A team of Spanish cardiology researchers also found that how much you sleep at night can make a lasting impact, too.
Whether you’re fighting daytime drowsiness after a big lunch or a poor night of sleep, taking a short nap can be a good decision—for more reasons than you might think. Past research indicates that napping can positively impact the body by boosting cognitive health and lowering the risk of type 2 diabetes, just to name a few potential benefits. However, a July 2025 study found that there’s one potentially serious downside to napping for 30 minutes or more—and it has to do with heart health.
That study, published in the European Journal of Preventive Cardiology by a group of Spanish cardiology and preventative health researchers, found that the way we sleep may play an important role in heart rhythm health. The team looked at how daytime napping and nighttime sleep duration were linked to atrial fibrillation (often referred to as AFib), a common heart condition that causes an irregular and often rapid heartbeat. According to the U.S. Centers for Disease Control and Prevention (CDC), atrial fibrillation affects at least 12 million U.S. adults.
The research drew on data from The SUN Project, a long-term health study involving more than 20,800 Spanish university graduates who were free of AFib when the study began. Participants were followed for an average of 15 years, and researchers collected information via questionnaires regarding how long they typically napped and slept. Any new cases of AFib were carefully confirmed by a cardiologist.
Over the course of the study, 163 people developed atrial fibrillation. When researchers compared sleep patterns, they discovered that long daytime naps—30 minutes or more—were linked to a 62% higher risk of AFib compared with short naps of less than half an hour. Those who skipped naps altogether did not show a significant difference in risk.
These findings are a cause for concern because, according to the American Heart Association, atrial fibrillation can lead to blood clots, stroke, heart failure and other cardiovascular complications—“even when you don’t feel symptoms.”
The study also found that nighttime sleep patterns mattered. People who slept either too little (under six hours) or too much (over eight hours) faced an 89% higher risk of AFib compared with those who slept between six and eight hours a night.
But the greatest risk appeared among participants who both took long naps and had inadequate night sleep—those individuals had an atrial fibrillation risk that was three times greater versus those who slept and napped within healthier ranges.
Since the study’s findings suggest that both daytime rest habits and nighttime sleep duration may affect heart rhythm health, it’s a helpful reminder to aim for both the right quality and quantity of sleep each day. While naps can be refreshing, keeping them short—and ensuring adequate sleep at night—could yield positive results in the long run.
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