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Longer Daytime Naps may be an Early Sign of Dementia

Monday, May 9th, 2022

Many of us have that older uncle who falls asleep on the couch after lunch. It is largely innocuous, sometimes amusing, and most certainly common in older age.  However, new research suggests that extensive daytime napping could mean something more[1].

Some of us may swear by “power naps”, and for younger adults, research indeed suggests that napping may be beneficial to cognition[2]. For older adults though, sleep disturbance is a known symptom of Alzheimer’s disease[3].  However, much of this research is based on one-off self-reports, which are typically unreliable in the remembering of when or for how long we napped –particularly if cognitive impairment is present.

An Objective Watch-Like Movement Device

In a recent study from US, 1,401 elders wore a watch-like device that tracked their movement for up to 14 continuous days each year, for 14 years. The average age of participants was 81 years, and three-quarters were female. A specialised algorithm interpreted any extended periods of inactivity during 9am and 7pm as naps. Cognitive assessments were also administered each year. At the study start, 76% of participants had no cognitive impairment, nearly 20% had mild cognitive impairment, and 4% had been diagnosed with Alzheimer’s disease.

Napping for Over an Hour a day a Risk Factor

Daily napping increased among all participants over the years.  However, there were differences between those who developed Alzheimer’s by the study end, and those who did not. Participants who did not develop cognitive impairment had nap durations that averaged 11 extra minutes per year. This rate was doubled to 25 extra minutes per year for those participants with a mild cognitive impairment diagnosis and tripled to 68 extra minutes per year after an Alzheimer’s diagnosis.

More specifically, adults who napped at least once a day for more than an hour, had a 40% higher chance of developing Alzheimer’s than those who did not nap daily or napped less than an hour a day. Deterioration in cognition was also associated with more daytime napping. These findings were unchanged even after factors like daily activities, health, medications, and night-time quantity and quality of sleep, were considered.

A Bi-Directional Association

It could be that napping causes cognitive aging. It could be that excessive daytime napping signals accelerated aging. It could be that neither cause the other, but that both excessive napping and Alzheimer’s disease share an underlying pathological mechanism.

Intentional versus Unplanned Napping

The authors acknowledge that whilst the method of actigraphy they used is validated and widely used in sleep studies, polysomnography is the gold standard for sleep scoring. Also, the study does not capture whether the naps are planned or unplanned. Dozing off unconsciously might have different healthcare implications than intentional napping.

It is too early to say how this research might affect day-to-day patient care, and the findings only relate to older adults, not young or middle-aged adults.  At minimum, the findings call for closer attention to 24-hour sleep patterns in the health monitoring of older adults.