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“While sleep is considered to enhance memory retention and consolidation, especially among healthy younger adults, it remains controversial whether napping could benefit cognition by compensating for poor nighttime sleep, or if napping might be a … risk factor of cognitive impairment in the elderly,” wrote Yue Leng, Ph.D., M.Phil., of the University of California, San Francisco, and colleagues.
Leng and colleagues measured naps in 2,751 men aged 65 years and older who were enrolled in the Osteoporotic Fractures in Men Study between 2000 and 2002. The participants wore devices similar to wristwatches that measured sleep-wake activity for at least five days in a row when they first enrolled in the study, then had at least one follow-up visit over the next 12 years in which researchers measured their cognitive function.
The researchers found that men who napped for at least two hours during the day at baseline were 66% more likely to develop cognitive impairment than those who napped for fewer than 30 minutes. When the researchers included data on how well and how long the participants slept at night, they found that the so-called “long nappers” who also slept soundly or for six to eight hours a night had roughly twice the risk of developing cognitive impairment compared with their counterparts whose naps were shorter than 30 minutes. However, longer naps were not associated with a higher risk of cognitive decline among participants who did not sleep well at night or who only slept a few hours a night.
“This indicates that the effects of napping on cognition are different among those who sleep poorly and those who sleep well at night,” Leng and colleagues wrote. “Napping might help compensate for poor nighttime sleep and thus provide extra benefits on cognition among those who sleep poorly at night. Meanwhile, it is unclear why napping might be associated with increased risk of cognitive impairment among those who sleep well at night.”
Because the study included only men and most participants were white, the researchers cautioned the findings may not be generalizable to women and/or people of other ethnicities. They concluded that excessive napping could be either an early sign or a risk factor of cognitive decline, and they encouraged health professionals to pay attention to 24-hour sleep-wake cycles of older patients.
For related information, see the Psychiatric News article “Sleep Loss Found to Exacerbate Spread of Toxic Protein Associated With Alzheimer’s Disease.”
(Image: iStock/Dean Mitchell)
