A new meta-analysis, encompassing more than 20 studies, suggests daytime naps lasting more than 60 minutes can be linked to higher rates of all-cause mortality and poor cardiovascular health. Although the finding is only correlational, the researchers suggest it is safest to keep your siestas to less than one hour.
Sleep is important. That much is obvious. Scientists may only now be starting to uncover exactly how good sleep hygiene is beneficial to our health, but it’s clear how fundamental getting between seven and eight hours of solid slumber a night actually is.
But what about naps? A little sneaky early afternoon bit of shut-eye is increasingly being found to confer a broad assortment of cognitive benefits, from helping us memorize information, to generally improving brain health.
This new research, presented recently at the European Society for Cardiology 2020 Congress and not yet published in a peer-reviewed journal, looks at the subject of napping from a different perspective. Instead of concentrating on the acute cognitive effects of a nap, this research investigates the long-term practice of napping, and whether there is a relationship between cardiovascular health, all-cause mortality, and daytime siestas.
“Daytime napping is common all over the world and is generally considered a healthy habit,” says an author on the study, Zhe Pan from China’s Guangzhou Medical University. “A common view is that napping improves performance and counteracts the negative consequences of 'sleep debt'. Our study challenges these widely held opinions.”
The analysis included data from around 20 studies, encompassing more than 300,000 people, and found subjects who regularly napped for more than 60 minutes each day had a 34 percent higher chance of developing cardiovascular disease and a 30 percent higher risk of all-cause death, compared to those who did not nap at all.
Those subjects napping for less than 60 minutes still showed a small increase in all-cause mortality, but no increased risk of cardiovascular disease. Pan notes this may suggest some heart health benefits to short daytime naps.
“The results suggest that shorter naps (especially those less than 30 to 45 minutes) might improve heart health in people who sleep insufficiently at night,” says Pan.
Importantly, when the researchers accounted for night-time sleep durations the negative health associations with daytime napping, of any duration, disappeared. So napping for more than an hour during the day was only associated with higher rates of all-cause death in subjects who slept for more than six hours per night.
What this finding suggests is the potential negative outcomes from daytime naps are linked more generally to oversleeping, and it's not unreasonable to hypothesize people with excessive levels of fatigue needing that much extra sleep may be suffering from other underlying health conditions. So although this new research certainly identifies a correlation, it cannot determine a causal connection. The need for long daytime naps could be more a sign of other health problems rather than a direct cause of ill health.
“If you want to take a siesta, our study indicates it’s safest to keep it under an hour,” adds Pan. “For those of us not in the habit of a daytime slumber, there is no convincing evidence to start.”
While the jury may be out on the long-term health effects of excessive daytime napping, there is a large body of research on the immediate effects from short bouts of afternoon shut-eye. So what is the optimal napping time for a quick siesta?
An often cited NASA study from 1995 looked at how strategic naps can improve operational performance in certain settings. The research examined pilots on long-haul flights and ultimately suggested 26 minutes is the optimal nap time to balance cognitive benefits against that groggy sensation occasionally experienced upon waking, called sleep inertia.
A more specific Australian study in 2006 compared the effects of five-, 10-, 20-, and 30-minute naps, concluding 10 minutes to be the nap sweet spot. That study found 10-minute naps produced the greatest improvements in all outcome measures, while 30-minute naps began to result in signs of sleep inertia.
In the end, as with most things, the best answer is wholly subjective and dependent on one’s individual sleep patterns. If you are sleeping a healthy eight hours a night you shouldn’t need a daytime nap, but if you're not a great sleeper then a short afternoon nap could be beneficial.
The new research is yet to be published or peer-reviewed but was presented recently at the European Society for Cardiology Annual 2020 Congress.
Source: European Society for Cardiology
