May 31, 2023
Deep slumber may help guard against memory loss and the ravages of Alzheimer’s disease, according to two new reports. The findings add to growing evidence that sound sleep is critical for brain health.
In one study, researchers from the University of California, Berkeley, recruited 62 healthy, older adults. None had Alzheimer’s disease or other forms of dementia. Though all were free of serious memory problems, half had high levels of the protein beta-amyloid in the brain. Beta-amyloid, in its toxic form, is a hallmark of Alzheimer’s disease. As levels of the protein continue to build up in the brain, cells eventually die and memory fades.
The study participants spent the night in a sleep lab, where researchers used EEG recordings to monitor the quality of their sleep, including how much time they spent in deep sleep. During sleep, we all cycle through various phases of lighter and deeper sleep. Previous research has shown that deep sleep, also called non-REM slow-wave sleep, is critical for brain health and may help to protect the brain against the damaging effects of beta-amyloid. Deep sleep is also considered a good marker of overall sleep quality.
After sleeping, study participants completed memory tests that involved matching names to faces. The researchers found that in those who had high levels of beta-amyloid in the brain, participants who got a lot of sound, deep sleep during the night performed better on the memory tests than those who slept worse and did not get a lot of deep sleep. Deep sleep seemed to provide a compensatory boost against the effects of beta-amyloid in the brain.
Sound sleep did not provide the same boost to people who did not have high levels of beta-amyloid in the brain, the researchers found.
“With a certain level of brain pathology,” or high levels of beta-amyloid deposits in the brain, “you’re not destined for cognitive symptoms or memory issues,” said study author Zsofia Zavecz, a postdoctoral researcher at UC Berkeley’s Center for Human Sleep Science. “People should be aware that, despite having a certain level of pathology, there are certain lifestyle factors that will help moderate and decrease the effects. One of those factors is sleep and, specifically, deep sleep.”
“Think of deep sleep almost like a life raft that keeps memory afloat, rather than memory getting dragged down by the weight of Alzheimer’s disease pathology,” added Matthew Walker, the study’s senior author and a UC Berkeley professor of neuroscience and psychology. Differences in how soundly people sleep, the findings suggest, could be one reason why “two people with the same amounts of vicious, severe amyloid pathology have very different memory.” The findings were published in the journal BMC Medicine.
In the second study, published in Neurology, researchers at the Mayo Clinic in Rochester, Minn., found that older people who have a condition called sleep apnea, which interrupts deep sleep, tend to have more of the brain markers of Alzheimer’s disease.
The study looked at 140 men and women whose average age was 73. None had Alzheimer’s disease or other serious memory problems, but all had varying degrees of obstructive sleep apnea, a condition that interrupts sleep and causes people to stop breathing and wake up briefly hundreds of times during the night. Sleep apnea is often marked by snoring and feeling tired during the day
Participants spent the night in a sleep lab, where researchers recorded the amount of time they spent in deep sleep. They also underwent brain scans to look at the brain’s white matter, which forms critical connections between different parts of the brain. Tiny, abnormal areas of white matter known as white matter hyperintensities are a sign of damage. White matter hyperintensities typically increase as we age and with high blood pressure, and they are also linked to an increased risk of Alzheimer’s disease and other forms of dementia.
The researchers found that the less time people spent in deep sleep, the more white matter hyperintensities they had in their brains. Deep sleep seemed to help keep the brain “young.” People with severe sleep apnea, which interrupted sleep to a greater degree, had a higher volume of white matter hyperintensities than those with mild or moderate sleep apnea.
White matter abnormalities “are sensitive signs of early cerebrovascular disease,” said study author Dr. Diego Z. Carvalho. “Finding that severe sleep apnea and a reduction in slow-wave sleep are associated with these biomarkers is important since there is no treatment for these changes in the brain, so we need to find ways to prevent them from happening or getting worse.”
Both studies add to growing evidence that sound, restorative sleep is critical for brain health and may help gird the brain against the ravages of Alzheimer’s disease. Earlier studies have shown that the more soundly we sleep, the less buildup in the brain of beta-amyloid. Deep sleep, the kind we experience when we aren’t dreaming, appears to act as a kind of cleaning system, ridding the brain of toxic debris.
Up to a third of the U.S. population suffers from insomnia and other sleep disorders, including sleep apnea, and sleep problems generally increase as we age. If your partner complains that you snore, see a doctor for an assessment of sleep apnea. Treatments are available to promote sound sleep in people with sleep apnea.
While people often take drugs like Ambien to help them sleep, it is important to note that when sleep is drug-induced, the sleep architecture — the succession of different sleep phases, including deep non-REM sleep and their respective lengths — does not resemble the natural sleep architecture when drugs are not used. Drugs also can carry serious side effects. Furthermore, some drugs used to promote sleep may actually increase the risk of dementia.
Instead of medications, experts generally recommend cognitive behavioral therapy, which teaches people to challenge negative thoughts at bedtime with positive thoughts that induce relaxation, as the first-line treatment for sleep problems. Cognitive behavioral therapy is much safer than drugs, which should only be used short-term.
Good sleep hygiene is also important. Try to maintain a regular sleep schedule, going to bed and waking up around the same time each day. Limit the bedroom to sleeping, and not watching TV or staring at the computer screen, which can overstimulate the brain. If you can’t get to sleep after 20 minutes or so, try a relaxing bath or reading, then return to bed when you feel sleepy.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Sources: Zsofia Zavecz; Vyoma D. Shah; Olivia G. Murillo; et al: “NREM sleep as a novel protective cognitive reserve factor in the face of Alzheimer’s disease pathology.” BMC Medicine, May 3, 2023
Diego Z. Carvalho; Stuart J. McCarter; Erik K. St. Louis; et al: “Association of Polysomnographic Sleep Parameters With Neuroimaging Biomarkers of Cerebrovascular Disease in Older Adults With Sleep Apnea.” Neurology, May 10, 2023
