In a groundbreaking, extensive study, researchers have revealed the potential health effects of caffeine, providing unprecedented insights into the impacts of coffee consumption.
The investigation, conducted by a team of international researchers, has been presented at the American Heart Association’s Scientific Sessions 2021, illuminating the short-term health effects of caffeine, both beneficial and detrimental. The researchers ascertained that caffeinated coffee causes increased abnormal heartbeats, increased physical activity, and reduced sleep duration.
The study was funded by a UCSF Cardiology Innovation Award, the Naify Center for Atrial Fibrillation Research, and the University of California, San Francisco Division of Cardiology.
Gregory Marcus, the study’s author, associate chief of cardiology for research and endowed professor of atrial fibrillation research at the University of California, San Francisco, said: “Coffee is the most commonly consumed beverage in the world, yet its health effects remain uncertain.
“While the majority of long-term observational studies have suggested multiple potential benefits of drinking coffee, this is the first randomised trial to investigate the real-time, physiologic consequences of coffee consumption.”
Measuring coffee consumption
To investigate the effects of caffeine in coffee, the researchers studied100 participants who continuously wore ECG devices to measure heart rhythm, wrist-worn devices to track physical activity and sleep, and glucose monitors to analyse blood sugar levels for two weeks. The individuals had an average age of 38 years, 51% were women, and 48% were white. In addition, the researchers acquired DNA saliva samples from each of the participants to assess genetic variants that may influence caffeine metabolism.
Next, the individuals were randomly assigned to either consume or avoid coffee for no more than two consecutive days each for the study period of two weeks. A timestamp button on the ECG monitor was employed to record coffee and espresso consumption in real-time, with trips to coffee shops logged through geo-tracking. The participants also completed questionnaires each day to log how much coffee they consumed each morning.
Revealing the effects of caffeine in coffee
Surprisingly, the researchers discovered that the effects of caffeine on short-term health are rather diverse. Firstly, they found that coffee consumption was associated with a 54% increase in premature ventricular contraction – an abnormal heartbeat originating in the lower heart chambers that feels like a skipped heartbeat. Contrastingly, increased coffee consumption was associated with fewer experiences of supraventricular tachycardia – an abnormally fast heart rhythm deriving from the upper heart chambers.
Perhaps unsurprisingly, the effects of caffeine were found to increase physical activity and reduce sleep. There were over 1,000 additional steps logged per day in the group that consumed coffee compared to those that did not, with each additional coffee equating to 600 extra steps per day.
Drinking in excess of one coffee was found to double the number of irregular heartbeats in the low chambers. The participants who drank coffee slept 36 fewer minutes per night than those who did not– each additional cup leading to 18 fewer minutes of sleep each night.
Marcus said: “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.
“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 individuals who had genetic variants linked to faster caffeine metabolism displayed more abnormal heartbeats in the ventricles when they drank more coffee. Furthermore, the slower an individual metabolised caffeine based on their genetics correlated to more sleep lost when they consumed caffeinated coffee.
The team also investigated if changes in sleep or exercise altered the effects of caffeine on abnormal heart rhythms, for which no association was identified.
