For older adults, both excessive and insufficient sleep have been linked to cognitive problems.
Not getting enough sleep in later life is linked to a higher risk of developing Alzheimer’s disease. However, getting too much sleep can also be a risk factor.
Scientists agree there is a link between sleep and dementia, but the exact nature of this relationship is complex. Poor sleep might trigger brain changes that lead to dementia, or existing health issues that affect the brain might also disrupt sleep. Additionally, changes in sleep patterns can be an early indicator of dementia.
Here’s how experts view these connections and how you can assess your risk based on your sleep habits.
Too Little Sleep
Sleep functions like a nightly cleansing process for the brain, clearing out the cellular waste that builds up during the day. This process involves the fluid around brain cells flushing out molecular debris into the bloodstream, where it is filtered by the liver and kidneys and then removed from the body.
This cellular waste includes the protein amyloid, which is believed to play a crucial role in Alzheimer’s disease. Everyone produces amyloid throughout the day, but issues arise when it accumulates into sticky clumps called plaques. The longer someone stays awake, the more amyloid builds up, leaving less time for the brain to clear it out.
Scientists aren’t certain whether consistently getting too little sleep—typically six hours or less per night—alone can trigger amyloid accumulation. However, research has shown that among adults aged 65 to 85 who already have plaques in their brains, those who slept less had more amyloid build-up and poorer cognitive function.
“Is lack of sleep sufficient to cause dementia? Probably not on its own,” said Dr. Sudha Seshadri, the founding director of the Glenn Biggs Institute for Alzheimer’s and Neurodegenerative Diseases at the University of Texas Health Science Center at San Antonio. “But it certainly seems to be a risk factor that increases the likelihood of dementia and may accelerate cognitive decline.”
While Alzheimer’s disease symptoms typically appear in one’s 60s or 70s, amyloid accumulation can start up to two decades earlier. Therefore, prioritizing sleep—aiming for seven to nine hours per night—is essential, starting in your 40s or 50s, if not sooner, advised Joe Winer, a postdoctoral fellow in neurology and neurological sciences at the Center for Sleep and Circadian Sciences at Stanford University.
“We don’t have a definitive answer on whether sleep patterns in your 20s impact late-life dementia risk,” Dr. Winer said. “But evidence suggests that sleep quality becomes increasingly important as you approach midlife and beyond, particularly in your 60s and 70s.”
The Impact of Sleep Disorders and Excessive Sleep on Dementia Risk
Certain sleep disorders, particularly sleep apnea, are associated with an increased risk of dementia. Sleep apnea, which disrupts sleep, is often found in individuals who are overweight or have diabetes—conditions that are also linked to dementia. However, even after accounting for these factors, sleep apnea itself seems to independently increase the risk of dementia. Dr. Diego Carvalho, an assistant professor of neurology at the Mayo Clinic’s Center for Sleep Medicine, explains that sleep apnea can limit the brain’s oxygen supply, leading to increased brain inflammation and damage to blood vessels and cells.
Too Much Sleep
On the opposite end of the spectrum, excessive sleep is also linked to a higher risk of dementia, though perhaps more indirectly. Regularly staying in bed for more than nine hours a night or taking multiple naps during the day may indicate poor sleep quality, which can increase Alzheimer’s risk for the reasons previously mentioned.
Excessive sleep may also be related to mental or physical health issues. Mental health conditions like depression and physical health problems such as diabetes or cardiovascular issues are linked to a higher dementia risk. Additionally, factors like physical inactivity, loneliness, and isolation are associated with dementia.
“At this point, there’s no clear causative role of long sleep in relationship to dementia,” Dr. Carvalho said. “It may be more like a symptom of an underlying problem than the cause of the problem.”
An Early Symptom?
One of the early signs of Alzheimer’s disease might be disruptions in sleep patterns. The regions of the brain that regulate sleep and circadian rhythms are among the first affected by Alzheimer’s. Consequently, individuals developing the condition may experience sleep issues even before noticeable memory loss or other symptoms arise.
Besides amyloid, the protein tau is also believed to play a critical role in Alzheimer’s disease. Similar to amyloid, tau accumulates in the brain and damages brain cells. One of the initial areas where tau buildup appears is the brainstem regions responsible for regulating sleep and wakefulness, according to Dr. Winer. “We think that tau showing up in these areas very early on is going to disrupt people’s sleep-wake cycles,” Dr. Winer said.
Sleep disturbances can also be an early indicator of other common types of dementia. For instance, in Lewy body dementia and Parkinson’s disease dementia, rapid eye movement (REM) sleep may be disrupted, leading individuals to act out their dreams—a phenomenon often noticed by bed partners, as Dr. Seshadri noted.
“Normally, during rapid eye movement sleep, muscle tone decreases to nearly zero, preventing muscle movement,” Dr. Seshadri explained. “In REM behavior disorder, this suppression of muscle tone is lost, causing individuals to physically act out their dreams.”.
When to Seek Help for Sleep Changes in Older Adults
Experts agree that it’s normal for older adults to experience slight changes in their sleep patterns after retirement. It’s common to sleep a bit more or less, or to have altered bedtimes and wake times. However, significant shifts in sleep habits might indicate a need for medical attention.
“If someone is waking up at 2 a.m. or 3 a.m., or sleeping for three hours during the day, that’s a cause for concern,” said Dr. Seshadri. “In contrast, getting up an hour earlier than usual and taking a 30 to 60-minute nap during the day is much more likely to be a part of normal aging.”
If you notice dramatic changes in your sleep patterns, it may be wise to consult your doctor or a sleep specialist. They can help determine if these changes are a sign of a more serious issue or just a natural part of getting older..
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