faster metabolism.
The slower an individual metabolizes caffeine based on their genetics, the more sleep they lost when they drank caffeinated coffee.
Researchers also sought to determine if changes in exercise or sleep influenced coffee’s effects on abnormal heart rhythms, and no such association was identified.