Could long daytime naps be an early sign of dementia?

After a poor night’s sleep, doctors often recommend taking strong naps in order to recover and continue into the next evening. But in older adults, longer naps may be an early sign of dementia.

So far, research aimed at determining how naps affect cognition in adults has had mixed results. Some studies seem to indicate that naps are beneficial for cognition in young adults. Others, done in the elderly, suggest on the contrary that taking naps could be associated with cognitive impairment.

In older adults, naps may be linked to cognitive impairments – CC0

However, many of these studies rely solely on self-report data. However, in some cases, this methodology may not be accurate enough: people with cognitive impairment in particular may have difficulty providing reliable information about the duration or frequency of their naps.

As an epidemiologist who studies sleep and neurodegeneration in older adults, I have investigated whether changes in napping patterns can predict cognitive decline. The results I and my colleagues have shown show that it is normal for naps to increase with age, but excessive elongation can be a sign of cognitive decline.

video : Alzheimer’s disease can be linked to sleep (VO subtitled)

The link between naps and dementia

Disturbed sleep and inappropriate naps are known symptoms associated with mild to moderate forms of Alzheimer’s disease, as well as other forms of dementia in older adults. Souvent, à mesure que la maladie progresse, ces symptômes deviennent plus extrêmes : les patients parviennent de moins en moins à trouver le sommeil lorsqu’ils se couchent, sont plus susceptibles de se réveiller durant la à nuit, et mn som s se clent plus en cl sent During the day.

To examine the link between naps and dementia, my colleagues and I studied a group of 1,401 people with an average age of 81 years. These people participated in the project Impulse memory and aging, a longitudinal study designed to analyze cognitive decline and Alzheimer’s disease. For fourteen years, participants wore a device, similar to a wristwatch, intended to track their movement. Periods of prolonged inactivity have been interpreted as naps.

The Rush Memory and Aging project aims to analyze cognitive decline and Alzheimer's disease
The Rush Memory and Aging Project aims to analyze cognitive decline and Alzheimer’s disease – Drphuc / Pixabay

At the start of the study, nearly 75% of patients showed no signs of cognitive decline. Of the other patients, 4% had Alzheimer’s disease and 20% had mild cognitive decline, which is often a precursor of dementia risk.

Over the years, the daily duration of naps increased for all participants, but we observed differences between people with and those without Alzheimer’s disease. Participants who did not have cognitive impairment nap an average of 11 minutes per year.
In people diagnosed with MCI, this duration more than doubled: nap duration increased an average of 25 minutes per year. Finally, in participants diagnosed with Alzheimer’s disease, this stretch tripled again, to an additional 68 minutes per year, on average.

In the end, we found that older adults who naps at least once a day, or slept more than an hour during the day, were 40% more likely to develop Alzheimer’s disease than those who didn’t nap daily. Those who took naps did not last more than one hour. These results remained unchanged even after correcting for factors such as daily activities, illness, or medication.

A nap is part of the natural aging process, as long as it isn't overly prolonged
Naps are part of the natural aging process, provided they are not excessively prolonged – Tom Ang / Photodisc – Getty Images (via The Conversation)

A nap and the Alzheimer’s brain

Our study shows that longer naps are a normal part of aging, but only to a certain extent. Our colleagues at the University of California, San Francisco have identified a mechanism that may explain why people with dementia take longer and more frequent naps.

They did a post-mortem comparison of the brains of people who died without any cognitive decline with the brains of people with Alzheimer’s disease. The results revealed that in the latter case, three brain regions had fewer neurons (neurons) involved in wakefulness. These neural changes appear to be related to the presence of tangles of tau protein, which are signs of Alzheimer’s disease that form when tau protein, which helps stabilize healthy neurons, eventually forms clumps that impede communication between neurons.

Although our study does not show that increased napping leads to cognitive decline, it does suggest that prolonged napping is a possible signal of accelerated aging. More research will determine whether monitoring the duration of naps can help better detect the onset of cognitive decline.

This analysis was written by Yue Leng, associate professor of psychiatry at the University of California (San Francisco).
The original article was translated (from English) and published on Conversation.

Declaration of interest
● Yue Leng receives funding from the National Institute on Aging.

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