The Educated Patient Podcast: Coffee, Caffeine and Your Heart, Explained by a Cardiologist

Some people can drink an espresso after dinner and sleep soundly. Others lie awake if they have caffeine after lunch. According to Gregory Marcus, M.D., M.A.S., that difference is real, and it’s written in our genes.

Marcus, a cardiac electrophysiologist, endowed professor in atrial fibrillation research at the University of California, San Francisco (UCSF), and associate chief of cardiology for research at UCSF Health, joined host Mike DeMarco on The Educated Patient Podcast to discuss what the science says about caffeine and heart health. He also chaired the writing group for a newly published American Heart Association scientific statement on caffeine and cardiovascular health.

Why caffeine affects everyone differently

People metabolize caffeine at very different speeds, and a simple genetic test can predict who is fast or slow, Marcus said. Regular use tends to speed up metabolism, while it generally slows with age.

In his team’s CRAVE trial, participants wore heart monitors and fitness trackers while being randomly assigned to drink caffeinated coffee on some days and avoid it on others. On coffee days, people slept about 30 minutes less on average. Slow metabolizers slept almost an hour less, while fast metabolizers saw no change. Participants also took about 1,000 more steps on coffee days.

Marcus noted that caffeine “does not reduce our need for sleep; it just gets in the way of our developing the sensation that we need sleep.”

Coffee and atrial fibrillation

For years, people with atrial fibrillation (AFib), a common irregular heart rhythm, have often been told to avoid coffee. Marcus said that advice was based on conventional wisdom rather than strong data.

His team tested it in a randomized trial of people with AFib who had just undergone a procedure to restore a normal heart rhythm. Those assigned to drink at least one caffeinated coffee a day for six months had a lower risk of AFib returning than those told to avoid caffeine.

For his patients with AFib, the message is reassuring: “If you are enjoying caffeinated coffee, go ahead. You don’t need to avoid it,” he said.

However, the CRAVE trial found that coffee increased premature ventricular contractions, early beats from the heart’s lower chambers, which is now a focus of his research.

Energy drinks are a different story

Marcus cautioned against applying coffee research to energy drinks. “It’s really important to avoid the understandable temptation to just extrapolate from what’s been found in the setting of caffeinated coffee to energy drinks,” he said.

Energy drinks often contain very high concentrations of caffeine along with sugar and other additives. Because caffeine hits so quickly, people can’t gauge how much is too much until it’s too late. He especially discouraged combining them with strenuous workouts.

Practical takeaways

Marcus tells patients not to count coffee toward daily fluid intake and to drink at least as much water as coffee. For people with insomnia, he suggests trying a break from caffeine as an experiment.

His bottom line: “One size does not fit all when it comes to caffeine.”