Is excessive sleepiness a warning sign of dementia?

 

According to the World Health Organization (WHO), “Dementia is currently the seventh leading cause of death among all diseases and one of the major causes of disability and dependency among older people globally.”

The WHO states that around 55 million people have dementia, and the number is increasing by about 10 million every year. and by 2050 the number is likely to be almost 140 million. Between 60% and 70% of people with dementia have Alzheimer's disease.

Dementia is primarily a disease of old age. Many factors may increase a person’s risk of developing dementia such as:

• lack of physical activity
• uncontrolled diabetes
• high blood pressure (hypertension)
• hearing loss
• tobacco and alcohol use.

There is also a genetic component to dementia. However, several studies have shown that even those with a hereditary risk can reduce it by adopting a healthy diet, exercising regularly, and avoiding smoking and too much alcohol.

Another healthy lifestyle is getting enough of the right sort of sleep. And many researchers are now seeing connections between sleep and dementia.

Dr. David Merrill, geriatric psychiatrist, said, “Sleep is a factor that can either be protective or risky for cognitive health. The effects of sleep on cognitive health depend on the attributes of an individual’s sleep, including the quality, quantity, frequency and even the regularity of sleep.”

A new study in women over 80 years of age has linked increased sleepiness with greater dementia risk. It was found that 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 (mild cognitive impairment).

The study appears in the journal Neurology.

Ben Dunkley, a cognitive neuroscientist, 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.”

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.”

Steve Allder, MDm consultant neurologist said:

“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. 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 said.

He further advised, “Improving sleep quality through lifestyle modifications — such as consistent sleep schedules, minimizing alcohol consumption, and optimizing sleep hygiene — can measurably enhance brain health.”

“It’s recommended — not only for brain health, but for overall health — that people get 7 to 9 hours of quality sleep per night.”

Those who regularly slept for more than 9 hours a night had double the dementia risk of those who slept between 6 and 9 hours, according to a large-cohort study from Boston University. They also had lower brain volumes.

It may be that excessive sleep was a symptom of early neuronal changes rather than the cause. The researchers of this study suggest that long sleep time could be a predictor of dementia risk.

Meanwhile, if sleep is disturbed, brain waste, such as beta-amyloid and tau, may start to build up, eventually forming the plaques and tangles characteristic of Alzheimer’s. Accumulation of beta-amyloid and tau may begin 10-20 years before dementia symptoms become noticeable.

“The disrupted, poor-quality sleep seen in sleep disorders leads to both acute and chronically worsening changes in the brain. Normally, a good night’s sleep literally allows for repair and restoration of brain function to the levels seen at the beginning of the prior day.”

Dr. Porsteinsson explained: “When you sleep, the brain ‘shrinks’ which appears to open up the flow of cerebrospinal fluid that flushes out toxic byproducts such as beta-amyloid and p-tau. The brain also resets its balance (homeostasis) during sleep. The quality of sleep and how much time you spend in deep-sleep matters here as well.”

Moreover, people with sleep apnea are at increased risk of several health conditions. Recent studies have also suggested the links between sleep apnea and dementia.

One study found that the temporal lobes — which are vital for memory — were reduced in thickness in those with sleep apnea, a change that is also seen in people with dementia.

Another study found that the hippocampus was reduced in volume in people with sleep apnea — hippocampal atrophy is a feature of Alzheimer’s disease.

This study also showed that two toxins — tau and beta-amyloid, which are thought to be responsible for many of the symptoms of dementia — build up in the brains of people with sleep apnea, probably because of a lack of oxygen in the blood.

Two more studies added to these findings. One detected raised tau levels in those with sleep apnea; the other found them to have amyloid plaques.

A 2019 review of studies found that sleep disorders, including sleep apnea, insomnia, inadequate or overlong sleep, and sleep disturbance were linked to cognitive decline and dementia.

Maintaining a healthy lifestyle and ensuring you get enough quality sleep may reduce the risk of both dementia and many other health problems. Thus improving sleep might be a way of alleviating dementia symptoms.

But no study has yet proved a causative link — or which way the relationship acted. Did sleep problems predispose to dementia, or were sleep problems a sign of the early stages of dementia? Is it possible that treating sleep disorders might help prevent dementia?