Twenty-four-hour sleepiness, particularly excessive napping, has been associated with a doubled risk of developing dementia, the latest study on disturbed sleep patterns and the disease has found.
Worldwide, more than 55m people have dementia, with 139m predicted to be affected by the condition by 2050, and while many factors may increase the risk of developing dementia, like uncontrolled diabetes, high blood pressure, hearing loss, and tobacco and alcohol use, several studies have suggested that disturbed sleep patterns may contribute as well – but do not agree whether too much or too little sleep has greater impact.
One study found that high or low sleep duration increased risk of cognitive impairment and dementia: another found that short sleep duration in middle age was associated with higher dementia risk.
A third suggests that sleeping more than nine hours a night is associated with neurodegeneration and dementia.
All relied on participant-reported sleep duration, rather than objective measurement of sleep and wakefulness, reports Medical News Today.
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.
Sleep patterns in older women
The study recruited 733 women from the Study of Osteoporotic Fractures (SOF), all at least 65, who could walk without assistance and had not had two hip replacements. The mean age was 82.5 years.
None 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.
They had to attend the clinic in person, and have at least three consecutive days of actigraph measurements at both initial visit and five-year follow-up, as well as complete a sleep log.
The researchers recorded five-year changes in night-time sleep, napping and circadian rest-activity rhythms (RARs – magnitude, timing and regularity of rest-activity patterns).
They identified three main sleep profiles:
1. stable sleep (SS), seen in 321 women (43.8% of the cohort), was characterised by stable or slightly improved sleep;
2. declining night-time sleep (DNS) – 256 women (34.9%) had decreases in night-time sleep quality and duration, moderate increases in napping, and worsening circadian RARs, and
3. increasing sleepiness (IS) – these 156 women (21.3%) had large increases in both daytime and night-time sleep duration and quality, as well as worsening circadian RARs.
Increased sleepiness
At the end of the five-year period, researchers determined whether participants had normal cognition, mild cognitive impairment (MCI), or dementia, based on a number of neuropsychological tests, physician diagnosis, or admission to residential nursing home care.
Anyone negative for all these criteria was judged to be cognitively normal. 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 five-year follow-up.
Those with increasing 24-hour sleepiness had double the dementia risk of those with stable sleep profiles over the five years. However, increased sleepiness was not associated with increased risk of MCI.
The researchers emphasise 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.”
Why might more sleep raise dementia risk?
“Increased sleepiness and frequent napping may be linked to dementia due to several underlying factors,” Allder said. “One key reason is sleep fragmentation and neurodegeneration – poor night-time sleep quality can disrupt deep sleep, which is essential for clearing amyloid-beta, a protein associated with Alzheimer’s.
“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.”
Allder added that excessive sleepiness might act as a compensatory mechanism for brain dysfunction.
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, said “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”.
He said sleep disturbances could, indeed, signal early neurodegenerative changes, acting as precursors to clinical symptoms, but conversely, dementia-related neurological changes might disrupt the brain’s sleep-regulating centres, exacerbating sleepiness.
Beyond sleepiness alone, “disruptions like fragmented sleep, reduced sleep efficiency, and irregular circadian rhythms are strongly linked to dementia risk”.
“Crucially, sleep-related changes could be used to predict later life dementia risk.”
Study details
Five-Year Changes in 24-Hour Sleep-Wake Activity and Dementia Risk in Oldest Old Women
Sasha Milton, Clémence Cavaillès, Sonia Ancoli-Israel et al.
Published in Neurology on 22 April 2025
Abstract
Background and Objectives
Sleep disruptions are associated with cognitive ageing in older adults. However, little is known about longitudinal sleep changes in the oldest old and whether these changes are linked to cognitive impairment. We aimed to determine whether changes in 24-hour multidimensional sleep-wake activity are associated with mild cognitive impairment (MCI) and dementia in oldest old women.
Methods
We studied cognitively unimpaired women enrolled in the Study of Osteoporotic Fractures who completed wrist actigraphy twice (baseline and follow-up) and had cognitive status evaluated at follow-up using a neuropsychological battery and adjudication. To identify multidimensional sleep-wake change profiles, we performed hierarchical clustering on principal components on the 5-year changes (median 5.0 [range 3.5–6.3] years) in nighttime sleep (sleep duration, sleep efficiency [SE], and wake after sleep onset [WASO]), napping (duration and frequency), and circadian rest-activity rhythms (RARs; acrophase, amplitude, mesor, and robustness). Using multinomial logistic regression, we evaluated the associations between these profiles—and individual parameter changes—and MCI and dementia risk at follow-up.
Results
Of 733 participants (mean age 82.5 ± 2.9 years), 164 (22.4%) developed MCI and 93 (12.7%) developed dementia by the follow-up visit. We identified 3 sleep-wake change profiles: stable sleep (SS; n = 321 [43.8%]) was characterised by stability or small improvements; declining nighttime sleep (n = 256 [34.9%]) showed decreases in nighttime sleep quality and duration, moderate napping increases, and worsening circadian RARs; and increasing sleepiness (IS; n = 156 [21.3%]) exhibited large increases in daytime and nighttime sleep duration and quality, and worsening circadian RARs. After adjustment for age, education, race, body mass index, diabetes, hypertension, myocardial infarction, antidepressant use, and baseline cognition, women with IS had approximately double the risk of dementia (odds ratio 2.21, 95% CI 1.14–4.26) compared with those with SS. SE, WASO, nap duration, and nap frequency were individually associated with dementia. Neither sleep-wake change profiles nor individual parameters were associated with MCI.
Discussion
Among community-dwelling women in their 80s, those with increasing 24-hour sleepiness over five years had doubled dementia risk during that time. Change in multidimensional 24-hour sleep-wake activity may serve as an early marker or risk factor for dementia in older women.
See more from MedicalBrief archives:
Seven hours is ideal amount of sleep in middle-age and older – UK-China study
Impaired sleep linked to accumulation of Alzheimer’s marker
Sleep duration as risk factors for dementia and premature death
Day-time sleepiness linked to Alzheimer’s risk