In a new cohort study, published in the journal Alzheimer’s & Dementia, participants tended to nap longer and more frequently with aging; most importantly, the progression of Alzheimer’s dementia appeared to accelerate this aging effect by doubling or more than doubling the annual changes (increases) in nap duration/frequency; the study’s results also show that longer and more frequent daytime naps were associated with higher risk of developing Alzheimer’s dementia.
Daytime napping and cognition may drive each other’s changes bidirectionally. Image credit: StockSnap.
Excessive daytime napping is frequently seen in older adults, especially in those with Alzheimer’s disease.
A recently proposed mechanism is the arousal deficiency due to neuronal and neurotransmitter loss in wake-promoting neurons associated with tau tangles, one of the pathological hallmarks of Alzheimer’s disease, resulting in sleep-wake disturbances and a higher propensity for daytime napping.
The other way around, excessive sleepiness during daytime, which may be a cause of longer and frequent naps, has also been linked to faster cognitive decline or Alzheimer’s disease pathology build-up.
However, there remain conflicting results regarding the effects of daytime napping on cognition in prior research.
Whereas some studies have shown that daytime napping has benefits on acute cognitive performance, mood, and alertness, other studies have highlighted the adverse outcomes on cognitive performance.
Nevertheless, Dr. Peng Li of Brigham and Women’s Hospital and colleagues recognized that all prior studies on Alzheimer’s disease assessed napping within a participant only once, and most of them were subjective and questionnaire based.
They tested two hypotheses: (i) participants nap longer and/or more frequently with aging and the changes are even faster with the progression of Alzheimer’s disease; and (ii) participants with excessive daytime napping are at an increased risk of developing Alzheimer’s disease.
“Daytime sleep behaviors of older adults are oftentimes ignored, and a consensus for daytime napping in clinical practice and health care is still lacking,” Dr. Li said.
“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.”
“Our study calls for a closer attention to 24-hour sleep patterns — not only nighttime sleep but also daytime sleep — for health monitoring in older adults.”
Dr. Li and co-authors used data from the ongoing Rush Memory and Aging Project (MAP), a prospective, observational cohort study conducted at the Rush Alzheimer’s Disease Center.
A total of 1,401 individuals, with an average age of 81, were provided a watch-like device called Actical (Philips Respironics) to wear on their non-dominant wrist for up to 14 days.
The researchers identified sleep episodes using a previously validated sleep scoring algorithm that considers wrist activity counts.
After napping episodes were identified, the nap duration and frequency were calculated.
The authors learned that nap duration and nap frequency were positively correlated with age and found a bidirectional, longitudinal relationship between daytime sleep and Alzheimer’s.
Independent of known risk factors for dementia, including age and nighttime sleep duration and fragmentation, longer and more frequent daytime naps were a risk factor for developing Alzheimer’s in cognitively normal older men and women.
Besides, annual increases in napping duration and frequency were accelerated as the disease progressed, especially after the clinical manifestation of Alzheimer’s.
Ultimately, the scientists describe the relationship between daytime napping and cognition to be a ‘vicious cycle.’
“The vicious cycle we observed between daytime sleep and Alzheimer’s disease offers a basis for better understanding the role of sleep in the development and progression of Alzheimer’s disease in older adults,” Dr. Li said.
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Peng Li et al. Daytime napping and Alzheimer’s dementia: A potential bidirectional relationship. Alzheimer’s & Dementia, published online March 17, 2022; doi: 10.1002/alz.12636
