Sleep is important for the brain – and research has repeatedly been linked to dementia, including Alzheimer’s disease. Apparently, this applies not only to nighttime sleep, but also to afternoon naps – as a new study shows.
What’s a quiet daytime nap got to do with Alzheimer’s disease? A lot, as American researchers have just shown. Napping during the day is obviously not just a sign that a person may already have Alzheimer’s disease. It also indicates before the disease that there is an increased risk of this form of dementia.
How was the study?
The study was conducted by a research team from Harvard and the University of San Francisco. Their study was based on data from 1,401 older adults who had participated in the Rush Memory and Aging Project at the Rush Alzheimer’s Disease Center in Chicago for 14 years.1 The average age of the group of participants was 81 years old and about 75% were women. At the start of the study, 75.7% of the elderly had no cognitive impairment. 19.5% already had mild cognitive impairment, while 4.1% were patients with Alzheimer’s disease.
As part of the project, subjects wore trackers that recorded their movements. A prolonged period of inactivity between 9 a.m. and 7 p.m. was counted as a nap. This tracker was used by seniors for up to 14 days at a time and recorded data around the clock during that time. Additionally, study participants underwent a series of neurological tests once a year to assess their cognitive abilities.
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Alzheimer’s patients sleep six times longer
In fact, the data from the long-term study yielded some interesting insights into the link between napping and Alzheimer’s disease. It turned out that the duration of the nap seems to play a role. In test subjects who started out healthy and showed no cognitive decline during the study period, daily naps increased by an average of eleven minutes per year. This therefore seems to represent a “normal” adjustment in old age.
Those who developed mild cognitive impairment during the study period had a double rate of increase, totaling 24 minutes per day. The test subjects’ sleep duration increased rapidly after they were diagnosed with Alzheimer’s disease: their daily nap increased by 68 minutes.2
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Sleeping more than an hour a day increases Alzheimer’s risk by 40%
But the researchers discovered even more. Namely, the link between napping and Alzheimer’s disease also seems to exist in another direction. So the longer nap is obviously not just an indicator that someone might be suffering from Alzheimer’s disease. It also indicates an increased risk of contracting the disease in people who are still healthy.
The scientists compared data from subjects who developed Alzheimer’s disease within six years with data from subjects who remained mentally healthy. It was noted that study participants who slept more than an hour a day had a 40% higher risk of developing this form of dementia than people whose daily nap time was less than an hour. In addition to sleep duration, frequency also seems to play a role. Those who take a nap every day also have a 40% higher risk of developing Alzheimer’s disease than people who don’t close their eyes for a nap every day.
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Could changes in the brain be causing this?
The current study cannot provide an explanation for the results. Nor does it prove that the relationship is causal. So whether longer periods of sleep during the day trigger Alzheimer’s disease or vice versa, which Alzheimer’s disease is responsible – and in what way – when naps become more frequent and last longer.
But researchers believe a previous study from 2019 cites a reason why daytime sleep and Alzheimer’s disease are correlated. This study compared the brains of people who died with and without Alzheimer’s disease. The latter contained, among other things, fewer arousal neurons in three regions of the brain.3
“It is plausible that the associations we observed between excessive daytime naps at baseline and increased risk of Alzheimer’s disease during follow-up may reflect the impact of Alzheimer’s pathology in the preclinical stages,” they said. the study authors, co-led by Yue Leng. , a professor in the Department of Psychiatry and Behavioral Sciences at UCSF.
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Although it cannot (yet) be said with certainty that napping leads to mental decline and thus Alzheimer’s disease, the researchers consider the results of the study to be very remarkable. According to Leng, the study shows for the first time that daytime napping and Alzheimer’s disease “appear to drive mutual changes in a bidirectional fashion.” In addition, the data collected indicates that prolonged napping could be a recognizable warning signal. “It would be very interesting to investigate in future studies whether taking a nap can help slow down age-related cognitive decline,” says Leng.
- 1. Leng Y, Li P, Gao L et al. (2022). Daytime napping and Alzheimer’s dementia: a potential bidirectional relationship. Alzheimer’s and dementia.
- 2. Leigh, S. (2022). Prolonged napping in the elderly can signal dementia. University of California at San Francisco.
- 3. Oh, J., Eser, RA, Ehrenberg, AJ et al. (2019). Profound degeneration of neurons promoting wakefulness in Alzheimer’s disease. Alzheimer’s and dementia.