“This may be because, although taking a nap in itself is not harmful, many people who do may do so because of poor sleep at night. Poor sleep at night is associated with poor health, and naps aren’t enough to compensate for that,” clinical psychologist Michael Grandner said in a statement. Grandner directs the Behavioral Sleep Medicine Clinic at Banner-University Medical Center in Tucson, Arizona, and did not participate in the study.
Study participants who typically nap during the day were 12% more likely to develop high blood pressure over time and 24% more likely to have a stroke compared to people who never nap .
The findings held true even after the researchers excluded people at high risk for hypertension, such as those with type 2 diabetes, existing high blood pressure, high cholesterol, sleep disturbances, and who worked night shifts. .
“The results demonstrate that napping increases the incidence of hypertension and stroke, after adjusting for or controlling for many variables known to be associated with the risk of cardiovascular disease and stroke,” said Dr. Phyllis Zee, director of the Center for Circadian and Sleep Medicine at Northwestern School of Medicine at Feinberg University in Chicago.
“From a clinical perspective, I think this highlights the importance for health care providers to regularly ask patients about napping and excessive daytime sleepiness and to assess other contributing conditions that may modify the risk of cardiovascular disease,” said Zee, who was not involved in the study.
Longer naps are worse
The study used data from 360,000 participants who had given information about their napping habits to the UK Biobank, a large biomedical database and research resource that tracked UK residents from 2006 to 2010.
Participants in the UK study regularly provided blood, urine and saliva samples and answered questions about napping. four times during the four years of study. However, the study only collected nap frequency, not nap duration, and relied on self-reports of naps, a limitation due to imperfect recall.
“They haven’t defined what a nap should be. If you’re going to sleep for an hour, two hours, for example, that’s not really a nap,” said sleep specialist Dr. Raj Dasgupta, an associate. professor of clinical medicine at the Keck School of Medicine at the University of Southern California.
“A 15 to 20-minute cooling nap between noon and 2 p.m. is 100 percent the answer if you’re sleep deprived,” said Dasgupta, who wasn’t involved in the study. “If you have chronic insomnia, we don’t encourage napping as it keeps you awake at night.”
Most of the people in the study who took regular naps smoked cigarettes, drank daily, snored, had insomnia, and reported being an evening person.
Many of these factors could impact the quality and quantity of a person’s sleep, Dasgupta said. Poor sleep causes “excessive daytime fatigue which can lead to excessive daytime naps,” he said.
“I believe napping is a warning sign of an underlying sleep disorder in some people,” he added. “Sleep disturbances are linked to increased stress and weight-regulating hormones that can lead to obesity, high blood pressure, type 2 diabetes – all risk factors for heart disease.”