An afternoon nap may seem like a simple pleasure, but new research suggests that people who frequently nap have a greater chance of developing high blood pressure and having a stroke.
The new peer-reviewed study, published in Hypertension, an American Heart Association journal, is the first to use both observational analysis of participants over a significant period of time and Mendelian randomization—a genetic risk validation to investigate whether frequent napping was associated with high blood pressure and ischemic (blood clotting) stroke.
Sleep expert Michael Grandner, co-author of the AHA's new cardiovascular health score, said in a statement that the study echoes previous research showing that taking more naps seems to reflect an increased risk for heart problems. “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," he said.
The researchers looked at 358,451 participants free of hypertension or stroke from UK Biobank, a large biomedical database and research resource that followed UK residents from 2006 to 2010. Using these participants, they analyzed the association between napping and first-time reports of stroke or high blood pressure, with an average follow-up report of about 11 years. Participants were split into groups based on self-reported napping frequency: “never/rarely,” “sometimes,” or “usually.”
"Poor sleep at night is associated with poorer health."
Michael Grandner
The results indicated that compared to people who reported never taking a nap, participants who usually nap had a 12% higher likelihood of developing high blood pressure and 24% higher likelihood of having a stroke. Researchers also found that participants younger than age 60 who usually napped had a 20% higher risk of developing high blood pressure compared to people the same age who never did. After age 60, usual napping was associated with 10% higher risk of high blood pressure compared to those who reported never napping.
Who is the typical napper?
According to the study, a higher percentage of often-nappers were men, had lower education and income levels, and reported cigarette smoking, daily drinking, insomnia, snoring and being an evening person compared to never- or occasional-nappers. Higher napping frequency was also related to the genetic tendency for high blood pressure risk.
These findings remained true even after researchers excluded people at high risk for hypertension, such as those with type 2 diabetes, existing high blood pressure, high cholesterol and sleep disorders and who did night-shift work.
Notable limitations to the study are that researchers only collected daytime napping frequency, not duration, so there is no information about how or whether the length of nap affects blood pressure or stroke risks. Additionally, nap frequency was self-reported without any objective measurements.
“These results are especially interesting since millions of people might enjoy a regular, or even daily nap,” according to Prof. E. Wang, chair of the Department of Anesthesiology at Xiangya Hospital Central South University, and the study’s corresponding author.