Can longer daytime naps be an early sign of dementia?

After a poor night’s sleep, doctors often recommend taking power naps in order to recuperate and hold on until the following evening. But in older people, longer nap times could be an early sign of dementia.

So far, research aimed at determining how napping affects cognition in adults has had mixed results. Some studies seem to indicate that napping is beneficial for cognition in young adults. Others, conducted on older adults, suggest on the contrary that taking a nap could be linked to the occurrence of cognitive impairments.

In older adults, napping may be linked to the occurrence of cognitive impairments – CC0

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

As an epidemiologist studying sleep and neurodegeneration in the elderly, I investigated whether changes in nap patterns could be predictors of cognitive decline. The results that I obtained with my collaborators show that it is normal for the duration of naps to increase as one ages, but that excessive elongation could well be a sign of cognitive decline.

VIDEO : Sleep and Alzheimer’s disease could be linked (VO subtitled)

Link between napping and dementia

Sleep disturbances and inopportune naps are well-known symptoms associated with mild to moderate forms of Alzheimer’s disease, as well as other forms of dementia in the elderly. Often, as the disease progresses, these symptoms become more extreme: patients are less and less able to fall asleep when they go to bed, are more likely to wake up during the night, and therefore more prone to feeling drowsy during the day.

To examine the link between napping and dementia, my colleagues and I studied a group of 1401 people with an average age of 81 years. These people participated in the project Memory Rush and Aginga longitudinal study to analyze cognitive decline and Alzheimer’s disease. For fourteen years, participants wore a device, similar to a wristwatch, intended to track their mobility. Periods of prolonged inactivity were interpreted as naps.

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

At the start of the study, approximately 75% of patients showed no signs of cognitive decline. Among the other patients, 4% were affected by Alzheimer’s disease and 20% were affected by a moderate cognitive decline, which is frequently a harbinger of the risk of onset of dementia.

Over the years, the daily duration of naps has increased for all participants, however we have seen differences between people with Alzheimer’s disease and those without. The naps of participants who did not develop cognitive impairment lengthened by an average of 11 minutes per year.
In people for whom a diagnosis of moderate cognitive impairment was established, this duration more than doubled: the duration of naps increased by an average of 25 minutes per year. Finally, in participants for whom a diagnosis of Alzheimer’s disease was made, this lengthening tripled again, reaching an additional 68 minutes per year, on average.

Ultimately, we found that older people who took a nap 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. did not take a daily nap or those who took a nap that did not last longer than one hour. These results remained unchanged even after correction of factors such as daily activities, illnesses or taking medication.

The nap is part of the normal aging process, provided that its duration does not lengthen excessively
Napping is part of the normal aging process, provided its duration is not excessively lengthened – Tom Ang/Photodisc – Getty Images (via The Conversation)

​Nap and the “Alzheimer’s” brain

Our study demonstrates that longer nap times 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, more frequent naps.

They proceeded to the post-mortem comparison of the brains of people who died without having been affected by any cognitive decline with the brains of people affected by Alzheimer’s disease. The results revealed that in the latter, three brain regions harbored fewer nerve cells (neurons) involved in wakefulness. These neuronal changes appear to be linked to the presence of Tau protein aggregates, markers of Alzheimer’s disease that form when said Tau protein, which helps stabilize healthy neurons, forms clumps that eventually impede communication between neurons.

Although our study does not demonstrate that increased naps lead to cognitive decline, it does indicate that prolonged naps are a potential signal of accelerated aging. Further research would determine if monitoring the duration of naps could help better detect the onset of cognitive decline.

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

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

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