Cup of black coffee with beans on wooden table

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DALLAS, Texas — Coffee is the most popular drink around the globe. Although many studies have found that caffeinated coffee can be a healthy part of a balanced diet and provide boosts in both energy and alertness, a new report finds that morning cup of java can have a number of harmful short-term health effects too. Researchers with the American Heart Association say, along with increasing physical activity, drinking coffee also reduces the amount of sleep people get and increases the chance of experiencing abnormal heartbeats.

Coffee is the most commonly consumed beverage in the world, yet its health effects remain uncertain,” says study author Gregory Marcus, M.D., M.A.S., from the University of California-San Francisco in a media release. “While the majority of long-term observational studies have suggested multiple potential benefits of drinking coffee, this is the first randomized trial to investigate the real-time, physiologic consequences of coffee consumption.”

Researchers gathered 100 adults who they tracked using continuously recording ECG devices to monitor heart rhythm while drinking caffeinated coffee. The volunteers also wore wrist devices to track physical activity levels and the sleep duration. Continuous glucose monitors kept track of each person’s blood sugar levels over the two-week experiment. Researchers also took DNA saliva samples from each person to see if the impact of drinking coffee depends on a person’s ability to metabolize caffeine.

Over 14 days, the team randomly assigned each participant to either avoid or consume coffee for two straight days before switching tasks. Researchers were able to track the exact times the volunteers drank coffee through a “time stamp button” on the ECG monitor and a GPS tracker which monitored when they entered coffee shops. Each person also filled out a questionnaire, revealing how much coffee they drink in the morning and throughout the day.

READ MORE: 7 Health Benefits From Drinking Coffee Every Day, According To Scientists – Study Finds

The good and bad of drinking coffee

The results of the two-week experiment show that drinking coffee leads to a 54-percent increase in premature ventricular contractions. This is a type of irregular heartbeat that takes place in the lower heart chambers. People who experience this report feeling like their heart skipped a beat. On the other hand, people drinking more coffee reported having fewer episodes of supraventricular tachycardia, which is a rapid heart rhythm in the upper heart chambers.

Another positive of coffee, study authors find the daily caffeine boost leads to more physical activity. Coffee drinkers logged over 1,000 extra steps each day in comparison to the days they avoided coffee. For each additional cup of coffee they drank, participants took nearly 600 extra steps during the day.

Unfortunately, the caffeine boost negatively impacted the time people spent sleeping. On average, the volunteers got 36 fewer minutes of sleep after consuming caffeinated coffee, according to their Fitbit devices. For every cup of coffee consumed, participants slept for 18 fewer minutes that night.

The study did not find any noticeable changes in blood sugar levels on days when the group avoided or consumed coffee.

“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,” Marcus reports. “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.”

Do coffee benefits depend on your genes?

Using the DNA samples, the team found that coffee drinkers with genetic variants that create a faster caffeine metabolism experienced more irregular heartbeats. Conversely, the slower someone’s genes metabolized caffeine led to those individuals losing more sleep after drinking coffee.

Dr. Marcus notes that, although this was an observational study, scientists can see a clear cause-and-effect from drinking coffee since the team randomly assigned the coffee drinking tasks to participants.

Researchers presented their findings at the American Heart Association’s Scientific Sessions 2021.

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About Chris Melore

Chris Melore has been a writer, researcher, editor, and producer in the New York-area since 2006. He won a local Emmy award for his work in sports television in 2011.

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