Long naps increase chances of Alzheimer’s disease, study suggests

A recent study headed by Brigham and Women’s Hospital researchers discovered that frequent daytime napping can raise the chance of Alzheimer’s disease in the future, and dementia accelerated the increase in daytime napping during ageing.
The study was published in the journal ‘Alzheimer’s & Dementia: The Alzheimer’s Association Journal.’

“Daytime sleep behaviours of older adults are oftentimes ignored, and a consensus for daytime napping in clinical practice and health care is still lacking,” said Peng Li, PhD, of the Medical Biodynamics Program in the Brigham’s Division of Sleep and Circadian Disorders.

“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 closer attention to 24-hour sleep patterns — not only nighttime sleep but also daytime sleep — for health monitoring in older adults,” he added.

The impact of daytime napping on cognition in older persons yielded contradictory results. While some studies have found that daytime napping improves acute cognitive function, mood, and alertness, others have found that it has a negative impact on cognitive performance.

Nonetheless, Brigham researchers noted that all previous Alzheimer’s disease studies measured napping in a participant just once, and the majority of them were subjective and questionnaire-based. As a result, they intended to perform a long-term, objective examination of naps in order to discover the relationship between daytime napping and Alzheimer’s disease.

The current study put two hypotheses to the test:
1. Participants snooze longer and/or more frequently as they age, and the changes are considerably more rapid as Alzheimer’s disease progresses.
2. Participants who snooze excessively during the day are more likely to acquire Alzheimer’s disease.

The researchers used a previously established sleep scoring system that takes wrist activity counts into account to identify sleep periods. The nap length and frequency were calculated when napping episodes were detected.

Researchers discovered that nap length and frequency were positively connected with age in the unique cohort study, as well as a bi-directional, longitudinal association between daytime sleep and Alzheimer’s dementia. Longer and more frequent daytime naps were a risk factor for acquiring Alzheimer’s dementia in cognitively normal older men and women, independent of recognised dementia risk variables such as age and nocturnal sleep length and fragmentation.

“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,” said Peng Li.

Three major research limitations were mentioned by the authors. First, despite the fact that actigraphy has been widely utilised and verified in sleep field investigations, researchers acknowledged that polysomnography is the gold standard for sleep grading. Second, because the individuals in the study were older, the findings may not be easily transferred to younger cohorts. Third, future research should look at whether a direct intervention in the form of daytime napping might reduce the risk of Alzheimer’s disease or 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,” said co-senior author Kun Hu, PhD, of the Medical Biodynamics Program in the Brigham’s Division of Sleep and Circadian Disorders.

“Sleep changes are critical in shaping the internal changes in the brain related to the circadian clocks, cognitive decline and the risk of dementia,” he concluded.