Clark Gable famously quipped, “I never laugh before I’ve had my coffee.” If you’ve been unhappily sipping only decaf because of a heart arrhythmia, here’s news that could put the real McCoy back in your cup—and maybe an early-morning smile on your face! According to new research, caffeine does not put your heart at risk…and may actually protect it.

More than 80% of US doctors advise their patients with abnormal heart rhythms (arrhythmias) such as atrial fibrillation (AFib) to avoid caffeine. However, that advice may be reversed, thanks to the largest review to date of studies on the effects of caffeine on abnormal heart rhythms. Researchers in Australia analyzed 19 major studies involving hundreds of thousands of arrhythmia patients. Results: The evidence suggests that caffeine does not increase the risk for arrhythmia in most such people…and may even prevent arrhythmias in some people.

For example…

  • Of eight studies involving more than 200,000 patients with arrhythmias of the lower-heart chambers (ventricular arrhythmias), six studies found no link between caffeine and episodes of arrhythmia…and two studies linked arrhythmia only to very high caffeine consumption (equivalent to more than nine cups of coffee per day).
  • In six studies of more than 200,000 people with AFib (arrhythmia of the upper chambers of the heart), drinkers of caffeinated coffee had 6% fewer AFib episodes than noncoffee drinkers.

One reason that caffeine might actually reduce arrhythmias in some people is that it blocks adenosine, a chemical found in the body that triggers arrhythmia. The antioxidants in caffeine may further protect against arrhythmia. The researchers also pointed out that although caffeine stimulates the heart and can cause it to beat rapidly, it does not seem to cause it to beat abnormally.

Before you run to the nearest Starbucks for a double espresso, there are some caveats. First, if your doctor told you to avoid caffeine, don’t start consuming it without checking with him/her first. (You might want to bring this article with you.) A small percentage of people are unusually sensitive to caffeine, and in these people caffeine can cause heart palpitations. There might be other reasons to avoid caffeine that are particular to your health situation.

Also, while daily consumption of up to 300 mg of caffeine—the amount in about three cups of coffee or about six cups of regular tea—was found to be safe and possibly protective, more was not. And caffeine-containing energy drinks should be avoided if you have a heart arrhythmia. They can have up to 500 mg of caffeine in a single serving and may also contain other heart stimulants, such as ephedra and/or ginseng.