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Disproven brew? Investigating the link between coffee and heart irregularities

Is too much coffee bad for the heart? a new study suggests not, and it is the biggest piece of fieldwork conducted to date.

Coffee Pods. — Photo: Andrés Nieto Porras (CC BY-SA 2.0)
Coffee Pods. — Photo: Andrés Nieto Porras (CC BY-SA 2.0)

Over the years there have been various medical reports that have indicated coffee may cause cardiac arrhythmia (an abnormality of the heart’s rhythm, causing the heart to beat too slowly, too quickly, or irregularly). A new study finds no evidence of this.

The previous research that indicates a problem primarily kinks cardiac rhythm disturbances to the toxic effects from very large doses of caffeine. This is based on caffeine administered in animal studies, with most of the research coming from the 1980s and 1990s.

The study, as Biotechniques reports, is the largest study ever undertaken into this issue. For this, researchers looked into the health statistics for 386,258 coffee drinkers, initially, and then four years later. While the focal point was caffeine as an active compound, the investigation was into coffee as this is the primary source of caffeine for the majority of the population (in the U.S. for example, 64 percent of the population regularly drink coffee each day).

With the recent findings, lead researcher Dr. Gregory Marcus, professor of medicine in the Division of Cardiology at UCSF, explains: “We found no evidence that caffeine consumption leads to a greater risk of arrhythmias. Our population-based study provides reassurance that common prohibitions against caffeine to reduce arrhythmia risk are likely unwarranted.”

To collect and analyse the data, the researchers used “Mendelian Randomization.” This, as the name suggests, involved using genetic data to infer any causal relationships. This was important because people who possess a genetic variant associated with faster caffeine metabolism can often drink more coffee than others.

Cup of coffee in a cafe. Image by Tim Sandle.

The method enabled researchers to test the caffeine-arrhythmia relationship in a way that did not rely on participant self-report. Through this, some of the weakness that affect observational studies were avoided.

As a further control measure, with a mean four-year follow up, data were adjusted for demographic characteristics, health and lifestyle habits.

With the 386,258 subjects, 4 percent developed an arrhythmia, which is classed as a weak relationship. Importantly, there was no evidence of a heightened risk of arrhythmias among those genetically predisposed to metabolize caffeine differently.

No study is without its limitations and here the researchers noted the self-reporting nature of the study, and that detailed information on the type of coffee – such as espresso or not – was unavailable.

The research was conducted at UC San Francisco. The findings appear in the journal JAMA Internal Medicine. The paper is titled “Coffee Consumption and Incident Tachyarrhythmias

Reported Behavior, Mendelian Randomization, and Their Interactions.”

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Written By

Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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