Friday 18 March 2022

Excessive daytime napping could be early sign of Alzheimer’s disease


Napping for longer than one hour or several times a day could be an early sign of Alzheimer’s disease according to new research. It’s suggested excessive daytime napping shares a bidirectional relationship with cognitive decline, both reflecting and shaping changes in the brain.

The relationship between Alzheimer’s disease and disrupted sleep patterns is well established. Researchers have found disrupted or fragmented sleep can accelerate the pathological signs of Alzheimer’s, but are daytime naps really a threat to long-term brain health?

"Daytime sleep behaviors of older adults are oftentimes ignored, and a consensus for daytime napping in clinical practice and health care is still lacking," explained Peng Li, co-first author on the new study.

The new study looked at novel data from an ongoing long-term project tracking memory and aging in more than one thousand senior citizens. For 14 days every year the participants wore motion-tracking devices and naps were calculated by prolonged periods of inactivity during the day.

Each participant was enrolled at an average age of 81 and followed for 14 years. Annual tests were used to measure cognitive decline.

The findings revealed a distinct bidirectional relationship between daytime napping and cognitive decline. In general, the frequency and duration of naps increased with age, however, those subjects diagnosed with Alzheimer’s were seen to double the annual increases in nap duration and frequency compared to those without Alzheimer’s.

“Longer and more frequent daytime naps were associated with higher risk of Alzheimer's dementia,” the researchers wrote in the new study. “Interestingly, more excessive (longer or more frequent) daytime napping was correlated with worse cognition a year later, and conversely, worse cognition was correlated with more excessive naps a year later.”

So what comes first – excessive napping or cognitive decline?

The researchers describe this relationship as a “vicious cycle,” whereby one influences the other and vice versa. Those clinically diagnosed with Alzheimer’s certainly displayed subsequent increases in nap frequency and duration, but those who were cognitively healthy at the beginning of the study were 40 percent more likely to develop Alzheimer’s within six years if they napped at least once a day or napped more than one hour per day.

Yue Leng, co-senior author on the study, said it is impossible to tease out causal direction from this particular dataset. At this stage it is possible excessive daytime napping can directly play a role in accelerating brain aging, but it is also possible the napping is a very early preclinical sign of Alzheimer’s.

“I don’t think we have enough evidence to draw conclusions about a causal relationship, that it’s the napping itself that caused cognitive aging, but excessive daytime napping might be a signal of accelerated aging or cognitive aging process,” said Leng. “It would be very interesting for future studies to explore whether intervention of naps may help slow down age-related cognitive decline.”

Leng also pointed out the association between daytime napping and cognitive decline was not influenced by nighttime sleep quality. The researchers adjusted for the quantity and quality of nighttime sleep and the association still remained, suggesting excessive daytime napping is not simply a person making up for fragmented or disturbed nighttime sleep.

Kun Hu, co-senior author on the study, said the main takeaway from the findings is for closer surveillance of daytime sleep habits in the elderly. According to Hu, changes to napping habits over time may be a robust early signal of preclinical Alzheimer’s disease.

"Our hope is to draw more attention to daytime sleep patterns and the importance of patients noting if their sleep schedule is changing over time," said Hu. "Sleep changes are critical in shaping the internal changes in the brain related to the circadian clocks, cognitive decline and the risk of dementia."

The new study was published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association.

Sources: Brigham and Women’s HospitalUCSF

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