Coffee Consumption Has Both Beneficial and Harmful Short-Term Health Effects, Says New Study

by johnsmith

In a new randomized trial, participants who drunk caffeinated coffee for two weeks were more physically active, yet they also had an increased number of abnormal heartbeats and slept less.

Marcus et al. found that coffee consumption increases ventricular ectopy, increase physical activity, and reduces sleep duration. Image credit:

Marcus et al. found that coffee consumption increases ventricular ectopy, increase physical activity, and reduces sleep duration. Image credit:

“Coffee is the most commonly consumed beverage in the world, but its health effects remain uncertain,” said Professor Gregory Marcus, a researcher in the School of Medicine at the University of California, San Francisco.

“The majority of coffee-related research has been observational (prone to confounding) and examined long-term effects less relevant to immediate consequences.”

“We sought to perform randomized trials within individuals to capture real-time physiologic consequences of coffee consumption.”

The study involved 100 adult volunteers (mean age – 38 years, 51% women, 48% non-Hispanic white).

They were then randomly assigned to either avoid or consume coffee for no more than two consecutive days each for 14 consecutive days.

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 14 days.

The researchers also obtained DNA saliva samples from the participants to assess genetic variants that may affect caffeine metabolism.

Coffee and espresso consumption were recorded in real time via a ‘time stamp button’ on the ECG monitor, and the authors tracked trips to coffee shops with geotracking.

In addition, participants completed daily questionnaires to detail how much coffee they had consumed every morning.

The team 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.

Consuming coffee was consistently associated with more physical activity as well as less sleep.

“More physical activity, which appears to be prompted by coffee consumption, has numerous health benefits, such as reduced risks of Type 2 diabetes and several cancers, and is associated with greater longevity,” Professor Marcus said.

“On the other hand, reduced sleep is associated with a variety of adverse psychiatric, neurologic and cardiovascular outcomes.”

“More frequent abnormal heartbeats from the upper heart chambers influence risk of atrial fibrillation, and more frequent abnormal beats from the lower chambers, or ventricles, increase the risk of heart failure.”

“These results highlight the complex relationship between coffee and health.”

The study participants with genetic variants associated with faster caffeine metabolism exhibited more abnormal heart beats originating in the ventricles when more caffeinated coffee was consumed.

The slower an individual metabolized caffeine based on their genetics, the more sleep they lost when they drank caffeinated coffee.

The scientists also sought to determine if changes in exercise or sleep influenced coffee’s effects on abnormal heart rhythms, and no such association was identified.

“Because coffee was randomly assigned to the study participants, cause-and-effect can be inferred,” Professor Marcus said.

“These observations were made during repeated assessments of days when coffee was consumed versus when it was not for each study participant, eliminating concerns regarding differences in individual-level characteristics as an explanation for these results.”

The researchers presented their findings this week at the American Heart Association’s Scientific Sessions 2021.


Gregory M. Marcus et al. The Coffee and Real-Time Atrial and Ventricular Ectopy (CRAVE) Trial. AHA2021

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