Taking a daytime nap once or twice a week may halve the risk of cardiovascular events, such as heart attacks, strokes, and heart failure.
This is the main takeaway of an observational study appearing in the BMJ journal Heart.
Nadine Häusler, Ph.D., from the department of internal medicine at Lausanne University Hospital, in Switzerland, is the first author of the study.
As Häusler and colleagues explain in their paper, much controversy has surrounded the relationship between daytime napping and cardiovascular health.
Some previous studies, referenced by the authors, have found a lower risk of coronary heart disease among daytime nappers, while others have found a higher risk of cardiac events or cardiovascular mortality among those who regularly nap during the day.
To help settle the controversy, Häusler and the team set out to examine the link between napping and fatal and nonfatal cardiovascular events in a cohort of 3,462 adults in Switzerland.
Häusler and colleagues had access to medical data from participants in the CoLaus cohort study.
The participants were between 35 and 75 years of age when they enrolled in the CoLaus study and did not have a history of cardiovascular problems at baseline, that is, in 2003–2006.
Häusler and the team had access to self-reported sleeping patterns and continual health monitoring over an average period of 5 years, as part of the CoLaus study.
When the participants were asked about their sleeping and napping patterns, more than half reported no naps in the previous week, almost 20% said they had napped once or twice, about 12% said they had napped 3–5 times, and a similar number said they had napped 6–7 times.
Those who napped more frequently tended to be older, overweight males who smoked. These participants also tended to sleep for longer at night, have sleep apnea, and feel more sleepy during the day.
During the 5-year monitoring period, 155 cardiovascular events occurred. To assess the association between naps and cardiovascular events, the researchers accounted for potential confounders, such as age or heart disease risk factors, such as hypertension.
The researchers found that taking 1–2 weekly naps during the day was linked with 48% lower chances of having a heart attack, stroke, or heart failure, compared with those who did not nap at all.
However, the analysis revealed no link between cardiovascular events and the duration of the naps.
Häusler and colleagues conclude, “Subjects who nap once or twice per week have a lower risk of incident [cardiovascular disease] events, while no association was found for more frequent napping or napping duration.”
“Nap frequency may help explain the discrepant findings regarding the association between napping and [cardiovascular disease] events.”
Yue Leng, Ph.D., and Dr. Kristine Yaffe, of the University of California, San Francisco, independently comment on the findings in a linked editorial.
They say that it is “premature to conclude on the appropriateness of napping for maintaining optimal heart health,” given that we lack a standard definition or measurement of naps.
However, they add, “While the exact physiological pathways linking daytime napping to [cardiovascular disease] risk is not clear, [this research] contributes to the ongoing debate on the health implications of napping and suggests that it might not only be the duration, but also the frequency that matters.”