Napping twice a week lowers risk of CVD
Taking a nap once or twice a week—regardless of how long those naps are—can lower a person’s risk of incident heart disease, researchers report in the latest issue of BMJ Heart.
The relationship between habitual napping and cardiovascular risk has long been a subject of debate, first author Nadine Hausler, of the University Hospital of Lausanne in Switzerland, and co-authors wrote in the journal. Studies across Greece, Costa Rica, the U.S., Japan and Germany have reported conflicting results, and few projects considered nap frequency.
“Most studies only distinguished between nappers and non-nappers or investigated the effect of nap duration on CVD, but did not take the frequency of napping into account,” Hausler et al. wrote. “Further, most studies only focused on CVD mortality, and failed to assess the effect of napping on non-fatal CVD events."
Hausler’s team attempted to correct those shortcomings in a study of 3,462 individuals in a Swiss population-based cohort, all of whom reported their nap frequency and daily nap duration over the course of a week. Participants were followed for an average of 5.3 years and had no history of CVD at baseline.
The majority of subjects in the study—58%—said they hadn’t taken any naps during the previous week, but 19% reported taking one to two naps and 12% reported taking three to five naps. An additional 11% said they’d taken six to seven naps during the week, and those people were more likely to be older, men, have a lower educational status and have a higher BMI. Frequent nappers were also more likely to report excessive daytime sleepiness than non-nappers.
Over 17,976 person-years of follow-up, Hausler and colleagues noted 155 fatal and non-fatal CVD events. People who napped one to two times a week were 48% less likely than non-nappers to experience a CVD event, but the authors didn’t find any link between nap duration and CVD. Neither obstructive sleep apnea nor excessive daytime sleepiness seemed to adjust risk much, either.
Hausler et al. did initially find that subjects who took naps six to seven times a week were 67% more likely to experience a CVD event, but that increased hazard disappeared in adjusted models for a hazard ratio of 0.89.
“We found a J-curved relationship between nap frequency and cardiovascular events,” the authors wrote. “Whereas the increased risk for frequent nappers disappeared with the inclusion of sociodemographic, lifestyle and cardiovascular risk factors, the negative association between napping once or twice a week and cardiovascular events remained.”
Hausler and co-authors said blood pressure and heart rate surge after waking up from an afternoon nap, which might explain increased CVD risk in the short-term. But occasional naps have also been found to be stress-relieving, which could counter that effect and explain why some naps—but not too many—were beneficial in the study population.
“We could speculate that frequent napping may be secondary to impaired sleep quality due to a chronic condition, which may represent an independent risk factor for CVD events,” the team wrote. “In contrast, occasional napping might be a result of a physiological compensation allowing for a decrease in stress due to insufficient nocturnal sleep and thus could have a beneficial effect on CVD events.”
After graduating from Indiana University-Bloomington with a bachelor’s in journalism, Anicka joined TriMed’s Chicago team in 2017 covering cardiology. Close to her heart is long-form journalism, Pilot G-2 pens, dark chocolate and her dog Harper Lee.