No Arrhythmia Risk from Coffee: Title of World's Greatest Beverage Unchallenged

Let’s just call it a health food at this point.

There’s a near truism in dietary science that anything that is too pleasurable is probably not good for you. It holds for ultra-processed foods, refined sugars, alcohol. But there is one stubborn hold out to this trend. One thing you can ingest that provides both pleasure, and, in study after study, health benefits. It’s sort of a unicorn. I’m speaking, of course, of coffee.

Coffee has come a long way since being falsely implicated in causing stomach ulcers or nervous exhaustion. In fact, newer studies have highlighted that coffee drinking is associated with a decreased risk of cancer, diabetes, even overall mortality. You could almost argue it’s a heath food.

Nevertheless, some guideline-making societies have recommended avoiding coffee to certain individuals because it might promote cardiac arrhythmia.

This is in the medical zeitgeist. Coffee makes your heart race. Coffee gives you palpitations. But does it? Or, more meaningfully, does it have any long-term consequences? This study, appearing this week in JAMA Internal Medicine from Gregory Marcus and his team at UCSF suggests quite the opposite. Coffee drinking may, in fact, reduce the risk of arrhythmia.

England, OMG.

The researchers used data from the UK Biobank – a huge cohort of around 400,000 individuals. As this was a UK cohort, its almost all white people and, somehow the most common form of coffee drunk is instant? England, we need to talk.

OK, at enrollment, individuals were asked a slew of questions including how much coffee they drank. They were then followed for about 5 years on average for the development of a cardiac arrhythmia like atrial fibrillation.

And the results are pretty clear – a dose-dependent protective effect. The more coffee you drink, the less likely you are to be diagnosed with atrial fibrillation.

Now – we need to be really careful with studies like this – they can go wrong in some subtle ways.

How this type of study can go wrong

For one, arrhythmia was detected based on diagnosis codes. The authors appropriately excluded patients who had a code for the arrhythmia before they took the coffee survey. But not every arrhythmia gets coded. It’s possible some people may have noticed their heart racing from time to time and held off on drinking coffee either out of caution or because it truly makes things worse.  They then enter the cohort, report not drinking coffee, and sometime later get the official diagnosis of Afib that they actually had all along.

The researchers have a trick up their sleeves though. Genetics. See, it turns out that our genes dictate how fast we metabolize caffeine. The researchers created a polygenic risk score for caffeine metabolism showing, as you might expect, that fast-metabolizers drink a bit more coffee than slow metabolizers.

Regardless of which you were though, your risk of arrhythmia was the same.  The implication here is that there is no non-caffeine substance in coffee that substantially changes your risk of arrhythmia. It doesn’t say much about caffeine itself, though, since – coffee being as ubiquitous as it is – we can more or less determine our own caffeine levels regardless of our metabolism rates.

Is it open-season on rocket fuel? Not really. This study tells us about diagnosed arrhythmias, not transient arrythmias might occur in the setting of high caffeine intake – I think if a patient told me they were getting palpitations after drinking coffee I’d, you know, tell them to stop drinking coffee. But overall, this study provides good reassurance that you’re not doing long-term damage by partaking of the one good thing that doesn’t seem like it’s out to kill you.

A version of this commentary first appeared on medscape.com.