MINNEAPOLIS — For women in their 80s, experiencing increasing sleepiness during the day over a five-year period is associated with double the risk of developing dementia during that time, according to a study published on March 19, 2025, online in Neurology® , the medical journal of the American Academy of Neurology . The study does not prove that daytime sleepiness causes dementia; it only shows an association.
"Sleep is essential for cognitive health, as it allows the brain to rest and rejuvenate, enhancing our ability to think clearly and remember information," said study author Yue Leng, PhD, of the University of California, San Francisco. "However, little is known about how changes in sleep and cognition are connected over time and how these changes relate to dementia risk in the later decades of life. Our study found that sleep problems may be intertwined with cognitive aging and may serve as an early marker or risk factor for dementia in women in their 80s."
For the study, researchers looked at 733 female participants with an average age of 83 who did not have mild cognitive impairment or dementia at the start of the study. They were followed over five years.
During the study, 164 participants, or 22%, developed mild cognitive impairment and 93 participants, or 13%, developed dementia.
Participants wore wrist devices to track their sleep and circadian rhythm patterns for three days at the start and end of the study.
Researchers looked at the changes in nighttime sleep duration and quality, daytime napping and circadian rhythm patterns.
After five years, researchers observed large changes in sleep patterns in more than half of the participants, or 56%.
Researchers found that participants fell into three groups: stable sleep or small improvements in sleep, 44%; declining nighttime sleep, 35%; and increasing sleepiness, 21%. Declining nighttime sleep included decreases in nighttime sleep quality and duration, moderate increases in napping and worsening circadian rhythms. Increasing sleepiness included increases in both daytime and nighttime sleep duration and quality, along with worsening circadian rhythms.
Researchers then looked at how these changes were linked to the risk of developing dementia.
Of those in the stable sleep group, 25, or 8%, developed dementia. In the declining nighttime sleep group, 39, or 15%, developed dementia. In the increasing sleepiness group, 29, or 19%, developed dementia.
After adjusting for age, education and race, and health factors such as diabetes and high blood pressure, researchers found that participants in the increasing sleepiness group had double the risk of dementia compared to those in the stable sleep group. No association was found in the declining nighttime sleep group.
"We observed that sleeping, napping and circadian rhythms can change dramatically over only five years for women in their 80s," Leng said. "This highlights the need for future studies to look at all aspects of daily sleep patterns to better understand how changes in these patterns over time can be linked to dementia risk."
A limitation of the study was that it included primarily white people, so the results cannot be generalized to more diverse populations.
The study was funded by the National Institutes of Health and the National Institute on Aging.
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