Sleepier During the Day? It May Double Your Dementia Risk

A new study found that women in their 80s who experience increasing daytime sleepiness over five years have double the risk of developing dementia.

While the study doesn’t prove that excessive sleep causes dementia, it highlights a strong connection between sleep changes and cognitive decline.

Increasing Daytime Sleepiness Linked to Dementia Risk

Women in their 80s who become increasingly sleepy during the day over a five-year period may face twice the risk of developing dementia, according to a study published today (March 19, 2025) in Neurology, the medical journal of the American Academy of Neurology. However, the study does not confirm that daytime sleepiness causes dementia, only that the two are linked.

“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.”

Tracking Sleep Patterns in Aging Women

The study followed 733 women with an average age of 83, all of whom had no signs of mild cognitive impairment or dementia at the start. Over five years, researchers tracked their cognitive health and found that 164 participants (22%) developed mild cognitive impairment, while 93 (13%) were diagnosed with 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.

How Sleep Changes Over Five Years

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.

The Link Between Sleep and Dementia Risk

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 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.”

Limitations of the Study

A limitation of the study was that it included primarily white people, so the results cannot be generalized to more diverse populations.

Reference: “Five-Year Changes in 24-Hour Sleep-Wake Activity and Dementia Risk in Oldest Old Women” by Sasha Milton, Clémence Cavaillès, Sonia Ancoli-Israel, Katie L. Stone, Kristine Yaffe and Yue Leng, 19 March 2025, Neurology.

The study was funded by the National Institutes of Health and the National Institute on Aging.