As we get on in years, most of us find ourselves more and more in need of the odd afternoon nap. But excessive daytime snoozing could be an early indication of cognitive impairment, Alzheimer’s disease and other forms of dementia, a study carried out by researchers based at the University of California and Harvard Medical school have found.


In the study, the team tracked data recorded from more than 1,400 participants with an average age of 81 who wore smart watches that monitored their daily activity.

They then logged any period of more than a few minutes of inactivity the participants spent between the hours of 9am and 7pm. And then assessed changes in their cognitive abilities using lab-based tests once each year.

At the beginning of the study 1203 of the participants had no cognitive impairment. Of these, 290, or 24 per cent, went on to develop Alzheimer’s disease within six years.

Among this group, the team calculated that those who napped for more than one hour a day had a 40 per cent higher risk of developing Alzheimer’s, regardless of the amount and quality of sleep they got during the nighttime.

The findings build on a previous study carried out at the University of Carolina in 2019 that found that the brains of those with Alzheimer’s disease have fewer so-called ‘wake-promoting’ neurons in several areas of their brains.

These differences in brain structure are thought to be linked to tau tangles – a common biomarker of Alzheimer’s disease that involves a misfolding and clumping together of proteins within the brain.

“We found the association between excessive daytime napping and dementia remained after adjusting for nighttime quantity and quality of sleep,” said co-author Yue Leng, of the UCSF Department of Psychiatry and Behavioral Sciences. “This suggested that the role of daytime napping is important itself and is independent of nighttime sleep.

“I don’t think we have enough evidence to draw conclusions about a causal relationship, that it’s the napping itself that caused cognitive ageing, but excessive daytime napping might be a signal of accelerated ageing or cognitive ageing process.

“It would be very interesting for future studies to explore whether intervention of naps may help slow down age-related cognitive decline.”

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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.