Good-quality sleep could play a bigger role than sleep duration in protecting brain health in later life, new research suggests.
The study monitored women aged 82 and over who had no signs of cognitive impairment.
Participants were recruited after experiencing fractures linked to osteoporosis and wore wrist-worn actigraphy devices to track their movement, sleep and wake cycles.
Researchers identified three patterns of sleep-wake changes: stable sleep, declining night-time sleep, and increasing sleepiness.
Women in the increasing sleepiness group—who had large increases in both daytime and night-time sleep—had twice the risk of developing dementia compared to those with stable sleep patterns.
Dr Amy Amara, professor of neurology at the University of Colorado School of Medicine, was not involved in the study but has researched sleep and neurodegeneration extensively.
She said the findings highlight the complex and often circular relationship between sleep and cognitive health.
Dr Amara said: “We know that in neurodegenerative disease, brain changes happen long before we detect any clinical symptoms,.
“The question is whether those changes disrupt sleep, or if sleep disruption contributes to the disease—it’s a chicken-and-egg situation.”
Growing evidence suggests both can be true, with poor sleep potentially fuelling neurodegeneration and vice versa—creating what researchers describe as a “vicious cycle.”
Amara explained that early degeneration in the brainstem, which controls arousal, can lead to fragmented sleep—frequent periods of waking that interrupt rest.
Damage to the brain’s “central clock,” the suprachiasmatic nucleus, can also disrupt circadian rhythms, leading to erratic sleep patterns.
She said: “Neurodegeneration in that area can lead to abnormal sleep patterns.”
A key benefit of good sleep is the preservation of slow-wave or deep sleep, which supports the glymphatic system.
This system clears waste products from the brain that, if left unchecked, may interfere with memory and thinking.
The study raised concerns about excessive napping.
Amara noted that while napping can be helpful, overdoing it—especially late in the day—can reduce the body’s drive to sleep at night and worsen sleep quality.
She said: “There are plenty of patients I encourage to nap if they are sleepy because we want people to have adequate amounts of sleep.
“But there also certainly can be detrimental effects of napping, because if you nap a lot during the day, then you have less drive to sleep at night.
“It is important to limit naps to 20 to 30 minutes in length and to avoid napping late in the day (after about 2 p.m.),” she said.
The study did have limitations.
While actigraphy devices can measure movement, they cannot confirm whether someone is asleep, or distinguish between light and deep sleep.
The researchers used “sleep efficiency” as a proxy for quality but acknowledged its limitations.
The study also did not account for sleep apnoea, which causes repeated breathing interruptions during sleep and has been linked to cognitive decline.
Amara pointed to a 2013 JAMA Neurology study which found that those with better “sleep consolidation”—less interrupted sleep—were less likely to develop dementia, even if their genes put them at risk.
Autopsies confirmed fewer signs of Alzheimer’s in those who had slept better.
Amara stressed that dementia is not inevitable—even in later life or for those with genetic risk.
She said: “The study definitely supports that if you can improve your sleep in your 80s, you might prevent yourself from developing dementia, even that late.
“There is also some pretty good evidence that how you behave in your middle-age years, and even younger, is also important.
“It’s never too early to get started and try to reduce your risk.”
