December 1, 2023
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A light midday nap improves memory and other types of cognition, and your mood
I have a confession: I sleep. Most days after lunch you will find me sleeping. I used to keep silent about it. Other countries have strong traditions of napping, but here in the United States it is often equated with laziness. In 2019, a US federal agency even announced a ban on sleeping in government buildings.
I’m going public with my napping habit now because, despite what bureaucrats may think, sleep scientists are becoming clearer about the power of napping. That shift is part of the relatively recent recognition that sleep quality and duration are public health issues, says physiologist Marta Garaulet of the University of Murcia in Spain.
For a time, the research was for and against napping. Many studies have shown that mood and cognitive benefits of the midday break, but others found links to poor health, especially in older adults. That made some experts hesitant to “prescribe” naps. However, more recent research has clarified that different types of naps have different effects. Several scientists now think the sweet spot is about 20 to 30 minutes.
The need to take a nap is governed by two physiological processes. One is called homeostatic sleep pressure (HSP) and it increases the longer you are awake. The other has to do with daily circadian rhythms, which leave everyone a little sleepy in the afternoon. Some people, like me, nap habitually even when we get enough sleep at night. Others can’t take a nap unless they are severely sleep deprived. Genes, such as those underlying HSP, drive much of the difference.
In fact, short naps have cognitive benefits, says Michael Chee of the Center for Sleep and Cognition at the National University of Singapore. In a 2022 analysis, his team found especially significant improvements in certain types of memory, information processing speed, and alertness (the ability to respond to an unexpected event, for example, a car swerving). A nap also makes many people feel better. “No one talks about mood enough,” but, Chee says, tired people tend to be moody people.
You don’t need to sleep a lot to see these increases. “Even a short 10-minute nap will refresh you,” says Chee. “If you do it a little longer, the cognitive benefits last a little longer too,” and that’s why half an hour or so has become a good nap period. “You sleep mostly light” during that time, says Ruth Leong, who works with Chee in Singapore, and that makes waking up easier. Leong advises people who work during the normal day to avoid taking naps long after 5 pm so as not to disturb nighttime sleep.
Cognitive benefits appear after naps that last longer than 30 minutes, and those benefits last longer. But longer naps allow a person to sleep more deeply and increase “sleep inertia,” that groggy feeling when waking up. Although lightheadedness can pass relatively quickly and not everyone feels it, many people find it unpleasant.
Longer naps are also associated with some health problems. In a 2023 study of more than 3,000 healthy Europeans with an average age of 41, Garaulet and his colleagues found that those who slept more than 30 minutes at a time were 23 percent more likely to be obese than those who did not sleep. absolutely. (Obesity was calculated using body mass index and several other indicators.) They were also more likely to have a combination of high blood pressure, high cholesterol and other health problems. Additionally, long naps reduce the body’s ability to lose fat on a diet, Garaulet has shown.
But it’s probably an illness causing the extra naps and not the other way around. That is what happens, for example, with Alzheimer’s. Even in younger adults, researchers have found a link between greater brain inflammation and more napping. If someone starts needing frequent naps (more than once a day) and regularly sleeping for more than an hour, that could be a sign of illness, Chee says.
Because my naps tend to last 20 minutes and make me feel alert and productive, I no longer feel embarrassed about them. Instead, I feel lucky that it’s easy for me to nap… and that I’m finishing this column right before lunch.