Does drinking coffee reduce the risk of atrial fibrillation? Maybe just a little.

Atrial fibrillation is the most common type of heart arrhythmia in the U.S. and Europe, affecting millions of people every day. A-fib is a condition where your heart beats irregularly and less efficiently than normal. Some people experience a-fib without even being aware of it, but it is a serious condition that leads to an estimated 750,000 hospitalizations per year in the U.S. alone.

The causes of a-fib are not completely understood, but one widespread view is that too much caffeine might trigger it. For example, the American Heart Association’s website says that “Avoiding atrial fibrillation and subsequently lowering your stroke risk can be as simple as foregoing your morning cup of coffee.” Although the site goes on to describe more substantial treatments such as beta blockers and calcium channel blockers, the idea of simply cutting out coffee seems very appealing.

As appealing as it sounds, this advice is wrong, at least for men.

In a study published in 2019 in the Journal of the American Heart Association, Vijaykumar Bodar and colleagues at Harvard Medical School looked at data from nearly 19,000 men who participated in the long-term Physicians’ Health Study. They looked at the risk of atrial fibrillation in men drinking anywhere from no coffee at all to 4 or more cups per day.

They found, somewhat surprisingly, that men who drank 1-3 cups of coffee per day had a 15% lower risk of a-fib compared to men who never or almost never drank coffee. They also found a small hint of a “dosage” effect, with the greatest reduction in risk at about 1.5 cups per day, and less benefit as consumption rose to 4 or more cups.

In a commentary published along with the study, Ryan Aleong and Amneet Sandhu point out that coffee contains a number of ingredients that might explain its cardiovascular benefits. They also point out, though, that the benefits are modest at best.

Unfortunately for women, though, coffee doesn’t seem to have the same benefits for them. Back in 2010, the Women’s Health Study reported that higher caffeine consumption did not increase the risk of a-fib in women, but it didn’t decrease it either. In a subgroup of women drinking the highest amount of coffee, they reported a slight increase in the risk of a-fib, but those women also smoked more often.

(Actually, if you look closely at the numbers in Table 2 of the Women’s Health Study report, women in the group who consumed an average amount of caffeine had a 20% lower risk of atrial fibrillation, consistent with the more recent study in men.)

For those of us who like coffee, this seems to be good news. At worst, coffee isn’t bad for heart health, and at best it might slightly reduce the risk of atrial fibrillation.

Some caveats: although these are large studies with thousands of men and women followed for many years, they rely on self-reporting of coffee consumption, which isn’t perfect. That’s probably the best we can do, though, since it’s impractical to measure caffeine consumption precisely over a long period of time.

The best advice, then, appears to be to keep drinking one or two cups of coffee per day, if you enjoy it. For those who have atrial fibrillation, cutting out that morning coffee, as the American Heart Association suggests, is very unlikely to help.