Researchers found that excessive daytime napping predicts an increased future risk of Alzheimer’s dementia. And, once dementia or its usual precursor – mild cognitive impairment – are diagnosed, the frequency and/or duration of napping accelerates rapidly.
The results were published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association.
“Daytime sleep behaviors of older adults are oftentimes ignored, and a consensus for daytime napping in clinical practice and health care is still lacking,” says co-first author Dr Peng Li, based at the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital in Massachussets, US.
“Our results not only suggest that excessive daytime napping may signal an elevated risk of Alzheimer’s dementia, but they also show that faster yearly increase in daytime napping may be a sign of deteriorating or unfavored clinical progression of the disease,” adds Li.
The study tracked data from 1,401 seniors for up to 14 years. Those studied, approximately three-quarters of whom were female, had an average age of 81 years. They wore watch-like devices that tracked mobility continuously for up to 14 days every year. Each prolonged period without activity detected by the device between 9am and 7pm was interpreted as a nap.
In addition, they underwent yearly neuropsychological tests to evaluate cognition. At the start of the study 75.7% of participants had no cognitive impairment, while 19.5% had mild impairment and 4.1% had Alzheimer’s disease.
The researchers found that longer and more frequent daytime naps were a risk factor for developing dementia in cognitively normal older men and women. As the disease progressed, annual increases in the duration and frequency of napping accelerated – especially after the clinical manifestation of Alzheimer’s dementia.
This occurred independent of known risk factors for dementia – including age and night-time sleep duration and fragmentation.
“We found the association between excessive daytime napping and dementia remained after adjusting for night-time quantity and quality of sleep,” says co-senior author Dr Yue Leng of the University of California San Francisco. “This suggested that the role of daytime napping is important itself and is independent of night-time sleep.”
This increase in napping may be explained by a 2019 study, which compared the post-mortem brains of people with Alzheimer’s disease to those without cognitive impairment and found they had fewer wake-promoting neurons in three brain regions.
The authors acknowledge the limitation that, because the study participants were older, the findings may not easily translate to younger cohort. They also suggest that future studies should test whether a direct intervention in daytime napping can lower the risk of Alzheimer’s dementia or cognitive decline.
“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,” says Leng. “It would be very interesting for future studies to explore whether intervention of naps may help slow down age-related cognitive decline.”
“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,” adds co-senior author Dr Kun Hu, also of Brigham and Women’s Hospital.