Excessive napping may be an early warning sign of age-related cognitive decline in older men, according to a 12-year study by UC San Francisco scientists.
The researchers used wrist-mounted sensors to track sleep–wake habits over five days in nearly 3,000 men over the age of 65 living in community housing situations, then followed-up with cognitive assessments over the subsequent years.
The authors previously reported that men who napped for more than an hour a day at the beginning of the study were two to three times more likely to develop Parkinson's disease within 11 years. Now, a study published June 18, 2019 in Alzheimer's & Dementia extends those results to suggest that napping may also precede the risk of dementia and cognitive decline more broadly.
The study found that men who had napped for an average of two hours or more per day at the beginning of the study were 66 percent more likely to develop clinically significant cognitive impairment than men who had only napped for 30 minutes or less a day. Excessive napping was most strongly linked to later cognitive impairment in men who slept well at night, suggesting that night-time sleep disruption was unlikely to directly explain the relationship, though more subtle interactions could not be ruled out.
Prior studies have suggested a connection between napping and age-related cognitive decline and dementia, but most have relied on retrospective self-reports, which are not very reliable, and none have tracked the consequences of objectively measured 24-hour sleep patterns over such a long period.
“There has been increasing evidence that nighttime sleep disturbances might be a risk factor for dementia, but the role of daytime napping has always been controversial,” said study lead author Yue Leng, PhD, a former postdoctoral scholar who has recently accepted a position as an assistant professor of psychiatry at UCSF. “For the first time, we can clearly show an association between objectively measured naps and long-term risk of cognitive decline.”
Leng and study senior author Kristine Yaffe, MD, who is Roy and Marie Scola Endowed Chair and Vice Chair of Research in Psychiatry at UCSF, previously published data showing that older adults with dementia were three times more likely to nap during the day than those without dementia. The new study suggests the relationship may go both ways: people with cognitive impairments may nap more, and people who nap more be at higher risk of later cognitive decline.
More research is needed, the authors say, to understand the biological mechanisms linking sleep with age-related cognitive decline, and whether napping is merely an early warning sign of cognitive decline or could actually contribute to dementia.
“The results suggest that clinicians should pay close attention to 24-hour sleep patterns in older adults,” Yaffe said.
“Whether or not excessive napping actually contributes to cognitive decline,” added Leng, “it is a clearly observable behavior that might be useful as a preclinical marker to predict who is at greater risk of developing dementia down the line.”