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If you're a fan of lengthy daytime naps, you may want to rethink your habit, according to a meta-analysis of research presented today at the European Society of Cardiology's annual meeting.
Though only the abstract of the study is currently available, the authors, who are from Guangzhou Medical University in China, shared preliminary findings, which suggested that naps for longer than an hour can increase a person's risk of heart disease and early death.
The researchers looked at 20 previous studies on naps, heart disease, and death risk, including data on 313,651 people, of whom a third (39%) reported taking regular naps.
They concluded that naps of any duration increased a person's risk of death by 19%, and said it could be because participants used naps as replacements for a full night of sleep, which is essential for allover health.
But people who took long naps, of 60 minutes or longer, had the highest risk, they said. According to the study, those people were 30% more likely to suffer premature death, and 34% more likely to develop heart disease, than people who didn't nap at all.
The study's findings build on existing research that suggests long naps can contribute to inflammation, high blood pressure, and diabetes, according to lead study author Dr. Zhe Pan. At the same time, the results conflict with research that's found naps to improve brain function and lower blood pressure.
Short Naps Could Improve Heart Health for People Who Don't Get Enough Sleep
There was one nap-positive finding in the new study: short naps in the 30- to 45-minute range could improve a person's heart health.
"The results suggest that shorter naps might improve heart health in people who sleep insufficiently at night," as opposed to longer naps that could increase inflammation and mess with a person's nighttime sleep, Pan said in the release.
Previous research found a 60-minute midday nap can lower a person's blood pressure almost as much as a blood-pressure medication can. If a person's blood pressure is too high, it can lead to a heart attack.
The study did have caveats. Since it was an analysis of previous studies, it's possible other factors like participants' lifestyles, ages, or underlying conditions contributed to the results. Therefore, the study authors can't say there's a direct link between naps and heart disease or death risk.
Naps Shouldn't Replace Consistent Full Nights of Sleep
Other research has found naps to be beneficial to brain function, but it all depends on the duration of the nap and how it's being used.
If a person consistently uses a nap to replace sleep lost during the night, it's likely their midday snooze is detrimental to their health.
"A common view is that napping improves performance and counteracts the negative consequences of 'sleep debt'. Our study challenges these widely held opinions," Pan, the new study author, said in a press release.
Indeed, the authors of a December 2016 study found naps between 30 and 60 minutes improved concentration and memory formation in adults who were 65 and older. But longer naps had the opposite effect, decreasing the participants' cognitive abilities.
"I consider napping to be a good thing, but it needs to be taken in the context of the person and his or her own sleep cycles and body," Dr. Charlene Gamaldo, medical director of Johns Hopkins Sleep Disorders Center, said in an article analyzing the 2016 study.
Long naps can mess with a person's nightly sleep routine and lead to lost sleep, which can raise a person's blood pressure and contribute to overall worse health outcomes, according to the Cleveland Clinic.
For that reason, the American Sleep Association recommends keeping midday naps short, and focusing on full nights of sleep that start and end around the same time each day.
And if you need a midday snooze here and there, that's OK, according to ASA.