A new study reveals that frequent naps may lead to high blood pressure and stroke. Chinese researchers from Xiangya Hospital Central South University analyzed whether napping regularly posed a threat to cardiovascular health and found that people who take naps have a 12% higher likelihood of developing high blood pressure and a 24% higher risk of having a stroke compared to those who rarely or never nap.

“These results are especially interesting since millions of people might enjoy a regular, or even daily nap,” says Dr. E Wang, one of the study authors, according to a news release from the American Heart Association. This is the first study to examine both observational analysis of participants over a long period of time, and Mendelian randomization, a genetic risk validation, to find whether frequent napping was associated with high blood pressure and ischemic stroke.

Researchers gathered information from more than 500,000 participants in the U.K. Biobank, a large biomedical database and research resource containing anonymous genetic, lifestyle and health information. The participants ranged in age between 40 and 69 and lived in the U.K. between 2006 and 2010, says Study Finds. The researchers collected data from blood, urine, and saliva samples, and lifestyle details.

After rejecting the records of study subjects who already had a stroke or high blood pressure, the researchers were left with a pool of 360,000 people. They divided these subjects into groups based on self-reported napping. The categories of frequency were “never/rarely,” “sometimes,” and “usually.”

Overall, people who said they usually nap had a 12% higher risk of developing high blood pressure and 24% higher risk of having a stroke compared to other participants who rarely napped. Surprisingly, people under the age of 60 had a 20% higher risk of developing hypertension, while after age 60, napping was associated with 10% higher risk of high blood pressure compared to those who reported never napping.

The study also found that if napping frequency increased by one category, from never to sometimes, or from sometimes to usually, high blood pressure rose by an incredible 40%.

“This may be because, although taking a nap itself is not harmful, many people who take naps may do so because of poor sleep at night. Poor sleep at night is associated with poorer health, and naps are not enough to make up for that,” explained Michael A, Grandner, a sleep expert and director of the Sleep and Health Research Program at the University of Arizona. Grander is a co-author of the American Heart Association’s new Life's 8 Essential cardiovascular health score, which added sleep duration in June 2022 as its eighth metric for measuring optimal heart and brain health. “This study echoes other findings that generally show that taking more naps sems to reflect increased risk for problems with heart health and other issues.”

The American Heart Association points out several factors that may affect the study’s conclusions. Firstly, they only collected data on napping frequency, not duration, so there is no information if the length of daytime napping impacts cardiovascular risks. Secondly, the napping data was self-reported, which eliminates objective measurements. And lastly, the participants were mostly middle-aged to elderly with European ancestry, so the results, while interesting, may not be generalized to all populations.