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Longer, more frequent daytime naps in elderly adults predicted a higher risk of incident Alzheimer's dementia over time, an actigraphy study showed.

Elderly people who napped more than once a day had 1.3-fold increased risk in developing future Alzheimer's dementia, reported Peng Li, PhD, of Brigham and Women's Hospital in Boston, and colleagues, at the virtual SLEEP 2020, a joint meeting of the American Academy of Sleep Medicine and the Sleep Research Society.

"Importantly, these associations were independent from depressive symptoms, vascular diseases, and risk factors, and prescribed medications that may all contribute to sleep," Li said.

Studies have shown conflicting messages about links between daytime napping and cognition, he noted. "Some research provided evidence that a short, planned nap may improve cognitive performance, while the others suggested that excessive self-reported daytime napping may be tied to cognitive impairment or more cognitive decline," Li told MedPage Today.

"Using a longitudinal design and objective measures of daytime napping based on ambulatory actigraphy, this study for the first time showed that longer and more frequent daytime naps were associated with increased future risk of Alzheimer's dementia," he said.

The study involved 1,180 people with an average age of 81 from the . No participant had dementia at baseline, but 264 people had mild cognitive impairment.

At baseline, motor activities were recorded with wrist actigraphy for up to 10 days to assess napping characteristics objectively. The researchers defined daytime napping episodes as motor activity segments between 10 a.m. and 7 p.m. with continuous zero activity for 10 minutes or more but less than 1 hour (to avoid off-wrist periods). Segments that were less than 5 minutes apart were merged.

On average, participants napped for 38.3 minutes and 1.56 times a day at baseline. In total, 277 participants developed Alzheimer's dementia within 5.74 years.

Every 30-minute increase in daily napping duration was associated with a 20% increase in the risk of incident Alzheimer's dementia (95% CI 9%-31%, P=0.0002), after adjusting for age, sex, and education. One more nap per day was associated with a 19% increase in the risk of Alzheimer's dementia (95% CI 8%-30%, P=0.0003). These associations remained even after adjusting for total sleep time.

"One of the unique settings of this study is that participants were followed annually with not only clinical assessments, but also motor activity monitoring that allowed objective measurement of daytime napping behavior," Li pointed out.

Compared with objective activity assessments, self-reports are highly subjective and may suffer from recall bias, he noted: "So-called 'snoozes' or periods of drowsiness are more likely to be detected by objective algorithm, but left out during self-report."

In other research presented at the SLEEP meeting, Li and colleagues reported within-person changes in daytime napping. "We found that objective daytime napping became longer and more frequent over time within individuals," he said.

"Importantly, the speed of napping prolongation was accelerated after the diagnosis of mild cognitive impairment, and further after the diagnosis of Alzheimer's dementia," Li said. "Altogether, our studies demonstrated a potential bidirectional relationship between daytime napping and Alzheimer's dementia."

Study participants had an average baseline age of about 80, and how napping at younger ages relates to late-life cognitive performance, decline, or dementia warrants further study, he added.

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