Sleep is good for the brain. But what about nap? Research raises puzzling questions.

A recent study looked at the relationship between napping and Alzheimer’s disease over 14 years. Researchers at Brigham and Women’s Hospital, the Rush Alzheimer’s Disease Center, and the University of California San Francisco, found that the progression of Alzheimer’s disease led to more napping, and also that people who napped a lot were at higher risk of developing Alzheimer’s.

Among the participants who had no symptoms of cognitive impairment at the outset of the study, those who took longer or more frequent naps were more likely to later be diagnosed with Alzheimer’s.

Researchers have long observed a connection between sleep and dementia. People with Alzheimer’s disease sleep poorly, taking a long time to fall asleep and awakening often in the night. Until a couple of decades ago, it was thought that the process went in one direction — that Alzheimer’s causes sleep disruptions, said Adam P. Spira, a professor and sleep researcher at the Johns Hopkins Bloomberg School of Public Health.

But recent studies suggest a much more complex interaction. Poor sleep leads to worse cognitive performance and a higher risk of dementia. So it’s not just that Alzheimer’s wrecks sleep. Sleep deprivation often precedes Alzheimer’s, and might contribute to its development.

In 2009, a study showed that sleep-deprived mice had greater amounts of a protein called amyloid in their brains than their well-rested peers. Amyloid levels drop during sleep, but remain high during wakefulness. When amyloid clumps into plaques, it becomes a hallmark of Alzheimer’s disease.

“That was the moment things flipped,” Spira said. Researchers, he said, started to think: “Maybe poor sleep is leading to cognitive impairment.”

That notion was boosted when a study in people found that those who reported shorter sleep duration and worse sleep quality had more amyloid in their brains.

“Sleep on a nightly basis might remove these dangerous toxins and potentially reduce the risk of dementia,” said Rebecca Robbins, a sleep scientist at Brigham and Women’s, who published a study last year showing that people who slept fewer than six hours a night and those who took longer than 30 minutes to fall asleep were more likely to develop dementia.

This all sounds like good news for those who nap a lot, right? If too little sleep leads to dementia, wouldn’t loads of sleep keep it at bay?

Alas — naps, too, have been linked to poor health outcomes, including dementia.

“It is counterintuitive. You think sleeping is good,” said Dr. David Holtzman, scientific director of the Hope Center for Neurological Disorders at the Washington University School of Medicine in St. Louis. “That’s true — if it’s not being instigated by a particular part of the brain being damaged.”

In other words, an elderly person nodding off alone in their living room may be experiencing something quite different from a power nap.

Often people sleep extra because they’re sick and need to heal. Or they sleep during the day because they’re up half the night. In those cases, naps are a symptom of something else gone awry.

But the people in the recent napping study weren’t sick and weren’t sleeping too little, and those who napped a lot still faced a higher risk of Alzheimer’s.

It’s possible that napping somehow promotes Alzheimer’s, but there’s no direct evidence for a causal connection. Instead, many experts believe, it’s more likely that napping is an early sign of brain degeneration that starts before symptoms emerge.

“As you start to develop Alzheimer’s-type changes in the brain, those changes are probably leading to damage in parts of the brain that control your ability to stay awake,” Holtzman said. “It’s like a symptom of pathology in the brain that occurs before you show memory impairment.”

In a study published in 2013, Holtzman’s team measured the amyloid levels of people who were cognitively normal. Those who had amyloid plaques, a sign of Alzheimer’s, napped more, he said.

Napping can also interfere with the body’s natural daily rhythms, known as the circadian clock.

Daytime napping damages nighttime sleep, especially if it occurs late in the day, Robbins said. That leads to the need for more daytime naps, in a vicious cycle of sleepless nights and sleepy days.

In the recent napping study from the Brigham, participants wore a device on their wrists to track their movements. The device is often used to detect when people seem to be asleep. Although people in the study slept enough hours, the study revealed nothing about the quality of their sleep.

“We really don’t know what’s going on during the night. We don’t know the sleep structure. We don’t know whether they’re having a good quality nighttime sleep,” said Peng Li of the Brigham’s Division of Sleep and Circadian Disorders and one of the study’s authors.

Perhaps the daytime snoozers were sleeping lightly at night and were merely making up their sleep debt during the day. And perhaps, as the researchers acknowledged, they weren’t napping at all. The device measures motion only; it’s possible these elderly participants were in moments of prolonged repose but not asleep.

Li cautioned against overinterpreting the findings, saying his research points to the need for more studies with more accurate methods of detecting sleep.

“We do want to know whether there’s a causal relationship” between excessive napping and dementia, he said. But more likely, there could be a common mechanism that drives both daytime slumber and the development of dementia.

So, you may wonder, if an elderly relative is napping a lot, should you wake them up?

Most of the experts consulted said yes.

“When you nap a lot during the day, it’s harder to get a good night’s sleep,” Holtzman said. “We recommend trying to keep people awake during the daytime.” He also recommends turning up the lights, opening windows, and engaging the person in an activity.

“Don’t just think about sleep as being this one thing you want to fix,” said Sara Mednick, professor of cognitive science at the University of California Irvine, who wrote a book about napping. “Think about the aging person as an entire whole person. All the things they’re doing during the day are impacting how restorative their sleep will be.”

How about younger, healthier people? Are naps good for them?

The consistent response from all corners was: Yes. Followed by a proviso: as long as the naps are intentional, well-timed, and not too long.

Robbins, of the Brigham, recommends scheduling your nap sometime between 2 pm and 4 pm, a time of day when many feel drowsy and body temperature tends to drop.

“Don’t be afraid of napping,” Mednick said. “Sleep should be in consolidated ends. If you’re going to nap, make it be an intentional consolidated nap, not dozing off.”

Mednick said humanity is divided evenly between those who like to nap and those who don’t. Those who love napping find it automatically restorative. Those who don’t enjoy it get little benefit.

So when you face the question: to nap or not to nap? The answer is, do what works for you, but do it on purpose.


Felice J. Freyer can be reached at [email protected] Follow her on Twitter @felicejfreyer.

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