A recent study published on March 19, 2025, in Neurology®, the medical journal of the American Academy of Neurology, presents findings highlighting a significant correlation between increasing daytime sleepiness over five years and a doubled risk of developing dementia among women in their 80s. This study, while insightful, clarifies that it does not establish daytime sleepiness as a causative factor for dementia but instead underscores a notable association between the two conditions.
Dr. Yue Leng, PhD, from the University of California, San Francisco, and the study’s principal investigator, underscores the critical role that sleep plays in cognitive health. He notes that adequate sleep is essential for the brain’s rest and rejuvenation, supporting clear thinking and effective memory retention. Despite these findings, Dr. Leng points out that the dynamics between changes in sleep patterns and cognitive functions, particularly their impact on dementia risk in later years, remain poorly understood. The study suggests that disturbances in sleep may be intricately linked with cognitive ageing and could potentially act as early markers for dementia risk among older women.
Throughout the study, researchers monitored 733 women, averaging 83 years old, none of whom had mild cognitive impairment or dementia at the beginning. Over the following five years, the health outcomes were significant: 164 women developed mild cognitive impairment, and 93 were diagnosed with dementia, translating to 22% and 13% of the study population, respectively.
The methodology involved participants wearing wrist devices to track their sleep and circadian rhythms for three days at the start and the end of the study period. The researchers examined nighttime sleep quality and duration changes, daytime napping habits, and circadian rhythm patterns. By the end of the study, over half the participants (56%) exhibited significant changes in their sleep patterns.
These participants were categorized into three groups based on their sleep changes: those whose sleep remained stable or slightly improved made up 44%; those with declining nighttime sleep accounted for 35%; and those experiencing increased sleepiness formed 21%. Notably, the declining nighttime group showed reduced sleep quality and duration, increased daytime napping, and worsening circadian rhythms. In contrast, the group with increased sleepiness experienced improved daytime and nighttime sleep quality and duration, though their circadian rhythms also deteriorated.
Further analysis showed distinct differences in dementia risk across these groups. In the stable sleep group, only 8% developed dementia; this rose to 15% in the declining nighttime sleep group and to 19% in the increasing sleepiness group. After adjusting for various factors such as age, education, race, and health conditions like diabetes and high blood pressure, the researchers found that those in the increasing sleepiness group faced double the risk of developing dementia compared to those in the stable sleep group. No significant link was found in the declining nighttime sleep group. Dr Leng emphasized the rapid changes observed in sleep patterns over just five years and highlighted the need for comprehensive future studies that examine all aspects of sleep to understand its connection to dementia risk better. However, a limitation of the study is its predominantly white cohort, suggesting the findings may not be generalizable across more diverse populations. This limitation underscores the necessity for further research involving a broader demographic to ascertain the full implications of sleep patterns on dementia risk.
More information: Yue Leng et al, Five-Year Changes in 24-Hour Sleep-Wake Activity and Dementia Risk in Oldest Old Women, Neurology. DOI: 10.1212/WNL.0000000000213403
Journal information: Neurology Provided by American Academy of Neurology
