Excessive daytime napping in the elderly an early sign of Alzheimer’s
New research suggests a bidirectional relationship between the daytime sleep behaviours of older adults and cognitive decline – that is to say, “longer and more frequent daytime naps were associated with worse cognition and a higher risk of Alzheimer’s dementia.” Researchers led by a team from the University of California, San Francisco (UCSF) describe this relationship as a “vicious cycle,” whereby excessive daytime napping influences poor cognition and vice versa.
The cycle was seen to get progressively worse as years passed.
According to the findings of a 14-year study on more than one thousand senior citizens, the frequency and duration of naps increased with age. Subjects who were cognitively healthy at the beginning of the study were 40% more likely to develop Alzheimer’s within about six years if they napped at least once a day or napped more than one hour per day. At the same time, subjects clinically diagnosed with Alzheimer’s were seen to double the annual increases in nap duration and frequency compared to those without Alzheimer’s.
[Each subject wore motion-tracking devices and naps were calculated by prolonged periods of inactivity during the day. Annual tests were used to measure cognitive decline.]
The researchers note that the increase in napping may be due to fewer wake-promoting neurons in three brain regions of Alzheimer’s patients. These neuronal changes are linked to tau tangles – a hallmark of Alzheimer’s, characterised by increased activity of enzymes causing the protein to misfold and clump.
“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 Dr. Yue Leng of the UCSF Department of Psychiatry and Behavioral Sciences. “It would be very interesting for future studies to explore whether intervention of naps may help slow down age-related cognitive decline.”
Dr. 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 remained, suggesting excessive daytime napping is not simply a person making up for fragmented or disturbed nighttime sleep.
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