- At least 55 million people are living with dementia worldwide, and numbers are increasing rapidly.
- Studies have suggested links between altered sleep patterns and dementia risk.
- A new study in women over 80 years of age has linked increased sleepiness with greater dementia risk.
- Women with increased sleepiness were twice as likely to develop dementia during the 5-year study as those with stable sleep patterns.
Dementia is an increasing problem worldwide. More than 55 million people are currently living with the condition, with 139 million predicted to have dementia by 2050.
Many factors may increase a person’s risk of developing dementia. According to the Centers for Disease Control and Prevention (CDC),
- lack of physical activity
- uncontrolled diabetes
- high blood pressure (hypertension)
- hearing loss
- tobacco and alcohol use.
Several studies have suggested that disturbed sleep patterns may contribute to dementia risk, but do not agree whether too much or too little sleep has greater impact.
One large-scale study found that high or low sleep duration increased risk of cognitive impairment and dementia.
A third suggests that sleeping more than 9 hours a night is associated with neurodegeneration and dementia.
All these studies relied on participant-reported sleep duration, rather than objective measurement of sleep and wakefulness.
Now, a study led by scientists at the University of California, San Francisco, which used sleep trackers to monitor the sleep patterns of 733 women in their 80s, has found that increased 24-hour sleepiness, particularly excessive napping, was associated with a doubled risk of developing dementia.
The study appears in the journal Neurology.
Ben Dunkley, PhD, a cognitive neuroscientist, associate professor in Medical Imaging at the University of Toronto, Canada, and Chief Science Officer at MYndspan, who was not involved in this research, told Medical News Today that “the study rightly highlights the bidirectional relationship between sleepiness and dementia; however, as the authors point out, the exact direction of the relationship cannot be concluded with a correlation study such as this.”
Dunkley explained that:
“Sleep disturbances could indeed signal early neurodegenerative changes, acting as precursors to clinical symptoms. Conversely, dementia-related neurological changes might disrupt the brain’s sleep-regulating centers, exacerbating sleepiness. Crucially, sleep-related changes could be used to predict later life dementia risk.”
The study recruited 733 community-dwelling women from the
No participants had cognitive impairment or dementia at baseline.
Researchers gave all participants an actigraph, which they wore on their wrists to measure their 24-hour sleep-wake activity.
For their data to be included in the analysis, participants had to attend the clinic in person, and have at least 3 consecutive days of actigraph measurements at both initial visit and five-year follow-up, as well as completing a sleep log.
From the data, researchers recorded 5-year changes in night-time sleep, napping and circadian
They identified three main sleep profiles:
- stable sleep (SS), seen in 321 women (43.8% of the cohort), was characterized by stable or slightly improved sleep
- declining nighttime sleep (DNS) — a total of 256 women (34.9%) had decreases in nighttime sleep quality and duration, moderate increases in napping, and worsening circadian RARs
- increasing sleepiness (IS) — these 156 women (21.3%) had large increases in both daytime and nighttime sleep duration and quality, as well as worsening circadian RARs.
At the end of the 5-year period, researchers determined whether participants had normal cognition,
The researchers adjusted for age, education, race, body mass index, diabetes, hypertension, heart attack, use of antidepressants, and cognitive ability at baseline when analysing their results.
Of the elderly cohort, 164 (22.4%) women developed MCI and 93 (12.7%) developed dementia during the 5-year follow-up.
Women with increasing 24-hour sleepiness had approximately double the dementia risk of those with stable sleep profiles over the 5 years. However, increased sleepiness was not associated with increased risk of MCI.
The researchers emphasize that their observational study cannot show the direction of the relationship between excessive sleep and dementia.
Steve Allder, MDm consultant neurologist at Re:Cognition Health, who was not involved in this study, told MNT that:
“Older adults in the preclinical stages of dementia may experience increased daytime sleep as a response to brain changes affecting arousal and alertness. Neurodegeneration in regions like the hypothalamus and brainstem, which regulate sleep, could result in greater daytime sleep needs. Inflammation and vascular risk may [also] be contributing factors. Disrupted sleep patterns and excessive sleep are linked to increased inflammation and cardiovascular risks, both of which are known to play a role in dementia development.”
“Increased sleepiness and frequent napping may be linked to dementia due to several underlying factors,” Allder told MNT, adding that “one key reason is sleep fragmentation and neurodegeneration — poor nighttime sleep quality can disrupt deep sleep, which is essential for clearing amyloid-beta, a protein associated with Alzheimer’s disease.”
“Circadian disruption also plays a role, as worsening sleep-wake cycles and irregular circadian rhythms are associated with neurodegenerative changes. Circadian misalignment can impair memory consolidation and contribute to cognitive decline,” he continued.
Concurring with the researchers’ suggestion that increased sleepiness might be a result of early dementia, Allder also explained that excessive sleepiness might act as a compensatory mechanism for brain dysfunction.
This study provides further evidence that altered sleep patterns in older age may contribute to the risk of dementia.
Dunkley offered advice for maintaining good sleep patterns.
”Beyond sleepiness alone, disruptions like fragmented sleep, reduced sleep efficiency, and irregular circadian rhythms are strongly linked to dementia risk,” he told us.
His and his colleagues’ experience with people in real-world scenarios, he further advised, ”supports findings that improving sleep quality through lifestyle modifications — such as consistent sleep schedules, minimizing alcohol consumption, and optimizing sleep hygiene — can measurably enhance brain health.”
“Technologies like magnetoencephalography (MEG), combined with lifestyle tracking tools such as wearable sleep monitors, enable individuals to objectively monitor improvements in their sleep and cognitive health,” Dunkley also noted.
